Streptococcus pneumoniae
Staphylococci
(Gram positive cocci)
Lecture 38
Faculty: Dr. Alvin Fox
1
KEYWORDS
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• Staphylococcus aureus
S. pneumoniae
- coagulase (+)
diplococci
- MRSA (methicillin resistant S. aureus)
Pneumococcus
- opportunistic diseases
autolysin
- food poisoning/enterotoxins
bile solubility test
- toxic shock syndrome/toxic shock toxin
optochin susceptibility - exfoliative toxin/scalded skin syndrome
- α, β, γ and δ cytotoxins
capsule
- leucocidin
Quellung reaction
- lipase
Polyvalent vaccine
- hyaluronidase
- protein A
- coagulase (–)
- Staphylococcus epidermidis
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- Staphylococcus saprophyticus
S. pneumoniae
3
S. pneumoniae
• leading cause of pneumonia
– particularly young and old
– member normal flora, nasopharynx
– replication and spread after damage to upper
respiratory tract (e.g. after the flu)
• bacteremia
• meningitis
• middle ear infections (otitis media) - children
4
S. pneumoniae
• α hemolytic
• pneumolysin
– degrades red blood cells under aerobic conditions
• grows well on sheep blood agar
• no group antigen
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Diagnosis - spinal fluid
• direct Gram staining
• detection of capsular antigen
6
Autolysis – identification after
growth
autolysin
lipoteichoic acid
Bile
teichoic acid
-choline
peptidoglycan
autolysin
Cell membrane
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C polysaccharide
• Teichoic acid (C polysaccharide)
– precipitates in serum
– binds C-reactive protein
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Identification
optochin resistant
optochin sensitive
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Capsule
• prominent
– virulent strains
• anti-phagocytic
• carbohydrate antigens
– highly variable among strains
– numerous serotypes
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Capsular vaccine
• Immunity
– serotype specific
– to eradicate the organism in normal flora
• Vaccine
– a few major serotypes (polyvalent)
• Vaccination or the susceptible population
– young children
– elderly
• Immunization
– major serotypes susceptible to change
– population monitoring essential
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Quellung reaction
• using antisera
• capsule "fixed"
• visible microscopically
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Pathogenesis
• Teichoic acid
– complement activation
– large numbers of inflammatory cells at
infection site
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Therapy
• S. pneumoniae
–
most strains susceptible to penicillin
– resistance is common
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STAPHYLOCOCCI
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Gram positive
Facultative anaerobes
Grape like-clusters
Catalase positive
Major components
of normal flora
- skin
- nares
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Staphylococcus aureus
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One of commonest opportunistic
infections, both hospital and community
acquired:
• pneumonia
• osteomyelitis
• septic arthritis
• bacteremia
• endocarditis
• abscesses/boils
• other skin infections
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Antibiotic therapy
• Resistance to penicillin
– penicillinase
• Resistance to methicillin
‾ modified penicillin binding protein
‾ methicillin resistant S. aureus (MRSA)
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Vancomycin
• current drug of choice
• resistance observed but uncommon at this time
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Hospital infection control
• MRSA now such a problem
– monitoring by PCR of nasal swabs
– eradication
• antibiotics
• whole body antisepsis
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Food poisoning
• not an infection
• food contaminated by humans
– growth of bacteria
– production of enterotoxin
• onset and recovery both occur
within few hours
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Food poisoning
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Vomiting
nausea
diarrhea
abdominal pain
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Toxic shock syndrome.
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Toxic shock syndrome
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fever
rash
desquamation
vomiting
diarrhea
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Toxic shock syndrome
• Toxic shock toxin
- Dissemination
• Organism
– no dissemination
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S. aureus
• babies
– scalded skin syndrome
• exfoliatin
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Lytic exotoxins:
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α toxin
β toxin (sphingomyelinase C)
γ toxin
δ toxins
– detergent-like
• leucocidins
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Protein A inhibits phagocytosis
Fc receptor
immunoglobulin
PHAGOCYTE
Protein A
BACTERIUM
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Spread
• tissue-degrading enzymes
– lipase
– hyaluronidase
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Identification
• Sheep blood agar
– β hemolytic
– yellow pigmented (aureus)
• mannitol fermentation
• coagulase-positive
• phage-typing, rarely performed
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Staphylococcus epidermidis
• major member, skin flora
• opportunistic infection
- less common than S.aureus
• nosomial infections
- shunts, catheters
• artificial heart valves/joints
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Identification
• Sheep blood agar
– non-hemolytic
– Non-pigmented
• Does not ferment mannitol
• Coagulase negative
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Several other coagulase
negative staphylococcal species
• common on human skin
• some species cause opportunistic infection
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Staphylococcus saprophyticus
• urinary tract infections
• this coagulase-negative species (and others)
– not usually differentiated from S. epidermidis
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Summary Figure (Identification Scheme)
Note: S. viridans is
ALPHA hemolytic and
negative for all the tests
below
GRAM POSITIVE COCCI
Catalase
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+
Staphylococcus(Clusters)
Coagulase
+
S. aureus
Beta hemolytic
mannitol
yellow
-
S. epidermidis
Non-hemolytic
mannitol
white
Streptococcus (pairs & chains)
Hemolysis/Test
BETA: Bacitracin
S. pyogenes(group A)
+
CAMP/ Hippurate
+
S. agalactiae (group B)
ALPHA: Optochin /Bile Solubility
+
S. pneumoniae
GAMMA OR ALPHA: Bile Esculin
+
6.5% NaCl
Enterococcus
+
Bile Esculin
+
6.5% NaCl
Group D
Non-Enterococcus
Group D
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