Pathogenesis
Enters the body through the gastrointestinal tract after ingestion of
contaminated foods, phagocytosis into the epithelial cells by interaction
of internalin (A & B) protein with E cadherin (receptor on epithelial cells)
enclosed in a phagolysosome where the low PH activates the bacteria to
produce lysteriolysine O, this enzyme lyses the membrane & allows the
listeriae to escape into the cytoplasm of the E.c, when they are proliferate
on & induce host cell actin polymerization.
Causes listeriosis (granulomatosis infant septica) may be an intrauterine
infection. The last onset syndrome causes the development of the
meningitis.
1) Actinomycetes:
Large, diverse group of G +ve, bacilli with a tendency to form chains or
filaments, facultative anaerobes that grow best in an atmosphere with
increased CO2 , young colonies produce G +ve substrate filament that
fragment into short chains. Species are identified based on cell wall
chemotype & biochemical reactions.
Pathogenesis & pathology
The bacteria bridge the mucosal or epithelial surface of the mouth,
respiratory tract, or lower gastrointestinal tract associated with dental
caries, gin gin surgical complication or trauma. Asperation this bacteria
may lead to pulmonary infection. The symptoms of thoratic
Antinomycosis resemble those of a sub acute pulmonary infection; mild
fever, cough & purulent sputum.
Diagnostic laboratory tests
Pus from draining sinuses, or specimens of tissue are examined for the
presence of sulfur granules that are hard, lobulated & composed of tissue
& bacterial filaments, which are club shaped at the periphery.
 Gram –ve rods (Enterobacteriaceae)
:This family is a large, heterogenous group of G –ve, rods whose
natural habitat is the intestinal tract of human & animals. Some
enteric organisms e.g. Escherichia coli are part of the normal
flora & incidentally cause disease, while others (salmonellae &
shigellae ) are regularly pathogenic for humans.
This family has the following characteristics : They are gram
negative rods :
 Either motile with peritrichous flagella or non motile.
 They grow well on MacConkey agar.
 Grow aerobically & facultative anaerobes.
 Ferment glucose, often with gas production.
 Catalase positive.
 Oxidase negative.
 Reduce nitrate to nitrite.
 Growth characteristics & biochemical identification:
1) Carbohydrate fermentation
2) Aminoacid decarboxylase
3) Indole production from tryptophan
4) Voges-proskuer
5) Culture of differential media such as EMB & MacConkey
agar.
6) Culture in TSI or KI
7) Culture in Christensen’s urea media for detective of urease
production.
Antigenic structure:
1) Enterobacteriaceae have a complex antigenic
structure such as :
1. O antigens represented
by LPS. Some O-specific
polysaccharides contain
unique sugars, but others
are different.
2. K antigens found in
some members of this
family. E. coli producing
K antigen cause attach of
the bacteria to epithelial
cells of GIT or UT, but
klebsiella form large
capsules consisting of
polysaccharides
(k
antigen).
3. H antigens: are located
on
flagella
the
determinants
in
H
antigens are a function of
the amino acid sequence
in
flagellar
protein
(flagellin).
2) Colicins (Bacteriocins) :
These virus-like bactericidal substances are produced by certain
strains of bacteria active against some other strains of the same
or closely related species.The Bacteriocin-producing strains are
resistant to their own bacteriocin, thus it can be used for
“typing” of organisms.
3) Toxin & Enzymes: LPS (endotoxin), exotoxin & many
enzymes.
 Escherichia :
E. coli is motile & may produce polysaccharide capsule. Most
strains ferment lactose. Producing small red colonies on
MacConkey agar. Certain strains are haemolytic when grown on
media containing suitable erythrocytes.
Antigenic structure:




LPS or somatic O antigens
Flagellar H antigens
Capsular K antigens
Fimbrial antigens : type 1 fimbriae can mediate adhesion
on a wide range of human & animal cells that contain the
sugar mannose.
Pathogenesis
Strains of E. coli possess a range of different pathogenic
mechanisms. The polysaccharides of the O & K antigens protect
the organism from the bacteriocidal effect of complement &
phagocytes in the absence of specific antibodies.
Clinical syndromes
 Urinary tract & septic infections
The infections thought to occur in ascending manner for
physiological reasons. There is evidence that the ability of E.
coli to infect the urinary tract is associated with fimbriae that
specifically mediate adherence to the Uro-epithelial cells.

Diarrhea
E. coli may cause gastro-intestinal disease ranging in severity
from mild, self-limiting diarrhea to haemorrhagic colitis.
Such strains fall into at least 5 groups:
1) Enteropathogenic E. coli (EPEC):
2) Enterotoxigenic E. coli (ETEC):
3) Enteroinvasive E. coli (EIEC):
4) Verocytotoxin- producing E. coli (VTEC):
5) Enteroaggregative E. coli (EAggEC):
 Klebsiella :
Klebsiella have capsular material which is produced in greater
amounts on media rich in carbohydrate. The capsule are all
complex acid polysaccharides, contain glucuronic acid &
pyruvic acid. They resemble the K antigens of E. coli. There is
no haemolysis of horse or sheep red cells and no motile.
Antigenic structure:
 Capsular K antigens
 Capsular O antigens
 Bacteriocins: distinct from colicins because they have no
action onE. coli.
Pathogenesis
K. pneumonia is a fairly common cause of UTI & occasionally
give rise to cases of sever bronchopneumonia, some times with
chronic destructive lesions & multiple abscess formation in the
lungs, in many can reach to blood and causes bacteremia.
 Enterobacter :
Have many features in common with those of the klebsiella; but
distinguished by their motility, the colonies may be slightly
mucoid, express a lysine decarboxylase enzyme but not arginine
decarboxylase. Enterobacter cloacae, Enterobacter aerogenes
are the most important clinically. The normal habitat is soil &
water & is occasionally formed in human feces & in the R.T.
Antigenic structure & virulence factors:
 Type I & type III fimbriae
 Most strains also express an aerobactein- mediated iron
uptake system.
 α- haemolysin
 Ompx (outer membrane protein)
Pathogenesis
The pathogenic mechanisms of these bacteria are poorly
understood, but Ompx (outer membrane) may be a pathogenic
factor for strains of Ent. cloacae, this protein appears to reduce
production of porins, leading to decreased sensitivity to βlactam antibiotics, & might play a role in host cell invasion.
Serratia :
The S. marcescens is the most commonly encountered in
clinical specimens. Capsules are not normally formed but
capsular material is formed on a well aerated medium, poor in
nitrogen & phosphate.
Most Serratia strains are motile & some strains of S.
marcescens produce red pigmented colonies on agar. The
pigment is formed only in the presence of oxygen & at a suitable
temperature; at lower temperatures growth is poorer & pigment
formation is abundant.
Pathogenesis
Most infections occur in hospital patients; they include wound
infection, septicemia, & Endocardiatis. Extracellular enzymes
may be responsible for host tissue damage. Toxins resembling
E. coli verocytotoxin & heat-labile toxin have been described.
Proteus :
There is considerable morphological variation, but in agar
grown culture the microscopical appearance is much like that of
the other coliform bacteria. All grow well on laboratory nutrient
media.
A notable property of Pr. vulgaris & Pr. mirabilis is the ability
to swarm on solid media; the bacterial growth spreads
progressively from the edge of the colony & eventually covers
the whole surface of the medium, & this growth takes place in
discontinuous manner, with each period of outward with
progress followed by a stationary period.
Tests
Indole
Citrate
H2S
Urease
Lipase
Gelalinase
Aesculin. H.
Swarming
Fermentation
Manose
Maltose
Xylose
Salicin
p. mirabilis
v
+
+
+
+
+
P. vulgaris
+
+
+
v
+
+
+
P. morgani
+
+
-
+
-
+
+
+
+
-
Pathogenesis
These bacteria create alkaline conditions in the urine because
of the ability to produce urease enzyme. These bacteria may
provoke the formation of calculi (stones) in the urinary tract.
 Shigellae :
The natural habitat of Shigellae is limited to the intestinal tracts
of human & other primates, where they produce bacillary
dysentery. G-ve bacilli, non motile, non capsulated, Shigellae
are facultative anaerobes but grow best aerobically, convex,
circular, transparent colonies with intact edges, ferment glucose,
not ferment lactose.
The genus is subdivided on biochemical & serological grands
into four species :
 Sh. flexneri
 Sh. boydii
 Sh .sonnei
 Sh. dysenteriae
Antigenic structure:
Have (O) antigens (LPS), which have a complex antigenic
pattern.
Toxins
Endotoxin (probably contributes to the
irritation of
the bowel wall)
Shigell dysenteriae Exotoxin (heat labile
exotoxin that affects on both the gut & the
central nervous system). It is protein acting
as an enterotoxin it produces diarrhea
similar to E. coli verotoxin.
Pathogenesis
Infection limited to the gastrointestinal tract; blood stream
invasion is quite rare. The infective dose is in the order of 10 3
organisms (whereas it usually is 105 - 108 for Salmonella &
Vibrios).
Essential pathologic process include:
 Invasion of mucosal epithelial cells (M cell) by induced
phagocytosis.
 Escape from the phagocytic vacuole, multiplication & spread
within the epithelial cell cytoplasm & passage to adjacent
cells.
 Microabscesses in the wall of the large intestine & terminal
ileum lead to necrosis of the mucous membrane, superficial
ulceration, bleeding & formation of a “Pseudomembrane” on
the ulcerated area, (this consists of fibrin, leukocytes, cell
debris, a necrotic mucous membrane & bacteria).
 Granulation tissue fills the ulcers & scar tissue forms.
Diagnostic laboratory tests
 Specimens: fresh stool, mucus flecks & rectal swabs for
culture. Large numbers of fecal leukocytes & some red blood
cells often are seen microscopically.
 Culture: grow on differential media (MacConkey & EMB) &
on selective media (Hektoen enteric agar or S.S agar), appear
colorless lactose negative colonies. On TsI fail to produce
H2S with acid but not gas in the bottom & an alkaline slant.
 Serology is not used to diagnose Shigella infections.
 Salmonella :
Salmonella are often pathogenic for humans or animals when
acquired by the oral route. Motile with peritrichous flagella,
they never ferment lactose or sucrose, produce H2S.
Classification of Salmonellae is based on biochemical reaction
& structures of the O, H & V antigens.
There are many serotypes:
 S. typhi
 S. paratyphi A, B
 S. choleraesuis
 S. typhimurium
 S. enteritidis
Pathogenesis & clinical findings
The organisms almost always enter via the oral route, usually
with contaminated food or drink.The host factors that contribute
to resistance to Salmonella infection are:  Gastric acidity 
Normal intestinal microbial flora  Local intestinal immunity.
Salmonellae produce three main types of disease in
humans:
A) Enteric fevers(Typhoid fever)
Produced by only a few of the Salmonellae (Salmonella typhi),
the ingested salmonellae reach the small intestine, from which
they enter the lymphatic & then the bloodstream; they are
carried by the blood to many organs including the intestine. The
organisms multiply in intestinal lymphoid tissue & are excreted
in stools.
After an incubation period of 10-14 days, fever, malaise,
headache, constipation, bradycardia & myalgia occur. The fever
rises to a high plateau & the spleen & liver become enlarged.
Rose spots, usually on the skin of the abdomen or chest are seen.
The chief complications of enteric fever were intestinal
hemorrhage & perforation.
B) Bacteremia focal lesions
This is associated commonly with Salmonella choleraesuis but
may be caused by any Salmonella serotype. Following oral
infection, there is early invasion of the blood stream with focal
lesions in lungs, bone, meninges, but intestinal manifestations
are often absent. Blood cultures are positive.
 Enterocolitis :
This is the most common manifestation of Salmonella infection
ex: S. typhimurin & S. enteritidis. After 48 hr of ingestion of
bacteria (the bacteria multiply & invade the intestinal mucosa),
there is nausea, headache, vomiting & profuse diarrhea. Blood
cultures are usually negative, but stool cultures are positive.
Diagnostic laboratory tests
1. Specimens : Blood culture in enteric fevers are often
positive in the first week of infection, urine cultures may be
positive after the second week & stool culture yield positive
from the second or third week, but for the enterocolitis the
stool culture is positive during the first week.
2. Bacteriological methods for isolation of Salmonellae :
a) Differential medium culture: EMB-Macc-Deoxycholate
medium permits rapid detection of lactose non fermenters
(S.shi-pro-ser-pseu….) & G+ve are inhibited. Bismuth
sulfite medium permits rapid detection of S. typhi, which
forms black colonies of H2S production.
b) Selective media: S.S agar, deoxycholate citrate agar
(XLD). Favor growth of Salmonellae & Shigella.
Salmonella-Shigella agar plate (SS
c) Enrichment culture: Tetrathionate broth inhibits
replication of normal intestinal bacteria & permit
multiplication of Salmonellae.
d) Biochemical identification: by using many biochemical
reactions for detection & identification of suspect colonies.
3. Serologic methods: identify unknown cultures with known
sera.
These include:
 Agglutination tests: the known sera & unknown culture
are mixed on a slide, clumping occurs within a few
minutes. There are commercial kits available to
agglutinate & serogroup salmonellae by their O antigens.
 Tube dilution agglutination tests (Widal test): the serum
agglutinins rise sharply during the second & third weeks
of salmonellae infection. Serial twofold dilutions of
unknown serum are tested against antigens from
representative Salmonella. Results are interpreted as
follows:
1) High or rising titer of O (≥1:160) suggests that active
infection is present.
2) High titer of H (≥1:160) suggests past immunization or
past infection.
3) High titer of antibody to the V antigen occurs in some
carriers.
 Other G-ve bacteria :-
 Pseudomonas aeruginosa :
Is G –ve, motile, aerobic rods some of which produce watersoluble pigments, occurs as single bacteria, in pairs &
occasionally in short chains. Widely distributed in nature & is
commonly present in moist environments in hospitals. It causes
disease in humans with abnormal host defense. Grow readily on
many types of culture media, produces smooth round colonies
with fluorescent bluish pigment Pyocyanin, which diffuses into
the agar, sometimes producing a sweet or grape-like or
corntaco-like odor.
Some strains hemolyze blood, & many strains also give a
greenish color to the agar because of the ability to produce
fluorescent pigment pyoverdin, but other strains give black
pigment pyomelanin. It grows well at 37-42 °C, oxidase
positive. It does not ferment carbohydrate but oxidize glucose.
The growth at 42 °C, with presence of characteristic pigments is
important in differentiation.
Antigenic structure
(Virulence factor)




&
enzyme,
toxin
Pili
Capsules (responsible for the mucoid colonies)
LPS
Elastases, proteases (play key role in corneal ulceration)
& two hemolysins:
Heat labile phospholipase C
Heat stable glycolipid
 Exotoxin (A) blocks protein synthesis by mechanism
similar to Diphtheria toxin.
 Phospholipases, proteases & alginate
chronic pulmonary colonization.
associated with
 Fluorecein or pyoverdin pigments act as bacterial
siderophores.
Pathogenesis
P. aeruginosa is pathogen when introduced into:
 Areas devoid of normal defense ex: mucous membrane &
skin are disrupted
 When intravenous or urinary catheters are used
 When neutropenia is present as in cancer chemotherapy.
The pathogen process
The bacteria attaches to &
colonizes the mucous membranes or skin, invade locally &
produces systemic disease, these processes are promoted by the
pili, enzymes & toxins but LPS plays direct role in causing
fever, shock, Oliguria, leukocytosis & leukopenia & adult
respiratory distress syndrome.
Diagnostic laboratory tests
 Specimens: Pus, urine, blood, spinal fluid & sputum
 Culture: Grow on blood agar & on differential media used to
grow the enteric G –ve rods. It is not lactose ferment.
 Vibrios :
V. cholerae transmission in water & is comma shaped, curved
rod, actively motile by polar flagellum, produce convex, smooth
round colonies, grow well on thiosulfate – citrate bile sucrose
(TCBS) agar, on which it produces yellow colonies, able to
grow at a very high PH (8.5 – 9.5) & are rapidly killed by acid.
Most Vibrio species are halotolerant & Nacl often stimulates
their growth.
Antigenic structure :
 Heat – labile flagellar H antigen
 O LPS that confer serologic specificity. There are at least 139
O antigen groups.
 Toxin
V. cholerae produce heat – labile enterotoxin, consisting of
subunits A&B. The somatic ganglioside GM1 in human &
mammalian cell serves as the mucosal receptor for subunit B,
which promotes entry of subunit A, into the cell. The activation
of subunit A yields increased levels of intra cellular CAMP &
results in prolonged hypersecretion of water & electrolytes.
There is increased sodium dependent chloride secretion, &
absorption of sodium & chloride is inhibited. Diarrhea occurs
with resulting dehydration, shock, acidosis & death.
Pathology
Is pathogenic only for humans. Any medication or condition that
decreases stomach acidity makes a person more susceptible to
infection with V. cholerae. Cholera is not an invasive infect, the
organism do not reach the blood stream but remain within the
intestinal tract.
The V. cholerae attach to the microvilli of the brush border of
epithelial cells. There they multiply & liberate cholera toxin &
perhaps mucinasses & endotoxin.
Diagnostic laboratory tests
 Specimens: stools
 Smears: dark – field or phase contrast microscopy may show
the rapidly motile vibrios.
 Culture: growth is rapid in peptone agar & on blood agar
with PH near 9 or on TCBs agar. A few drops of stool can be
incubated for 6 – 8 hrs in taurocholate – peptone broth (PH:
8 – 9) the organisms from this culture can be stained or
subcultured.
 Specific tests: V. cholerae organisms are furthure identified
by slide agglutination tests using anti O group. O1 & O139
antiserum & by biochemical reaction pattern.
Campylobacter :
Cause both diarrheal & systemic disease. The classification of
bacteria within the family Campylobacteriaceae has change
frequently;
There are 2 species:
 C. jejuni
 C. fetus
 C. jejuni
Are common human pathogens, causing mainly enteritis &
occasionally systemic infection. G –ve, rod with comma S, or
“gull – wing“ shapes, motile with single polar flagellum.
The colonies tend to be colorless or grey, they may be watery &
spreading or round & convex & both colony types may appear
on one agar plate such as Skirraus medium contain vancomycin,
polymyxin & trimethoprim.
Oxidase +ve, catalase +ve, non oxidase or ferment carbohydrate,
nitrate reduction & H2S production.
Antigenic structure & biologic:
 LPS
 Cytopathic extra cellular toxins
 Enterotoxin
Pathogenesis & Pathology
Acquired by the oral route (food, drink) or contact with infected
animals or animal products. 104 organisms are necessary to
produce infection. Organisms multiply In the small intestine,
invade the epithelium & produce inflammation that results in the
appearance of red & white blood cells in the stools,
occasionally, the bloodstream is invaded & clinical picture of
enteric fever develops.
 Campylobacter fetus
Is opportunistic pathogen that causes systemic infection in
Immune compromised patients. It may occasionally cause
diarrhea. The gastrointestinal tract may be the portal of entry.
Have surface array proteins which form a capsule like structure
of the organism.
 Helicobacter pylori :
Is a spiral – shaped G –ve rod, is associated with natural
gastritis, duodenal (peptic) ulcer disease, gastric ulcers & gastric
carcinoma. Have many characteristics in common with
Campylobacter. It has multiple flagella at one pole & is actively
motile. The media for primary isolation include Skirrows
medium with vancomycin, polymyxin B & trimethoprim,
chocolate medium. The colonies are translucent, oxidase +ve,
catalase –ve, strong producer of urease.
Pathogenesis
On the lumen side of the mucus, the PH is low (1 – 2), while on
the epithelial side the PH is about (7.4). H. pylori is found deep
in the mucus layer, near the epithelial surface where physiologic
PH is present, produce protease that modifies the gastric mucus
& further reduces the ability of acid to diffuse through the
mucus. Ingestion of H. pylori resulted in development of
gastritis & hypochlorhydria (which occurs when the stomach
produces insufficient amount of hydrochloric acid. This
condition is usually mistaken for acidity because the
hydrochloric acid is :  needed for the breakdown for protein
in the stomach.
 To help with the absorption of nutrients
such as calcium & iron.  To control the growth of unwanted
unicroorganisms in the digestive tract.) & found associated
between the presence of bacteria infection & duodenal
ulceration. The mechanisms by which H. pylori causes mucosal
inflamation & damage are not well defined but probably involve
both bacterial & host factors.
Bacteria
invade epithelial cell
damage mucosal cells
H. pylori surface to a limited degree
also by ammonia
Toxin & LPS
which damage
produced by the
urease activity
Chronic
&
active
inflammation (gastritis)
Diagnostic laboratory
 Specimens: gastric biopsy specimen
 Antibodies: several assays have been developed to detect
serum Ab, specific for H. pylori.
 Heamophilus influenzae :
It is found on the mucous membranes of the upper respiratory
tract in humans. It is a cause of meningitis in children &
occasionally causes of respiratory tract infection in children &
adults. G –ve, cocco bacilli, sometimes occurs in pairs or short
chains (pleomorphic forms). They have definite capsule. Small,
round, convex colonies appear on BHIA with blood, is not
hemolytic. Around staphylococcal colonies these bacteria grow
much larger (satellite phenomena). Need certain growth factors
called X & V. Factor X acts physiologically as hemin; factor V
can be replaced by nicotinamide adenine dinucleotide (NAD) or
other coenzymes. Carbohydrates are fermented poorly.
Antigenic structure:
 Capsule
 LPS
 Outer membrane proteins
Pathogenesis
The non encapsulated organ is a regular member of the normal
respiratory flora of humans. The polyribose phosphate capsule
of type B H. influenzae is the major virulence factor, therefore
is responsible for meningitis & pneumonia.
Bacteria type b
extension with
enters through
the R.T
local
involvement of
the sinuses or
the middle ear.
Less frequency, may establish
themselves in the joints to
produce septic arthritis
reach the blood
stream & may
be carried to
the membrane
 Bordetellae :
B. pertussis, a highly communicable & important pathogen for
humans, G –ve coccobacilli resembling H. influenzae with
toluidine blue stain, bipolar metachromatic granules can be
demonstrated.
Capsule is present, strict aerobe & forms acid but not gas from
glucose & lactose. It does not require X & V factors on
subculture. Hemolysis of blood-containing medium is associated
with virulent B. pertussis. Bordet-Gengou medium (potatoblood-glycerol agar).
The organism
structures:






has
many
antigenic
Pili
Pertussis toxin
Adenylyl cyclase toxin
Dermonecrotic toxin
Hemolysin
Tracheal cytotoxin
These bacteria survive for only brief periods outside the human
host. There are no vectors; transmission is largely by the
respiratory route.
Bacteria adheres & multiplies rapidly
Liberate the
Bacteria adheres & multiplies
toxins
on the epithelial surface of
onrapidly
the epithelial
surface of the trachea
the trachea & bronchi & interfere
that
with ciliary action
Liberate the toxins &
substances that irritate
& substances
surface cells, causing
coughing & marked
lymphocytosis
& bronchi & interfere with ciliary action
cells,
irritate surface
causing
coughing
& marked
lymphocytosis
Obstruction of the smaller
bronchioles by mucous plugs
Obstruction of the
smaller bronchioles
by mucous
infiltration
withplugs
There may be necrosis o
parts of the
epithelium
&
There
may be necrosis
of parts of
polymorph nuclear
(PMN)& polymorph
the epithelium
nuclear (PMN) &
infiltration with
peribronchial inflammation
peribronchial
inflammation &
intensive
pneumonia
Contributes to the frequency
of convulsions in infant
Contributes to the frequency
withofwhooping
cough
convulsions in infant with
intensive pneumonia
whooping cough
Diagnostic laboratory tests
 Specimens: Saline nasal wash, Nasopharyngeal swabs or
cough droplets expelled onto a Cough plate held in front of
the patient’s mouth.
 Direct fluorescent Ab test: can be used to examine
nasopharyngeal swab specimens, however false positive &
negative results may occur, is most useful in identifying B.
pertusis after culture on solid media.
 Culture: The saline nasal wash fluid is cultured on solid
medium agar, the M.O are identified by IFS or by slide
agglutination with specific antiserum.
 Brucella :
Obligate parasites of animals & humans, are located
intracellularly.
1) B. melitensis
infects goats
2) B. suis
3) B. abortus
4) B. conis
infects swine
infects cattle
infects dogs
The bacteria varies from cocci to rods in length, G –ve, aerobic
& non - motile, form small, convex, smooth colonies. Their
nutritional requirements are complex & cultivated on defined
media containing amino acids, vitamins, salts & glucose. It
utilizes carbohydrates but produce neither acid nor gas, catalase
positive, oxidase positive, H2S produced by many strains &
Nitrates are reduced to nitrites.
Antigenic structure:
 2 Lipopolysaccharide antigen, A & M
 Superficial L antigen (resembles
the V antigen of
Salmonella)
Pathogenesis
The common routes of infection in human are the intestinal
tract, mucosal membrane (droplets) & skin (contact with
infected tissues of animal). The organism progress from the
portal of entry, via lymphatic channels & regional lymph nodes,
to the thoratic duct & the blood stream, which distributes them
to the parenchymatous organs. Granulomatous nodules that may
develop into abscesses form in lymphatic tissue, liver, spleen,
bone marrow, & other parts of the reticuloendothelial system.
Osteomyelidis, meningitis & cholecystitis also occasionally
occurs.
The incubation period is 1-6 weeks. The onset is insidious, with
malaise, fever, weakness, aches & sweats.
Diagnostic laboratory tests
 Specimens: Blood, biopsy material & serum for serological
tests.
 Culture: Specimens are incubated in trypticase-soy broth &
on thionine-tryptose agar. Sub cultured for at least 3 weeks
before being reported as negative.
 Serology: The IgM levels rise during the first week of acute
illness, peak at 3 months & may persist during chronic
disease.
 Agglutination test: must be performed with standarized heat
killed, phenolized, smooth brucella antigens. IgG
agglutination liters above 1:80 indicate active infection. If the
serum agglutination test is negative in patients with strong
clinical evidence of brucella infections; tests must be made
for the presence of blocking antibodies.
 Blocking antibodies: These are IgA antibodies that interfere
with agglutination by IgG & IgM can cause a serologic test
to be negative in low serum dilutions (prozone) although
positive in higher dilutions.
 Yersinia :
The genus Yersinia includes Yersinia pestis, the cause of
plague. Yersinia pseudotuberculosis & Y. enterocolitica are
important causes of human diarrheal diseases.
 Y. pestis is G –ve rod that exhibits striking bipolar staining
with special stains, non-motile. Growth is more rapid in
media containing blood or tissue fluids; in blood agar
colonies maybe very small at 24 hr & when derived from
infected tissue produce gray & viscous colonies but after
passage to the laboratory the colonies become irregular &
rough. The organism has little biochemical activity.
Antigenic structure:
 LPS
 Exotoxin
 Envelope contains a protein (fraction I) acts as
antiphagocytic properties.
 A 72-kb plasmid is essential for virulence
 Coagulase
 Bacteriocin (pesticin)
 Isocitrate lyase
Pathogenesis
 Flea feeds on a rodent infected with Y. pestis
 Ingested M.O multiplies in the gut of the flea & helped by the
coagulase, block its proventriculus so that no food can pass
through.
 Blocked & hungry flea bites ferociously & the aspirated
blood, contaminated with Y. pestis from the flea, is
regurgitated into the bite wound.
 The M.O may be phagocytosed by PMN cells & monocytes.
 The Y. pestis are killed by the PMN but multiply in the
monocytes, because the bacteria are multiplying at 37°C they
produce anti phagocytic proteins & subsequently able to
resist phagocytosis.
 The pathogen rapidly reaches the lymphatics & intense
hemorrhagic inflammation develops in the enlarged lymph
nodes that undergo necrosis & become fluctuant; while the
invasion may stop there, Y. pestis often reach the blood
stream & become widely disseminated.
 Hemorrhagic & necrotic lesions may develop in all organs,
meningitis, pneumonia & serosanguineous, pleuropericarditis
are prominent features.
 The disease was known as a black death, because one of its
characteristics is blackish areas on the skin covered by
subcutaneous hemorrhages.
 Incubation period of 2–7 days, after it high fever& pain full
lymphadenopathy, commonly with greatly enlarged, tender
nodes (buboes) in the groin or axillae. Vomiting & diarrhea
may develop with early sepsis, hypotension, renal & cardiac
failure. Terminally, signs of pneumonia & meningitis can
appear.
Diagnostic laboratory tests
a- Specimens: blood, sputum, CSF.
b- Staining with Giemsa’s stain & with specific
immunofluoresent stains.
c- Culture: on blood agar & MacConkeys agar.
d- Serology: a convalescent serum, Ab titer of 1:16 or greater is
presumptive evidence of Y. pestis infection. A titer rise in two
sequential speciment continues the serologic diagnosis.
 Pasteurella :
Non motile, G –ve, cocco bacilli with a bipolar appearance on
stained smears. Aerobes grow readily on ordinary bacteriologic
media at 37°C, oxidase +ve, catalase +ve but diverge in other
biochemical reactions. Many Pasteurella species are primarily
are animal pathogens. Pasteurella multocida, P. haemolytica,
P. pneumotropica.
Clinical findings:
The most common presentation is a history of animal bite
followed within hours by an acute onset of redness, swelling &
pain. Regional lymphadenopathy is variable & fever is often low
– grade. Pasteurella infections sometimes present as bacteremia
or chronic respiratory infection without an evident connection
with animals.
 Mycobacteria tuberculosis :
Tubercle bacilli are thin straight rods. It can not be classified as
either G +ve or G –ve. Once stained by basic dyes, they can not
be decolorized by alcohol, regardless of treatment with iodine.
True tubercle bacilli are characterized by acid fastness, 95%
ethyl alcohol containing 3% hydrochloric acid, quickly
decolorize all bacteria except the mycobacteria. Acid fastness
depends on the integrity of the waxy envelope. The
mycobacteria can be demonstrated by yellow – orange
fluorescence after staining with fluorescence stains.
Culture :
Bacteria grow on selective & non selective media. The selective
medium contains Antibiotics to prevent the overgrowth of
contaminated bacteria & fungi such as Lowenstein Jensen media
which contain defined salts, glycerol & complex organic
substances.
Growth characteristics :
Obligate aerobes & increased CO2 tension, enhances growth.
Biochemical activities are not characteristic & the growth rate is
much slower than that of most bacteria. The doubling time of
these bacteria is about 18 hours, are resistant to drying &
survives for long periods in dried sputum.
These bacteria have variation in colony appearance,
pigmentation, virulence, optimal growth temperature & many
other cellular or growth characteristics.
These bacteria contain many constituents in cell walls that can
induce delayed hypersensitivity such as:
 Lipids (mycolic acids, waxes & phosphatides)
 Proteins bound to a wax fraction, can induce tuberculin &
formation of a variety of Ab.
 Polysaccharides important in inducing the immediate type of
hypersensitivity & act as antigens.
Clinical findings:
The tubercle can involve every organ system, its clinical
manifestations are protean, fatigue, weakness, weight loss &
fever may be signs of tuberculous disease. Pulmonary
involvement giving rise to chronic cough & spitting of blood
usually is associated with far advanced lesions.
Meningitis or urinary tract involvement can occur in the absence
of other signs of tuberculosis.
Pathology:
A) Two principle lesions:
Productive type
1. Exudative type
2.
1. Exudative type: this consists of an acute inflammatory
reaction with odema fluid, polymorphnuclear leukocytes
and later, monocytes around the tubercle bacilli, this type is
seen particularly in lung tissue.
2. Productive type: when fully developed, this lesion,
achronic granuloma, consists of three zones : Central area of large multinucleated giant cell
containing tubercle bacilli.
 Amid zone of pale epithelioid cell.
 A peripheral zone of fibroblasts, lymphocytes &
monocytes.
B) spread of the organism in the host
C) intracellular site of growth
Tubercle bacilli spread in the host by direct extension, though
the lymphatic channels & blood stream & via bronchial &
gastrointestinal tract.
Once mycobacteria establish themselves in tissues, they reside
principally intracellularly in monocytes, reticuloendothelium
cells & giant cells.
Lab diagnosis:
 Specimens: fresh sputum, gastric washings, urine, pleural
fluid, cerebrospinal fluid…etc.
The specimens are processed
concentrated) before use.
(decontaminated
&
 Smear: Ziehl – neelson staining (sputum & exudates).
 Culture: selective media is Lowenstein – Jenson medium.

Tuberclin test:
Material: old tuberculin is concentrated filtrate of growth in
which tubercle bacilli have grown for 6 weeks.
PPD: Purified Protein Derivative is obtained by chemical
fractionation of old tuberculin.

Reaction to tuberculin:
Skin test
(Skin injection)
“No reaction”
An individual who has not had
contact with mycobacteria
develops indurations, edema,
erythema in 24 – 48 hrs & with
very intense reaction even central
necrosis. An individual who has
had a primary infection with TB.
Mycobacterium leprae (causative agent of leprosy) :
 typical acid fast bacilli are found in scrapings from skin or
mucous membranes in lepromatous leprosy. The organisms
are often found with in the endothelial cells of blood vessels
or mononuclear cells.
 Not grown in artificial media.
 The skin lesions may occur as pale, anesthetic macular
lesionss1
–
10
cm.
diffuse
Infiltrate nodule (the erythematous) 1 – 5 cm. or diffuse
(skin infiltration)
 Neurologic disturbance are manifested by nerve infiltration &
thickening with anesthesia, neuritis, trophic ulcers & born
resorption & shortening of digits.

Two major type of leprosy:
1. lepromatous l.
2. tuberculoid l.

Lab diagnosis:
 Specimens: scrapings from skin & nasal mucosa.
 Smeared on slide & stained by acid fast stain.
There is no serological test of important.
 Treponema pallidium :
Slender spiral, actively motile, rotating steadily around their
endoflagella, even after attaching to cells by their tapered ends.
Culture on artificial media, infertile eggs; it survives best in
oxygen. Remain motile for 3 – 6 days at 25°C. Drying kills the
spirochete rapidly as does elevation of the temperature to 42°C.
Antigenic structure:
T. pallidium can not be cultured in vitro, therefore limits the
characterization of its antigens.
 The outer membrane surrounds the periplasmic space &
the peptidoglycan – cytoplasmic membrane complex.
 Not contain lipopolysaccharide.
 Endo flagella.
 More than 100 protein antigens have been noted.
Pathogenesis, pathology:
A) Acquired syphilis: the infection with T. pallidium is limited
to the human host & transmitted by sexual contact & the
infectious lesion is on the skin or mucous membranes of
genitalia. T. pallidium can penetrate intact mucous
membranes or it may enter through a break in the epidermis.
 Multiply locally of the sit of entry.
 Spread to nearby lymph nodes & then reach the blood
stream.
 In 2 – 10 weeks after infection, a papule develops of the
site of infection & breaks down to form an ulcer.
 The inflammation is characterized by predominance of
lymphocytes & plasma cells. (Primary lesion) heals
spontaneously.
 After 2 – 10 weeks of primary lesion, the secondary
lesions appear, these consist of a red maculopapular rash
anywhere on the body.
B) Congential syphilis: a pregnant syphilitic woman can
transmit T. pallidium to the fetus through the placenta
beginning in the 10th to 15th weeks of gestation.
Diagnostic laboratory tests:
 Specimen: tissue fluid expressed from early surface lesions.
 Dark field examination: a drop of tissue fluid or exudates is
placed on a slide & a cover slip pressed over it to make a thin
layer. Show typical motile spirochetes under oil immersion.
 Immunofluorescence test: fluid spread on glass slide, air
dried & fixed, stained with fluorescein labeled
antitreponemal serum & examined by means of
immunofluorescence microscope.
 Mycoplasmas :
The mycolplasmas evolved from G +ve ancestors by reducing
of genome size & are the smallest organisms that can be free
living in nature & self replicating on laboratory media.
They have the following characteristics:
1) The smallest size
2) Highly pleomorphic becomes, they lack a rigid cell wall
& instead are bounded by a triple – layered “unit
membrane” that contains a sterol.
3) They resist to penicillin because
4) They can reproduce in cell free media, on media
5) Have an affinity for mammalian cell membrane.
Typical organisms:
The morphology appears different according to the method of
examination; can not be studied by the usual bacteriologic
methods because of the small size of their colonies. Grow in
heart infusion peptone broth with 20% agar PH (7.8) & 30%
animal serum.
These bacteria pass through filters with 450 nm pore size, non
motile, many antigenically distinct species of mycoplasma have
been isolated from animal & human; three species which are
pathogen to human are:
Ureplasma urealytium, M. hominis & M. pneumonia.
Laboratory diagnostic tests:
 Specimens: throat swabs, sputum, exudates & genital
secretion.
 Microscopic examination: direct examination is useless.
 Culture: specimen inoculated onto special solid media &
incubation for 3-10 days at 37°C with 5% CO2.
 Serology: used CF tests & indirect immuno fluorescence.
Pathogenecity include
 Genitourinary disease : U. urealytium, M. hominis are
common parasites of the genital tract & their transmission is
related to sexual activity, both of them can cause
inflammation of the reproductive organs of male & female,
because it is difficult to cultivate. The Mycoplasma treatment
depends on recognition of clinical syndromes.
 Primary atypical pneumonia: has a bacterial origin. If
bacterium can not be isolate the pneumonia is called atypical
& a virus is usually suspected, if the virus can not be
detected, then mycoplasmal pneumonia, can be considered
this pneumonia caused by Mycoplasma pneumonia & they
spread through close contact & some time air born droplet;
the disease is fairly common & mild in infants & small
children & young adults.
The M. pneumonia usually infects the upper respiratory tract
& move to
the lower respiratory tract, where it attaches to
respiratory mucosal cells.
It then produces peroxide,
which may be a toxin factor, but the exact mechanism of
pathogenesis is unknown. This disease is ringed in severity
from asymptomatic to a serous pneumonia. Initial symptoms
include headache, weakness, a low fever, & a predominant
cough.
The subsequent events in infection are less well understood
but may include several factors as follows: direct cytotoxicity
through generation of hydrogen peroxide & superoxide
radicals; cytolysis mediated by antigen antibody reactions or
by chemotaxis & action of mononuclear cells & competition
for & depletion of nutrients.
 Rickettsiae :
Rickettsiae are pleomorphic coccobacilli, appearing either short
rods or as cocci, they do not stain well with gram’s stain but are
visible readily under the light microscope when they are stained
with Giemsa. Grow readily in egg sacs of embryonated eggs.
Also grow in cell culture & the generation time is 8-10 hr at 34
°C in this culture.
These bacteria have G –ve cell wall structures & the Typhus &
spotted fever groups contain LPS. These bacteria grow in
different parts of the cells. In general Rickettsiae survive only
for short times outside the vector or host, quickly destroyed by
heat, drying & bactericidal chemicals. The organism may
survive pasteurization at 60°C for 30 minutes & can survive for
months in dried feces or milk.
This may be due to the formation of endospore, like structures
by Coxiella burnetii. They are obligate intracellular.
Pathology:
Rickettsiae except for C. burnetii multiply in endothelial cells
of small blood vessels & produced vasculitis, the cell become
swollen & necrotic & there is thrombosis of the vessel leading
to rupture & necrosis.
Clinical findings:
Except for Q fever, in which there is no skin lesion Rickettsial
infections are characterized by fever, headache, malaise,
prostration, skin rash & enlargement of the spleen & liver.
a- Typhus group
Epidemic typhus
Endemic typhus
b- Spotted fever group
c- Scrub typhus
d- Q fever
Laboratory findings:
Isolation of Rickettsiae is technically different & is of only
limited usefulness in diagnosis.
The most widely used serologic tests are indirect
immunofluorescence & complement fixation test. An antibody
rise should be demonstrated during the course of the illness &
diagnosis by symptoms & by Weil – felix reaction.
Epidemic typhus:
Is caused by R. prowazekii which is transmitted from person to
person by the body louse; when a louse on an infected person.
The Rickettsia infects the insect’s gut & multiplies & large
numbers of organisms appear in the feces in about a week.
When a louse takes a blood meal, it defecates the irritation
causes the effected person to scratch the site & contaminate the
bite wound with Rickettsia. The Rickettsia then spread via the
blood stream & infect the endothelial cells of the blood vessels
causing vasculitis (inflation of the blood vessel).
 Chlamydiae :
Chlamydiae have distinctive staining properties (similar to those
of Rickettsiae); the gram reaction of Chlamydiae is negative or
variable & is not useful in identification of the agents.
They are G –ve obligate intracellular parasites & very small in
their size. Two species that cause human diseases are:
Chlamydia trachomatis & Ch. psittaci.
Some of the diseases are the following:
1. Inclusion conjunctivitis
It is an acute infectious disease caused by Ch. trachomatis
serotype D – K & it occurs throughout the world. It is
characterized by a copious mucous discharge from the eye, an
inflamed & swollen conjunctiva & the presence of large
inclusion bodies. The infection newborn acquired the
Chlamydiae during passage through an infected birth canal &
the diseases appear 7–12 days after birth. The disease in adults
acquired by contact with infective genital tract discharges, so the
genital Chlamydial infections & inclusions conjunctiva are
sexually transmitted diseases that are spread by indiscriminate
contact with multiple sex partners.
Growth & metabolism
Chlamydiae require an intracellular habitat, because they are
unable to synthesize ATP & depend on host cell for energy
requirements. Chlamydiae grow in cultures of a variety of
eukaryotic cell lines.
Classification
Are arranged according to their pathogenic potential:
A) C. trachomatis
B) C. pneumonia
C) C. psttaci