Gram positive cocci Flashcards
(31 cards)
Gram positive bacterial cell wall
Has a thick peptidoglycan layer that contains teichoic and lipoteichoic acids
Gram negative bacterial cell wall
Has a think peptidoglycan layer and an outer membrane that contains lipopolysaccharide (LPS), phospholipids, and protein
What is the colour of positive gram staining bacteria?
Purple
What is the colour of negative gram staining bacteria?
Pink or Red
Gram positive cocci arranged in singles, pairs, tetrads or grape-like clusters.
Non-motile, non-spore forming but occasionally capsulated
Aerobic and facultative anaerobic, catalase positive, and oxidase negative
Staphylococci
What are the three staphylococcal species?
Staphylococcus aureus, epidermis, and saprophticus
What is the confirmatory test for Staphylococcus aureus?
Coagulase test. Only staphylococcus aureus is coagulase positive which differentiates it from other species.
It produces an enzyme called coagulate that converts fibrinogen to fibrin, promoting clotting of blood or plasma.
How to differentiate Staphylococcus aureus and epidermis on Mannitol Salt Agar (MSA)?
Staphylococcus aureus turns the agar yellow as it ferments mannitol with acid.
The agar remains pink for Staphylococcus epidermis
What is the observation of S.aureus colonies on BPA?
Black colonies due to the reduction of tellurite in egg yolk
The clear zones surrounding the black colonies indicates the production of lecithinase, the breaking down of egg yolk
What is the observation of S.aureus colonies on blood agar?
Beta-haemolytic, complete lysis of blood
Catalase test
2H2O2 —> 2H2O + O2
The formation of bubbles indicates a positive rsesult
How is S.aureus transmitted?
Direct contact or exposure to contaminated fomites
Structural: Protein A (helps to invade immune system by binding to IgGA), capsule, teichoic acid, peptidoglycan, and slime layer
Toxins: cytotoxin, exfoliative toxin (ritter’s syndrome), enterotoxins (food poisoning), and TSST-1 (toxic shock syndrome)
Enzymes: coagulase and hyaluronidase
S.aureus virulence factor
- enterotoxin (contaminated food)
- symptoms: vomiting, nausea, diarrhea, abdominal cramps
Staphylococcal food poisoning
- exfoliative toxin
- symptoms: peeling off skin, exfoliative dermatitis, fever (infections)
- most commonly in children
Staphylococcal scalded skin syndrome (ritter’s disease)
1) Skin: Folliculitis and impetigo
2) Blood: bacteremia, septicemia, and endocarditis (travel to heart)
3) Bone: osteomyelitis and septic arthritis
4) Brain: meningitis and brain abscess
Inflammatory diseases of S.aureus
- TSST-1
- symptoms: fever, myalgia, hypotension, vomiting, diarrhea, and rashes
Staphylococcal Toxic Syndrome
Penicillin cannot be used
Derivatives of penicillin: nafcillin, oxacillin, and methicillin
MRSA: cephalosporins
MRSE: vancomycin + rifampicin
VRSA: vancomycin intermediate
Treatment for Staphylococci
Gram positive cocci, chains, catalase negative, oxidase negative, Beta-haemolytic, Group A
Streptococcus pyogenes
Conformational test for S.pyogenes
Streptococcal grouping (Lancefield classification)
Aerobic and facultatively anaerobic, Gram positive cocci, arranged in pairs or chains. Non-motile, non-sporing, catalase negative.
Classified by:
Group specific carbohydrates
Haemolytic properties
Streptococcus
Structural: capsulated, teichoic acid, M and F protein
Toxins: Streptococcal pyrogenic exotoxins (SPEs), Streptolysin O and S, Pyrogenic exotoxins
Enzymes: ribonucleases, hyaluronidase, and streptokinase
Virulence factor of S.pyogenes
Respiratory infections
- pharyngitis (strep throat)
S.pyogenes
skin infections
- cellulitis
- pyoderma
-necrotizing fasciitis
S.pyogenes
