Lecture 7
Dr. Ismail I. Daood
Medical Microbiology
Clostridium tetani :
Clostridium tetani which causes tetanus, is worldwide in distribution
in the soil and in the feces of animals and human. It has specific flageller
antigens, all type produce same neurotoxin, tetanospasmin. Small
amounts of toxin can be lethal for humans. The vegetative cells of
C tetani produce the toxin tetanospasmin which binds to motor neurons
that effect to the spinal cord and brain .
Pathogenesis :
C tetani not invasive organism . The infection remains localized in the
area of tissue ( wound, burn, injury, surgical suture )in which the spores
have been introduced , and the disease is entirely a toxemia. Germination
of the spore and development of vegetative that produce toxin are aided
by necrotic tissue, calcium salts, and pyogenic infections ,then the toxin
released reaches the central nervous system (CNS) and rabidly become
fixed to receptors in the spinal cord and brain.
Treatment :
Intramuscular administration of 250-500 units of human
antitoxin ( tetanus immune globulin ) to neutralizes the toxin
that has not been fixed to nervous tissues . Patients who develop
symptoms of tetanus should receive muscle relaxants , sedation,
and assisted ventilation. Sometimes surgical to removes the
necrotic tissue . Penicillin inhibits the growth of C tetani and
stops toxin production .
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Prevention of tetanus depend on :
1. active immunization with Toxoids.
2. care of wounds contaminated with soil, etc.
3. prophylactic use of antitoxin
4. administration of penicillin.
Enterobacteriaceae \ Enteric Gram-Negative Rods :
Enterobacteriaceae are a large, heterogeneous group of
gram-
negative rods ( bacilli ) whose natural habitat is the intestinal tract of
human and animals . The family includes many genus ( Escherichia,
Shigella , Salmonella, Enterobacter , Klebsiella, Proteus and others ).
referred to as "enteropathogenic bacteria" or enteric bacilli or simply
enteric these involved in extra intestinal infections. Some enteric
organisms e.g. Escherichia coli , are part of the normal flora and
incidentally cause disease . Most of them are opportunistic pathogens
infected human, general characteristics of it : Gram-negative rods, nonspore-forming facultative anaerobic, grow in simple media ferment
glucose and produce acid, motile, have peritrichous flagella capsulated.
Major enteropathogenic bacteria :
Enterobacteriaceae (these bacteria may also be called coliforms).
a.
Opportunistic
bacteria
Escherichia
coli
(most
strains),
Citrobacter spp., Shigella spp. , Salmonella spp., Enterobacter spp. ,
Klebsiella spp. , Proteus spp. .
b. Pathogenic bacteria
- E. coli (some strains)
Shigella
- Shigella dysenteriae. S., flexneri, S. boydii S. sonnei
Salmonella
- Salmonella typhi , - Salmonella paratyphi A&B
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Escherichia coli :
General properties of E. coli
the normal intestinal flora member
gram –ve ,motile ,non-spore forming , a typically produces positive tests
for indole, lysine decarboxlase and manitol fermentation , hemolysis on
blood a agar ,produces gas from glucose .
and certain related bacteria
(e.g. Klebsiella, Enterobacter, Citrobacter) form the group known as the
Coliforms.
- Characteristics of E. coli :
Ferments lactose on MacConkey agar
Produce gas when fermenting glucose
Produce indol when breaking down tryptophan
Gram-negative, Motile ,
Virulence factors : Exotoxin and Endotoxin
- Pathogenesis of E. coli :
E. coli cause gastroenteritis, urinary tract infection, neonatal meningitis,
secondary pneumonia nosocomial infections The most serotype
pathogenic . E coli-Associated Diarrheal Diseases :
Enteropathogenic E coli (EPEC)
Enterotoxigenic E coli (ETEC)
Enterohemorrhagic E coli (EHEC)
Enteroinvasive E coli (EIEC) verotoxin very similar to shigellosis
Enteroaggregative E coli (EAEC) causes acute and chronic diarrhea
-Lab diagnosis
Clinical picture, age of patient, travel history are important in
diagnosis. Sample from feces, infected tissue, blood, urine collected are
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using for visitation of UTI and cultured on media and differential media.
Biochemical analysis and stereotyping.
- Treatment
Rehydration with electrolyte-rich antibiotics used in patients with
chronic infections of their location Trimethoprim-sulfamethoxazol.
Shigella :
Shigellae are nonmotile and usually do not ferment lactose but do
ferment other carbohydrates, producing acid but not gas. They do not
produce H2S. The four Shigella species are closely related to E coli.
General properties of Shigella :
Gram-negative, non-motile non-fermented lactose on MacConky agar,
not produce gas from fermented carbohydrate, not produceH2S from
thiosulfate.
a. Group A. S. dysenteriae.
b. Group B. S. flexneri.
c. Group C. S. boydii.
d. Group D. S. sonnei.
- Pathogenesis :
Shigella is the agent of bacterial dysentery shigellosis, it causes watery
diarrhea, severe abdominal cramps, stools containing blood and mucus.
- Lab. Diagnosis :
Shigella must be isolated from sample :
Feces, rectal swab, mucosal ulcer cultured on media and
selective media as SS agar MacConky agar.
- Treatment :
supportive therapy by fluid replacement. Antibiotics Ampicillin,
Amoxicillin,
Trimethoprim-sulfamethoxazol,
Cefalosporines.
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new
generation
of
Salmonella : Salmonellae are often pathogenic for humans or animals
when acquired by the oral route. They are transmitted from animals and
animal products to humans, where they cause enteritis, systemic
infection, and enteric fever. General properties of Salmonella are :
Gram-negative, motile, non-spore forming non-fermented lactose on
MacConkey agar produce gas when fermenting glucose, produce H 2S
from thiosulfate. (TSI)
Major species include :
-
Salmonella typhi
-
Salmonella paratyphi A and Salmonella paratyphi B
-
Salmonella enteritidis
Pathogenesis :
-
Endotoxin contain LPS with D antigen.
-
Invasine adherence to and penetration of intestinal epithelial cell
-
Capsule resistance to phagocytosis.
-
Iesistance to acidic pH of stomach.
-
Vi Virulence antigen (special capsule polysaccharides . causes
Enterocolitis (Salmonellosis).
Lab. Diagnosis:
Culture and isolation are essential to confirm infection based on
biochemical test.
Treatment : Chloramphenicol, Amoxicillin or Ampicillin with
Trimethoprim-sulfamethoxazol, Quinolones (Ciprofloxacin). Ceftrixon.
Vibrionaceae
Vibrio cholerae :
General properties of Vibrio cholerae is a comma
shaped, rod 2–4mm long, gram-negative, motile Oxidase-positive with
single polar flagellum non-spore curved. It is actively motile by means of
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a polar flagellum. On prolonged cultivation, vibrios may become straight
rods that resemble the gram-negative enteric bacteria
- Major species :
1. Classic cholera O1 group – two biotype. El Tor and classic. about
75% of infections with the El Tor biotype. The incubation period is
1–4 days for persons who develop symptoms, depending largely
upon the size of the inoculum ingested. There is a sudden onset of
nausea and vomiting and profuse diarrhea with abdominal cramps.
Stools, which resemble "rice water," contain mucus, epithelial
cells, and large numbers of vibrios
2. Non-O2 group. – pathogenesis :
Enterotoxin (choleragen) Aregion & B region
- Adhesion factors, adherence and colonization secretion of cholera toxin.
Increased adenylcyclase activity and accumulation of(cAMP).
Lab Diagnosis.
Fecal samples cultured on selective media, alkaline peptone broth,
V cholerae grows well on thiosulfate-citrate-bile-sucrose (TCBS) agar,
on which it produces yellow colonies that are readily visible against the
dark-green background of the agar. Vibrios are oxidase-positive.
Treatment :
-
Fluid replacement as intravenous glucose solution or oral 2%
glucose sol.
-
Antibiotics therapy drugs of choice are tetracycline
chloramphenicol, and cephalosporins.
Chlamydia
Chlamydiae that infect humans are divided into three species:
Chlamydia trachomatis,
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Chlamydia pneumoniae,
Chlamydia psittaci
The Chlamydiae can be viewed as gram-negative bacteria that lack
mechanisms for the production of metabolic energy and cannot
synthesize ATP. Thus, Chlamydiae are obligate intracellular parasites.
Pathogenesis :
The incubation period for chlamydial conjunctival infection is 3–10
days. In endemic areas, initial trachoma infection occurs in early
childhood,. Chlamydial infection is often mixed with bacterial
conjunctivitis in endemic areas, and the two together produce the clinical
picture.
The
mucopurulent
earliest
symptoms
discharge,
of
conjunctival
trachoma
are
hyperemia,.
lacrimation,
Microscopic
examination of the cornea reveals epithelial keratitis. It includes agents of
human disorders such as trachoma, inclusion conjunctivitis, nongonococcal urethritis, cervicitis, pneumonitis of infants.
Treatment :
Sulfonamide, Erythromycin, and Tetracycline have been used to suppress
Chlamydia and bacteria that cause eye infections.
Mycobacteria :
The mycobacteria are rod-shaped, aerobic bacteria that do not form
spores. Although they do not stain readily, once stained they resist
decolorization by acid or alcohol and are therefore called "acid-fast"
bacilli. The most human pathogens are:
- Mycobacterium tuberculosis causes tuberculosis (TB)
- Mycobacterium leprae causes leprosy.
- Mycobacterium avium -intracellulare (M avium complex, or MAC).
- Other atypical mycobacteria frequently infect patients with AIDS, are
opportunistic pathogens in other immunocompromised persons, and
occasionally cause disease in patients with normal immune systems.
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General properties :
- slow-growing
- Bacteria shape slender, straight or curved rods
- Survive after ingestion by macrophages.
Mycobacterium tuberculosis (TB)
Motuberculosis are slender rod, (comma), acid-fast staining, slow
growing, microaerophilic, or aerobe, grow best at 37 oC temp. contains
glycolipid as mycolic acid in the outer surface of cell wall. Antibacterial
resistance.
Pathogenesis :
Infection the lower lung primary infection, cause active tuberculosis,
phagocytosed bacilli will diffuse through the lymphatic vessels and the
blood stream reactivation of a latent infection may occur 20 years or
lougher after primary infection. Clinical signs include coughing,
hempotypsis, after noon fever, weight loss, and malaise.
Lab. Diagnosis :
Sample from sputum culture on special media required long incubation
1 to six weeks colonies appear, Tuberculin Test , volume is usually 0.1
mL injected intracutaneously, A positive tuberculin test does not prove
the presence of active disease due to tubercle bacilli. Isolation of tubercle
bacilli provides such proof .Also chest X-ray used.
Treatment :
Bacteria resistance to antibiotics, treatment should be continued for
several months depending on the severity of the disease, the drugs The
two major drugs used to treat tuberculosis are isoniazid and rifampin.
The other first-line drugs are pyrazinamide, ethambutol, and
streptomycin.
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