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MBIO 345 > Module 9 > Flashcards

Module 9 Flashcards

1
Q

How many Staph species are there?

A

27

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2
Q

When is lab identification to the species level required?

A

For common human pathogens.

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3
Q

What are the two groups of Staph species and organisms that belong to them?

A

Coagulase positive- S. aureus, S. schleiferi, S. hyicus, S. intermedius

Coagulase negative- S. epidermidis, S. saprophyticus, S. lugdunensis

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4
Q

What is the cellular morphology of Staph?

A

Gram positive cocci

Spherical

0.4-1.2um

Usually clusters

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5
Q

What are the growth requirements of Staph?

A

Facultative anaerobes

Optimum temperature- 35-37°C

Easy to grow, medium can be enriched

No growth on MacConkey

Nonmotile

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6
Q

What is the colonial morphology of Staph?

A

Rapid growth on BAP

Opaque, dense

Varying degrees of B-hemolysis

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7
Q

What are the different types of B-hemolysis?

A

B- complete RBC clearing

a- partial RBC clearing

gamma- no RBC clearing

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8
Q

What is the colonial morphology of S. aureus?

A

Creamy-yellow colonies (lipochrome pigment after 48hrs)

Usually narrow zone of B-hemolysis, some strains show double zone and others are nonhemolytic

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9
Q

What is the colonial morphology of CNS?

A

Usually white

Smaller than S. aureus

Usually gamma hemolytic

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10
Q

What media is used for Staph selection and why?

A

Mannitol salt agar- 7.5% NaCl

Allows staph growth while inhibiting others

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11
Q

How does MSA differentiate between different Staph species?

A

Fermentation of mannitol produces acid that is detected by phenol red.

Growth- Staph

Mannitol negative (red)- CNS

Mannitol positive (yellow)- S. aureus

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12
Q

What is MSA used for?

A

Screening healthcare workers for S. aureus.

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13
Q

What is the genus identification of Staph?

A

Catalase positive

Nitrate positive (after reagent addition)

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14
Q

What is the species identification for S. aureus?

A

Slide coagulase test, detects bound coagulase/clumping factor produced.

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15
Q

What is done if a suspected S. aureus species gives a negative slide coagulase test?

A

Tube coagulase performed.

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16
Q

Why are the two other Staph species that give positive slide coagulase results a nonissue?

A

They are animal isolates.

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17
Q

What does hemagglutination test for?

A

Bound coagulase

Results in immediate clumping of RBCs sensitized with fibrinogen.

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18
Q

How are latex reagents used to test for S. aureus identification?

A

Latex particles are attached to fibrinogen and IgG.

Reacts with the Protein A antibody in S. aureus to produce agglutination.

If protein A (S. aureus) is present, the IgG and latex will be bound.

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19
Q

What is the purpose of the DNase test?

A

Confirmation of S. aureus identification.

Occasional negative test.

4% CNS are positive.

20
Q

What is the purpose of the thermos table nuclease test?

A

Definitive test for S. aureus, only organism that produces the enzyme.

Food microbiology, not routinely performed.

21
Q

When does S. saprophyticus need to be identified down to the species level?

A

When isolated from urine in significant amounts.

22
Q

What is the colonial morphology of S. saprophyticus?

A

1-2mm on BAP, gamma hemolysis, bright white colonies that run together

No growth of MacConkey

Nonmotile

23
Q

What results does S. saprophyticus give on novobiocin susceptibility tests?

A

Resistant zones

Could also be Micrococcus

24
Q

What are the results of a bacitracin test?

A

Staph- resistant

Micrococcus- susceptible

25
Q

What are the characteristics of Micrococcus?

A

Normal skin flora

Grows on BAP- small, nonhemolytic, many colours

Catalase positive

Gram positive

26
Q

What is S. aureus the most common cause of?

A

Skin, soft tissue and post traumatic infections.

Second most acquired hospital infection.

27
Q

What virulence factors does S. aureus produce?

A

Leucocidin

Hyaluronidase

Staphylokinase

Hemolysins

DNase

Coagulase

B-lactamase

28
Q

What common infections are cause by S. aureus?

A

Furuncle (boil)

Carbuncle

Stye

Impetigo

Abscesses (deep soft tissue)

Joint infections

Infected cuts, abrasions, trauma wounds, incisions

Pneumonia

Osteomyelitis

Septicaemia

29
Q

What diseases are caused by S. aureus exotoxins?

A

Food poisoning- heat stable enterotoxin

TSS- grows in tampon

Scalded skin syndrome- mostly children and immunocompromised patients

30
Q

What is the pathogenicity of S. saprophyticus?

A

Primary urinary pathogen.

Mostly young women and older men.

31
Q

What is the pathogenicity of other CNS (not S. saprophyticus)?

A

Normal flora found on skin, nares and genital mucosa.

Opportunistic, leads to generalized infections from shunts, prosthetic heart valves and joints, IV catheters, dialysis procedures.

Septicaemia

Meningitis

UTIs

32
Q

What is the antimicrobial susceptibility of S. aureus?

A

Resistance for penicillin G has increased.

Due to B-lactamase.

33
Q

How is B-lactamase detected in S. aureus?

A

0.5 MF prepared

Inoculated with low concentrations of oxacillin or methicillin.

Growth from edge of zone of inhibition is rubbed on the B-lactamase disc/strip

Resistance can also be determined by antimicrobial susceptibility testing.

34
Q

What antimicrobials is MRSA resistant to?

A

All penicillins and cephalosporins.

Vancomycin is often the only choice in treatment.

35
Q

What makes identifying MRSA difficult?

A

Slow growing

Small colonies that can resemble CNS

May give negative slide coagulase test (requires full 24hrs)

Should perform tube coagulase with in 24hrs

36
Q

What are heteroresistant strains?

A

Those which contain two subpopulations.

S. aureus* has one sensitive to methicillin and one resistant.

37
Q

How is S. aureus detected if it displays heteroresistance?

A

Resistant population grows slower therefore prepared directly.

Incubated at 30-35°C.

2% NaCl to enhance growth.

Oxacillin discs give small zone of inhibition, measure inside irregular growth.

38
Q

Can microdilution and Vitek techniques detect MRSA?

A

No but they may flag possible specimens.

39
Q

What is the screen test for MRSA?

A

MH agar with oxacillin and 4% NaCl.

Spot inoculate and incubate.

Any growth indicates resistance.

40
Q

What new MRSA drugs are there?

A

Linezolid

Quinupristin

Dalfopristin

Daptomycin

Tigecydine

41
Q

What is the antimicrobial susceptibility of CNS species?

A

Generally more resistant.

Mostly normal flora.

42
Q

What is S. saprophyticus normally treated with and why?

A

Less resistant than other CNS.

Treated with quinolones (UTI).

43
Q

What is epidemiology? Give an example.

A

The study of the sources and spread of infection.

Testing hospital workers for S. aureus after an outbreak.

44
Q

What are methods of fingerprinting MRSA isolates?

A

Bacteriophage typing- phages lyse host bacteria, very specific, ID based on lysis patterns

Pulse field gel electrophoresis- cleave chromosome sections and separate on a gel by an electrical current

Mec A gene testing- PCR for gene that codes for resistance to methicillin and other B-lactam antimicrobials

45
Q

What family does the Staph genus belong to?

A

Micrococcaceae

MBIO 345 (11 decks)

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