Gram pos. cocci

Question 1

2 primary tests that indicate isolate as staphylococcus

Answer 1

1. Catalase : Pos
2. O/F: ferment
3. Oxidase test: Neg

Question 2

What’s the difference b/w plasma & serum?

Answer 2

Serum: No fibrinogen (bc consumed when it clots)
Plasma: anticoagulated fibrinogen available

Question 3

Type of infection S. saprophyticus associated with? & what is given in the Novobiocin test

Answer 3

• Community aquired UTI

- resist novobiocin

Question 4

List 2 virulence factors of S. epidermis

Answer 4

• produce biofilm= resistant to antibiotic & immune resp.
• readily acquires resistance from other bact. (pass plasmids)

Question 5

What does MRSA stand for?

Answer 5

methicillin resistant to Staphylococcus aureus

Question 6

List 4 virulence factors of S. aureus & give e.g. of why or how organism able to cause infection

Answer 6

• 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)

Question 7

What test separates Staphylococci into 2 groups?

Answer 7

Coagulase test
+ve: S. aureus
-ve: S. saprophyticus, S. epidermis

Question 8

Explain theory of coagulase test (how it works)*

Answer 8

• 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

Question 9

Before ID & reporting, what factors of clinical relevance need to be proven for coagulate negative staphylococci (CoNS)?

Answer 9

• Purity of growth
• quantity of growth
• site of infection
• clinical history

Question 10

What type of infections is S. epidermis normally associated w/ & why?

Answer 10

Noscomial infections bc:

• Surgery & implants
• readily acquires resistance from other bact.
• produce biofilm on artificial surfaces => resist antibiotics & immune resp

Question 11

What’s the scientific name for group A streptococcus?

Answer 11

Streptococcus pyogenese

Question 12

What’s the scientific name for group B streptococcus?

Answer 12

Streptococcus agalactiae

Question 13

What antibiotic is the drug of choice used to treat suspected streptococcal pharyngitis?

Answer 13

Pharyngitis from a streptococcal may be from to S. pyogenese = Group A=> Bacitracin sensitive/susceptible

Question 14

What organism would this be? GPC, catalase neg & hippurate pos

Answer 14

Streptococcus agalactiae

Question 15

What organism would this be? GPC, catalase neg & sensitive to Bacitracin

Answer 15

Streptococcus pyogenese

Question 16

How do you differentiate S. pneumoniae & a member of Viridans streptococci?

Answer 16

by Optochin / Bile solubility tests.
S. pneumoniae: susceptible & soluble
Viridans streptococci: reistan & insoluble

Question 17

what’s the reservoir of Strepococcus pyogenes & what area does it inhabit?

Answer 17

a) humnas

b) (mucous membranes) in pharynx (URT)

Question 18

What can Viridans streptococci cause?

Answer 18

Endocardiditis (lead to septacaemia)

Question 19

Which sp. of Enertococcus is common for human clinical isolates?

Answer 19

E. Faecalis

Question 20

Virulence factors of Strep. pyogenes (Group A) & brief explanation on how it cause disease

Answer 20

1. M proteins: adhere to epithelial cells & resist phagocytosis
2. Haemolysin O & S: toxic to cells
3. Streptococcal Pyrogenic exotoxins (SPE): toxic shock syndrome, hypotension and shock, scarlet fever
4. Enzyme production: (Hyaluronidase) break down CT ground substance = spread
5. Hyalorunic acid capsule: adherence & resist phogocytosis

Question 21

What’s the 1º & 2º infections caused by Strep. pyogenese (group A)?

Answer 21

• 1º: pharyngtitis -> 2º: Rhuematic fever

* 1º: URT infection/scarletfever OR skin/wound infection -> 2º: glomeruar nephritis

Question 22

Where can you find Strep. agalactiiae (group B)?

Answer 22

• URT
• GIT*
• (female) Genital tract

Question 23

What is Lancefield groups?

Answer 23

based on carbhydrate “C” antigens/ C substances on cell wall

Question 24

Explain concept of results of Bile/aesculin slope test?

Answer 24

• 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

Question 25

Concept of aesculin hydrolisis test

Answer 25

Aesculin (hydrolised) -> aesculetin (reducing agent) that oxidise Fe3+ (green) to Fe2+ = black (+ve)

Question 26

Concept of hippurate hydrolysis test

Answer 26

test for hippuricase: Hippuric acid -> glycine oxidised w/ ninhydrin rgnt => purple/blue