Streptococcus pneumoniae Staphylococci Gram positive cocci Lecture 46

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Streptococcus pneumoniae Staphylococci(Gram
positive cocci)Lecture 46
Faculty Dr. Alvin Fox
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KEYWORDS

• Staphylococcus aureus
• opportunistic diseases
• food poisoning/enterotoxins
• toxic shock syndrome
• toxic shock toxin
• exfoliative toxin/scalded skin syndrome
• a, ß, ? and d cytotoxins
• leucocidin
• lipase
• hyaluronidase
• protein A
• coagulase ()
• MRSA methicillin resistant S. aureus
• Staphylococcus epidermidis
• coagulase ()

• S. pneumoniae
• diplococci
• Pneumococcus
• autolysin
• bile solubility test
• optochin susceptibility
• capsule
• Quellung reaction

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S. pneumoniae
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S. pneumoniae

• leading cause of pneumonia
• particularly young and old
• after damage to upper respiratory tract
• e.g. following viral infection
• bacteremia
• meningitis
• middle ear infections (otitis media)

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S. pneumoniae

• a 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

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Autolysis identification after growth
lipoteichoic acid
autolysin
Bile
teichoic acid -choline
peptidoglycan
autolysin
Cell membrane
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C polysaccharide

• Teichoic acid
• Precipitates in serum
• C-reactive protein

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Identification
optochin resistant
optochin sensitive
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Capsule

• prominent
• virulent strains
• anti-phagocytic
• carbohydrate antigens
• vary among strains

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Capsule

• immunity
• serotype specific
• vaccine contains multiple serotypes
• - recommended susceptible population
• young children
• elderly

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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

• 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
(nares) hospital and community

• pneumonia

• osteomyelitis

• septic arthritis

• bacteremia

• endocarditis

• abscesses/boils

• other skin infections

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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

• Vomiting
• nausea
• diarrhea
• abdominal pain

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Associated with outbreak of toxic shock
syndrome.
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Toxic shock syndrome

• 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

• a toxin
• ß toxin (sphingomyelinase C)
• ? toxin
• d toxins
• detergent-like
• leucocidins

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Protein A inhibits phagocytosis
PHAGOCYTE
Fc receptor
Protein A
immunoglobulin
BACTERIUM
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Spread

• tissue-degrading enzymes
• lipase
• hyaluronidase

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Identification

• Sheep blood agar
• ß hemolytic
• yellow pigmented (aureus)

• mannitol fermentation
• coagulase-positive

• phage-typing, rarely performed

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Antibiotic therapy

• Resistance to penicillin
• penicillinase
• ß lactam antibiotics (including methicillin for
  MRSA)
• often ineffective
• modified penicillin binding proteins
• Vancomycin
• current drug of choice
• resistance has been observed

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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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Staphylococcus saprophyticus

• urinary tract infections

• coagulase-negative
• 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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Streptococcus
(pairs chains)
Staphylococcus
(Clusters)
Coagulase
Hemolysis/Test
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BETA
Bacitracin
S.
pyogenes

(group A)
S. aureus
S.
epidermidis

CAMP/
Hippurate
S.
agalactiae

(group B)
Beta hemolytic
Non-hemolytic

mannitol
mannitol
ALPHA
Optochin
/Bile Solubility

S.

pneumoniae

yellow

white


GAMMA OR ALPHA Bile
Esculin
6.5
NaCl
Group D


Enterococcus
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Bile
Esculin
6.5
NaCl
Group D


Non-
Enterococcus