Gram pos. cocci Flashcards
2 primary tests that indicate isolate as staphylococcus
- Catalase : Pos
- O/F: ferment
- Oxidase test: Neg
What’s the difference b/w plasma & serum?
Serum: No fibrinogen (bc consumed when it clots)
Plasma: anticoagulated fibrinogen available
Type of infection S. saprophyticus associated with? & what is given in the Novobiocin test
- Community aquired UTI
- resist novobiocin
List 2 virulence factors of S. epidermis
- produce biofilm= resistant to antibiotic & immune resp.
- readily acquires resistance from other bact. (pass plasmids)
What does MRSA stand for?
methicillin resistant to Staphylococcus aureus
List 4 virulence factors of S. aureus & give e.g. of why or how organism able to cause infection
- Capsular polysaccharides: adherence, protect from immune resp
- Protein A: prevent detection of phagocytes
- Enzymes: B-lactamases resistance to penicilin or other B-lactam antibiotics;
- Haemolysins: toxic to host cells
- Toxins: enterotoxins (A->D, E, H, I= heat resitant)
What test separates Staphylococci into 2 groups?
Coagulase test
+ve: S. aureus
-ve: S. saprophyticus, S. epidermis
Explain theory of coagulase test (how it works)*
- SLIDE: bound coagulase (Cwall) aka “clumping factor”. Fibrinogen in plasma clumps w/ coagulase on Cwalls of cells=> white clumps
- TUBE: free coagulase (secreted). Incubate for 4 hrs in plasma & let bact. secrete coagulate => clots w/ fibrinogen
Before ID & reporting, what factors of clinical relevance need to be proven for coagulate negative staphylococci (CoNS)?
- Purity of growth
- quantity of growth
- site of infection
- clinical history
What type of infections is S. epidermis normally associated w/ & why?
Noscomial infections bc:
- Surgery & implants
- readily acquires resistance from other bact.
- produce biofilm on artificial surfaces => resist antibiotics & immune resp
What’s the scientific name for group A streptococcus?
Streptococcus pyogenese
What’s the scientific name for group B streptococcus?
Streptococcus agalactiae
What antibiotic is the drug of choice used to treat suspected streptococcal pharyngitis?
Pharyngitis from a streptococcal may be from to S. pyogenese = Group A=> Bacitracin sensitive/susceptible
What organism would this be? GPC, catalase neg & hippurate pos
Streptococcus agalactiae
What organism would this be? GPC, catalase neg & sensitive to Bacitracin
Streptococcus pyogenese
How do you differentiate S. pneumoniae & a member of Viridans streptococci?
by Optochin / Bile solubility tests.
S. pneumoniae: susceptible & soluble
Viridans streptococci: reistan & insoluble
what’s the reservoir of Strepococcus pyogenes & what area does it inhabit?
a) humnas
b) (mucous membranes) in pharynx (URT)
What can Viridans streptococci cause?
Endocardiditis (lead to septacaemia)
Which sp. of Enertococcus is common for human clinical isolates?
E. Faecalis
Virulence factors of Strep. pyogenes (Group A) & brief explanation on how it cause disease
- M proteins: adhere to epithelial cells & resist phagocytosis
- Haemolysin O & S: toxic to cells
- Streptococcal Pyrogenic exotoxins (SPE): toxic shock syndrome, hypotension and shock, scarlet fever
- Enzyme production: (Hyaluronidase) break down CT ground substance = spread
- Hyalorunic acid capsule: adherence & resist phogocytosis
What’s the 1º & 2º infections caused by Strep. pyogenese (group A)?
- 1º: pharyngtitis -> 2º: Rhuematic fever
* 1º: URT infection/scarletfever OR skin/wound infection -> 2º: glomeruar nephritis
Where can you find Strep. agalactiiae (group B)?
- URT
- GIT*
- (female) Genital tract
What is Lancefield groups?
based on carbhydrate “C” antigens/ C substances on cell wall
Explain concept of results of Bile/aesculin slope test?
- no growth, no colour change (green) ≠ tolerate bile (-ve)
- growth, no colour change (green) = tolerate bile, aesculin neg.
- growth, colour change (black) = tolerate bile, aeculin pos
Concept of aesculin hydrolisis test
Aesculin (hydrolised) -> aesculetin (reducing agent) that oxidise Fe3+ (green) to Fe2+ = black (+ve)
Concept of hippurate hydrolysis test
test for hippuricase: Hippuric acid -> glycine oxidised w/ ninhydrin rgnt => purple/blue
