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Lecture 6
Dr. Ismail I. Daood
Medical Microbiology
GENUS : Streptococcus :
The
Streptococcus
are gram-positive spherical bacteria that
general characteristically arranged form pairs or chains of varying length,
during growth . The genus Streptococcus includes a large number of
species some of them are pathogens, and others are normal flora of the
Oropharynx and Gastrointestinal, Urinal tract , skin ,etc.
Diseases associated with Streptococci range from dental plaque and
trivial skin infections to life threatening complications such as :
Necrotizing
fasciitis,
Toxic
shock,
Rheumatic
fever,
and
Glomerulonephritis.
Streptococcus are gram positive cocci form linear chains of varying
length, non motile, non sporing. They require enriched media with blood,
serum or chocolate agar. The most pathogenic type for human :
1 - Streptococcus pyogenes.
2 - Streptococcus pneumoniae
3 - Streptococcus viridans or viridans streptococcus include ( S
mitis , S mutans , sanguis ,and others ).
4 – Streptococcus bovis .
5 – Streptococcus agalactiae
Classification :
1. Depend on oxygen (O2) requirement :
a. aerobes
b. obligate anaerobe
c. facultative anaerobes.
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2. Depend on colony morphology and the hemolytic reactions on
blood agar :
a. Alpha () hemolytic Streptococci incomplete haemolysis which
green appearance a zone of greenish around the colony e.g. Strep.
viridans .
b. Beta () hemolytic Streptococci complete haemolysis which
produces a clear colures zone of haemolysis in blood agar, e.g.,
Streptococcus pyogenes (group A & B).
c. Gamma hemolytic Streptococci . Non-hemolytic.
3. Serological specificity of the cell wall or capsular antigens such as
classify S pneumoniae into over 90 types .
4. Biological reaction and resistance to physical and chemical factors
Biochemical reaction :
Biochemical tests include sugar fermentation , tests for the presence of
enzymes .
Streptococcus are non-fermented lactose, but fermented
glucose, maltose producing acid but no gas. Manitol fermented by Strep.
pyogenes but Strep. viridans not ferment . Catalase negative, don’t
liquefy gelatin, capsule ( +ve ).
Pathogenicity :
Most streptococci that contain the group A antigen Streptococcus
pyogenes , It is prototypical human pathogen, produces large (1 cm in
diameter ) zones of beta haemolysis around colonies It is more invasion
and immunologic disorders
and produce septicemia , respiratory
infections, scarlet fever, toxic shock syndrome ,skin infection, abses,
acute rheumatic fever, endocarditis, glomerulonephritis, arthritis,
meningitides.
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Virulence factors of Streptococcus :
1. Protein M (antiphagocytic and anticomplement)
2. Protein F (for adhesion to bind to pharyngeal epithelial cells causes
disease.
3. Protein G ( bind IgG preventing phagocytosis )
4. Substance C ( became to development diseases ).
5. Exotoxins ( Exotoxin A & B and cardiohepatic toxin ) causes heart
and liver failure.
6. Hemolysins as ( Striptolysin O & S ).
7. Capsule (mucopolysuccharids ) most group A to impede
phagocytosis
Laboratory diagnosis :
a. Rapid diagnostic test. ( specimens, smears and swab ).
b. Culture and isolation by bacteriological investigation
c. haemolysis pattern and bacitracin and optochin sensitivity.
Strep. pyogenes ( +ve ) to bacitracin
Strep. pneumoniae ( +ve ) to optochin.
d. Total and Differential leucocytes count.
e. ESR test
f. Serological and Antigen detection test.( antistreptolysin ) ASO titer.
Treatment :
Penicillin G but resistant strain as culture sensitivity. Third generation
cephalosporin's, vancomycin, riphampin, new generation as azithromycin
or clarithromysin.
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Gram-Negative Cocci : Neisseriaceae :
General characteristic :
The family
Neisseriaceae includes Neisseria and other genus and
several species . Neisseria are Gram-negative cocci, that usually occur
in pairs . N gonorrhoeae (gonococci ) and N meningitidis
(meningococcoi ) are pathogenic for human , some Neisseriae are normal
inhabitants of the human respiratory tract . ranging from 0.6-1.0 m in
diameter, kidney-shaped seen as Diplococci, nonmotile, capsulated ( +
ve ), aerobic, oxidase
( + ve ), catalase ( + ve ), individual cocci are
kidney-shaped , complex growth requirement ; grow best on chocolate
agar as heated blood , hemin , under increased carbon dioxide CO2 5%
optimum temperature at 37oC. Fermented carbohydrate .
Classification :
The Neisseria genus contains two important pathogenic species :
1. Neisseria meningitidis ( Meningococcoi ) causes cerebrospinal
meningitis in human.
2. Neisseria gonorrhoeae (gonococcus) causes gonorrhoeae in
human.
3. Other Commensal species non-pathogenic for human
as N.
pharynges , N sicca , N mucosa
1. Neisseria meningitides :
Neisseria meningitides is determinants as pathogenicity because it
has virulence factors :
a. Adhesion factors : Fimbriae and pili.
b. Capsule.
c. Endotoxin ,Lipopolysaccharide (LPS).
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d. IgA proteases, which cleave IgA protect bacteria against the
effects of secretary IgA.
Pathogenesis :
N. meningitidis is causes meningitis in children, older children,
adolescents and adults by inhalation of contaminated droplets, clinical
disease and symptoms include, severe headache, fever, stiff neck,
vomiting, neurologic signs, myalgias and athralgias, mental status and
coma, hypotension, multiple organ failure and septic shock. Also causes
pharynitis, pneumonia.
2. Neisseria gonorrhoeae :
Neisseria gonorrhoeae is determinants as pathogenicity because it
has Virulence factors :
a. pili and fimbriae for adherence to host cells.
b. Outer membrane proteins (1 and 11)
c. Endotoxin less toxic than N. meningitides
d. Capsule
e. Peptidoglycan
f. Enzymes, IgA protease and Beta-lactamase.
Pathogenesis :
N. gonorrhoeae is adhere to the surface of epithelial cells by
adhesion and invasion those of urethra, genital tract, rectum and throat
clout disease and causes arthritis, cevicitis, pelvic inflammatory disease,
anorectal gonorrhea.
Lab. Diagnosis :
a- Identification local disease by swab examine the bacteria
microscopy directly.
b- Culture and isolation
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c- Serology test
d- Direct immunofluorescence ( using fluorescent ant-N.
gonorrhoeae Antibodies ).
Treatment :
Combination of drugs common STD, Ceftriaxone, Cefixim as oral
dose, Cefotaxime, Amoxicillin, Ciprofloxacin.
Moraxella :
Moraxella catarrhalis was named Branhamella catarrhalis and
before that Neisseria catarrhalis this organism causative agent is ranked
third behind H. influenzae and S. pneumonia causes otitis media,
sinusitis, pneumonia , conjunctivitis , bronchitis, tonsillitis bacteremia
and septicemia. It is cocci, diplococci gram ( -ve ), oxidase-positive,
DNase ( +ve), catalase (+ve) aerobic, colonize in oral and nose. Most
strains of M catarrhalis from clinically significant infections produce
Beta lactamase .
Gram-Positive Rods Bacteria / ( Bacilli ) :
The gram-positive rods can be classified as either non-spore forming
or spore forming. Clostridium and bacillus are both spore-forming.
Clostridium are anaerobic and bacillus are aerobic.
Anaerobic Clostridium :
The genus clostridium include over 50 species gram-positive ,spore
forming bacilli . most common pathogens :
1. Clostridium perfringens (welchii)
2. Clostridium tetani
3. Clostridium botulinum
4. Clostridium difficile.
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1. Clostridium perfringens :
Clostridium perfringens
causes ( most associated) with
gas gangrene. There are at least 12 different soluble antigens which there
are five types from A to E distinguished by the various of toxins produce.
All types produce the alpha toxin have varying activities , including tissue
necrosis and haemolysis . Also associated with food poisoning. It is gram
positive, bacillus, about 4-6 m by 1 m, capsulate when seen in tissue,
anaerobe, grows rapidly at 37oC in cooked meat broth and even more at
up to 45oC. spore resist forming, grow on blood agar colonies are large,
round, smooth regular with complete haemolysis, non motile.
Pathogenicity :
Cl. perfringens produces 12 exotoxins and enterotoxin .Gas gangrene
occurs when a soft tissue wound is contaminated by Cl. Perfringens ,as
occurs in trauma , septic abortion , and war wounds .Bacteremia
associated with Cl. Perfringens can be rapidly fatal.
a- Exotoxins (-toxin, -toxin, E toxin and T-toxin). All of toxin are
lethal.
c- Enterotoxin (inhibit glucose transport, causes protein loss, and
damages the epithelium).
b- Causes skin and soft tissue infections, wounds infection as
exogenous contamination occur (e.g., from soil, water or sewage)
and endogenous contamination cause infections most are secondary
to abdominal surgery or trauma which allow contamination of
tissues with fecal or genital tract secretions. Localized cellulites,
enteritis necrotic, gas gangrene (myonecrosis) . Food poisoning (
type A spores ).
Clostridium tetani :
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