医学微生物学
Medical Microbiology
病原生物学教研室
Department of pathogenic Biology of
Gannan Medical University
张文平
Chapter 10
Pyogenic bacterium
Pyogenic cocci化脓性球菌
Gram-positive cocci
Staphylococcus aureus
金黄色葡萄球菌
Streptococcus pyogenes 化脓性链球菌
Streptococcus pneumoniae 肺炎链球菌
Gram-negative cocci
Neisseria meningitides
Neisseria gonorrhoeae
脑膜炎奈瑟菌
淋病奈瑟菌
Pyogenic bacillus化脓性杆菌
Gram-negative bacillus
Pseudomonas aeruginosa铜绿假单胞菌
Escherichia coli大肠埃希菌属
Proteus 变形杆菌
Staphylococcus
葡萄球菌
Biological character
I. morphology
II. culture
III.Biochemical tests
IV. typing
morphology
G+, mainly
arranged in
grape-like
clusters
Gram staining
Culture
Individual colonies are circular, 2-3mm in
diameter with a smooth, shiny surface;appear
opaque and are often pigmented
Staph. aureus
Blood
agar
plate
Golden-yellow pathogenic
Staph. epidermidis
Staph. saprophyticus
white
fawn
opportunists
opportunists
Colonies of Staph. Aureus and Staph. epidermidis
Important properties
All staphylococci produce catalase（触酶）
H2O2 →O2 + H2O
S aureus
coagulase
Mannitol fermentation
staphylococcus A protein ，SPA
Binds to the Fc portion of IgG at the
complement-binding site
Significance
 Preventing the activation of complement
 anti-phagocytic
 coagglutination
resistance
Resistant to dry, heat , salt
Pathogenesis
Virulence
factors
LTA
Invasive enzyme : coagulase
toxin：lysin（αβγ ）
leucocidin
epidermolytic toxins
enterotoxins
TSST-1
Enterotoxin 肠毒素
Cause vomiting and watery, nonbloody
diarrhea
Superantigen
Heat-resistant 100℃ 30min
Toxic shock syndrome toxin 1
毒素休克综合征毒素-1
Cause toxic shock
• Tampon–using menstruating women
• Individuals wit h wound infection
• Patients with nasal packing used to stop
bleeding from the nose
superantigen
Exfoliatin
表皮剥脱毒素
(epidermolytic toxins)
Cause scalded-skin syndrome in young
children
Acts as protease(蛋白酶) that cleaves
desmosome(桥粒)，leading to the
separation of the epidermis at the
granular cell layer
coagulases
Free coagulase
Converts fibrinogen in citrated plasma into
fibrin
Bound coagulase
reacts with fibrinogen
to inhibit the phagocytosis of macrophages and
damage of bactericide substances in humor
by coating the organisms with fibrin
infections
1) purulent infection
(1). local infection skin infection:
hair folliculitis;
boil（疖）;
carbuncle(痈);
impetigo（脓疱病）.
(think pus; limited local area)
(2).organ infection: pneumonia;
meningitis（脑膜炎）
Infections
(3).Systemic infection:
Septicemia; pyemia
2) Toxin diseases
(1). Food poisoning (enterotoxin)
(2). TSS(Toxic shock syndrome)
(3). SSSS(staphylococcal scalded skin syndrome):
3) Staphylococcal enteritis
(ii) Food poisoning.
• The food becomes contaminated with the
organism from human contact, grows and
produces enterotoxin.
• The organism does not "infect" on ingestion
of food.
• Onset and recovery both occur within a few
hours.
• Vomiting, nausea, diarrhea and abdominal pain
are present.
(v) Toxic shock syndrome particularly after tampon
use includes:
• fever
• rash（皮疹）
• desquamation（脱屑）
• vomiting
• diarrhea
 Toxic shock toxin is involved.
 The organism does not disseminate.
 However, the toxin does and is responsible
for the clinical features.
Laboratory diagnosis
specimen:
*pus
* sputum (low respiratory tract infection)
* blood (septic shock, osteomyelitis,
endocarditis)
* food/faeces or vomit (food poisoning)
* mid-stream urine (pyelonephritis 肾盂肾炎 or
cystitis膀胱炎)
Laboratory diagnosis
*direct smear :gram stain
*isolation and identification: blood agar
*coagulase test
*Enterotoxin test and animal test
*Mannitol fermentation
streptococcus
链球菌
streptococcus
Biological character
G+，arranged in chains of varying length
culture
Blood agar plate
α-hemolytic streptococci
β-hemolytic streptococci
γ- streptococci
polysaccharide
groups
M
antigen
Surface protein antigen
R
S
T
Classsification:
(1).Hemolytic activity:
-hemolytic streptococcus
Incomplete hemolysis, green zone around colonies
*Opportunistic pathogens
-hemolytic/pyogenic streptococcus
Complete hemolysis, clear zone around colonies
*major human pathogens
-streptococcus
No hemolyzation, no pathogenicity.
Classification of -hemolytic streptococcus
Antigenic structure:
 Polysaccharide antigen (group-specific
antigen). 19 groups
Group A streptococci are main human
pathogens
 protein antigen (type-specific antigen).
M protein: *presents in cell wall (group A)
*Anti-phagocytosis
*adhere to epithelial cells
*clump platelet and leukocyte
*heat stable; acid stable (pH 2)
pathogenesis
Invasive
enzyme
Virulance
factors
Hyaluronidas
streptokinase
DNAases
LTA
attachment
toxin
M protein
Streptolysin (O,S)
Pyrogenic exotoxin
(scarlet fever toxin)
(1).Invasiveness
(i).surface structure
*LTA(lipoteichoic acid): adhere to sensitive cell
(epithelial cell; platelet; RBC; WBC; lymphocyte;
mucous membranes)
* M-protein : ◆anti-phagocytotic
◆Common antigen---heart muscle cell
(rheumatic fever) 风湿热
◆M-Ag Ab hypersensitivity(glomerulonephritis)
肾小球肾炎
(ii).enzyme
*Hyaluronidase (spreading factor):
Splits hyaluronic acids
bacteria spread
* Streptokinase (SK):
Lyse fibrin, prevent plasma clotting
bacteria spread
* Streptodornase (SD):
Resolve DNA
bacteria spread
(2).Toxins---exotoxin
(i) Streptolysin (hemolysin)
StreptolysinO(SLO)
oxygen-labile hemolysin
O2
(-SH-------S-S-)
antigenicity-----ASO
(antistreptolysin O)
destroy WBC, pletelet
virulence of MΦ, N.C
Streptolysin S(SLS)
oxygen stable
O2
(-SH------SH)
weak antigen
destroy WBC
virulence of
many tissues
( ⅱ ) Erythrogenic toxin (or pyrogenic
toxin /scarlet fever toxin)
 produced by most strains of group A
streptococci
 cause scarlet fever
 possess
antigenicity,
antitoxin
specifically neutralize the toxin

protien heat stable
Diseases of streptococcal infection
1 ) . Infections of group A
-hemolytic
streptococci
(1). local purulent infections:
*pharyngitis,咽炎
*erysipelas 丹毒
*puerperal fever 产褥热
(2). systemic infection : * septicemia
*scarlet fever
(3). poststerptococcal diseases (hypersensitive disease)
(i) acute glomerulonephritis ( group A)
mechanism:
*type III hypersensitivity (most)
M protein-Ab
immune complex
*type II hypersensitivity
common Ag
deposition
glomerular basement
cross reacts with
glomerular
Membrane
basement membrane
activation C3,C5
tissue destruction
tissue destruction
(ii) Rheumatic fever (many types of group
A streptococci)
mechanism:
*immune complex  (deposition)
heart, joints  type III hypersensitivity
*common
Ag

crossreactionheart
type II hypersensitivity
Clinical diagnosis
Gram stain
based on cultures from
clinical specimens
ASO
Serologic
methods
Normal titer 1:400
Acute glomerulonephritis and acute
rheumatic fever.
Prevention & treatment
*Treat the pharyngitis and tonsillitis in
time, avoid the post streptococcal
diseases.
*Antibiotics
and
chemical
agents:
penicillin G for the first choice
Streptococcus pneumoniae
Streptococcus pneumoniae
 S. pneumoniae is a leading cause of pneumonia in
all ages (particularly the young and old), often
after "damage" to the upper respiratory tract
(e.g. following viral infection).
 It also causes middle ear infections (otitis media).
 The organism often spreads causing bacteremia
and meningitis.
 S. pneumoniae is α-hemolytic and there is no
group antigen.
 Direct Gram staining or detection of capsular
antigen in sputum can be diagnostic.
 The organism grows well on sheep blood agar.
Autolysin
 Pneumococci are identified by solubility in bile.
 An autolysin (peptidoglycan degrading enzyme)
is released by bile from the cell membrane and
binds to a choline-containing teichoic acid
attached to the peptidoglycan.
 The autolysin then digests the bacterial cell wall
resulting in lysis of the cell.
The optochin test is a presumptive test that is used to identify
strains of Streptococcus pneumoniae. Optochin
disks are placed on inoculated blood agar
plates. Because S. pneumoniae is not optochin resistant, a
zone of inhibition will develop around the disk where the
bacteria have been lysed. This zone is typically 14mm from
the disk or greater.
Not optochin sensitive
optochin sensitive
Capsule
 This is highly prominent in virulent strains and its
carbohydrate antigens vary greatly in structure
among strains.
 The capsule is anti-phagocytic and immunization
is primarily against the capsule.
 Capsular vaccines are available for susceptible
individuals; immunity is serotype-specific.
Neisseria
Gram negative cocci, usually arranged
in pairs.
Some are normal inhabitants in
respiratory tract. Others are human
pathogens
(eg: gonococcus,meningococcus )
…
Common biological characteristics
1.Gram negative cocci, kidney-shaped, in
pairs have capsules and pili
2.Need enriched medium (chocolate blood
agar )
3. 5~10%CO2
4.Resistance: very weak “fragile”, extremely
sensitive to drying, heat, cold
Neisseria meningitidis
脑膜炎奈氏菌
Meningococci and their colonies
Pathogenicity and immunity
1. Pathogenicity:
(1)
Human is the only natural host for
pathogenic meningococci.
Child: susceptible (lacking specific Abs)
(2) virulence factor:
*Pili– attach to nasopharyngeal mucosa
*capsule – antiphagocytosis
*endotoxin – main pathogenic substance
capillary tube, small blood vessel
2.Pathogenesis:
epidemic cerebrospinal meningitis
流行性脑脊髓膜炎
clinical typing: common, outbreak,
septicemic type
Clinical cause: 3 stages
(1)Organisms  nasoparynx ( nasopharyngeal
infection : asymptomatic , most are carriers,
only 2~3% go to next stage )
(2) blood stream <fever, skin ecchymosis >
cross
the
brain
barrier
<severe
headache
,vomitting,
stiff
neck
>
(meningococcemia. bacteremia or septicemia.
blood contain cocci )
(3)meninges (meningitis. meninges pyogenic
inflammation. spinal fluid contain cocci )
Immunity:
group-specific antibody, cross-immunity
between groups.
III. Laboratory diagnosis
1. specimen: spinal fluid, blood, nasopharyngeal
swabs .
(*note: “fragile” bed-side inoculation)
2. direct smear :
smear Gram stain (G- diplococci, within
white cells)
3. isolation and identification:
specimen serum broth  chocolate blood
agar plate (5~10% CO2 ,37C )  Gram stain
and biochemical, serological identification
4. serologic test : to detect the unknown Ag
with given Ab
Prevention and treatment
1. Polysaccharide vaccine (group A, C)
2.Penicillin;cefotaxime; chloramphenicol
Neisseria gonorrhoeae
Gonococci and their colonies
1. Pathogenic factors
* Pilli: attach to epithelial cells (urinarygentital, RBC)
* IgA 1-protease: break down surface IgA
antibodies.
*Outer membrane protein (OMP):
Diseases:
*Gonorrhea
(STD: sexually transmitted
disease)
acute urethritis尿道炎(male);
pelvic inflammatory 盆 腔 炎
(female)
*Ophthalmia
neonatorum→blindness
新生儿眼结膜炎
Laboratory diagnosis
Specimen:
purulent
secretion
of
genitourinary tract
Isolation and identification: direct smear,
culture, biochemical tests
Prevention and treatment
*penicillin----- Gonorrhea
*silver
nitrate
---neonatorum
ophthalmia