Module 9

Question 1

What happens if we isolate Staph from urine?

Answer 1

We must do further testing to find out if it is Staph saprophyticus

Question 2

New MRSA drugs

Answer 2

Linezolid, Quinupristin, Dalfopristin

Question 3

Virulence factors present in Staph aureus

Answer 3

Leucocidin (kills phagocytic white blood cells)
Hyaluronidase
Staphylokinase
Hemolysins
DNase
Coagulase
Beta-lactamase production

Question 4

Impetigo

Answer 4

Superficial skin infection, watery blisters, communicable especially among children

Question 5

Common Staph aureus infections

Answer 5

Furuncle (boil), carbuncle, stye, impetigo, abscesses, joint infections, infected cuts/abrasions/wounds/incisions, pneumonia, osteomyelitis, septicemia

Question 6

Beta hemolysis

Answer 6

Complete clearing of RBCs around colony

Question 7

Alpha hemolysis

Answer 7

Partial clearing of RBCs, greening around colony

Question 8

Gamma hemolysis

Answer 8

No hemolysis - no clearing of RBCs around colony

Question 9

Mannitol salt agar (MSA)

Answer 9

Contains 7.5% sodium chloride

Selective media for isolation of Staphylococci; inhibits growth of most other bacteria

Question 10

Growth on MSA indicates:

Answer 10

Likely a Staphylococcus

Question 11

Mannitol negative (red) colonies on MSA indicate:

Answer 11

Likely a coagulase negative Staphylococcus

Question 12

Mannitol positive (yellow) colonies on MSA indicate:

Answer 12

Likely S. aureus

Question 13

2 tests that can be used for genus identification (Staph)

Answer 13

Catalase test

Nitrate test

Question 14

Family that Staphylococcus is in

Answer 14

Micrococcaceae

Question 15

Growth requirements for Staphylococcus

Answer 15

Facultative anaerobes: grow better in air than anaerobic conditions
Opt. temperature = 35-37 C
Grows easily on most media

Question 16

Motility of Staphylococcus

Answer 16

Non motile, no flagella, atrichous

Question 17

Colonial morphology of Staph on BAP

Answer 17

Overnight colonies are 1-4 mm in size
Opaque, unable to see through colonies, not transparent, “vanilla pudding”
Narrow zone of beta hemolysis may be seen = complete destruction of blood cells below the Staphylococcus colony on blood agar plate or no hemolysis (gamma)
Double zone of hemolysis may also be seen
Some strains are non-hemolytic

Question 18

Pigmentation of Staph aureus colonies on BAP

Answer 18

Creamy yellow color of colonies increases with increased incubation time due to Lipochrome pigment.
May take 48-72 hours to develop yellow color

Question 19

Colonial morphology of CNS on BAP

Answer 19

Coagulase negative Staphylococcus colonies are usually white, small, opaque and gamma or non-hemolytic

Question 20

% salt content in MSA

Answer 20

7.5%

Question 21

Growth on MSA

Answer 21

Growth on MSA = Staphylococcus
Mannitol negative (red) = Coagulase negative Staphylococcus
Mannitol positive (yellow) = most likely S. aureus

Question 22

Genus ID for Staph

Answer 22

Perform the Catalase test (most commonly used) or perform Nitrate test

Question 23

Species ID for Staph

Answer 23

After performing genus test, do we have S. aureus or Coagulase Negative Staphylococcus?
Perform the Coagulase test: slide coag first, tube coag if needed
We are testing bacterial colonies for the presence of these enzymes = positive or negative test results

Question 24

Tube coagulase is the best single identification test for:

Answer 24

S.aureus

Question 25

Staphylococcus saprophyticus identification

Answer 25

Novobiocin susceptibility test Spread 0.5 McFarland turbidity of Staphylococcus isolate on BAP or MH plate Add Novobiocin disc (an antimicrobial disc used for bacterial identification) Incubate overnight Read and measure zone size Staphylococcus saprophyticus is resistant to Novobiocin and may grow right up to disc (zones of 12mm or less are resistant, = 12 mm) Other CNS have a zone of inhibition > 12 mm

Question 26

Most commonly isolated species of CNS from clinical material

Answer 26

Staphylococcus epidermidis

Question 27

Colonial morphology of S. epidermidis on BAP

Answer 27

Opaque, white, non hemolytic

Question 28

What can enhance typical S. aureus pigmentation?

Answer 28

Incubating 18hrs at 35C, then a further 18hrs at room temp

Question 29

The most reliable single test for identification of S. aureus

Answer 29

Tube coagulase

Question 30

Protein A in S. aureus

Answer 30

A cell wall protein Combines with the Fc part of IgG Can be detected by reaction with IgG attached to latex particles

Question 31

A test useful for detecting S. aureus directly from filtrates of food

Answer 31

Thermostable nuclease

Question 32

Test that differentiates the genus Staphylococcus from Micrococcus

Answer 32

Resistance to bacitracin

Question 33

3 diseases that can be caused by an exotoxin of S aureus

Answer 33

Toxic shock syndrome, food poisoning, scalded skin syndrome

Question 34

NCCLS recommended procedure for detecting MRSA

Answer 34

Oxacillin agar screen test

Question 35

Usual drug used to treat patients with MRSA infections

Answer 35

Vancomycin

Question 36

Tests used for epidemiological studies of MRSA outbreaks

Answer 36

Bacteriophage typing, pulse-field gel electrophoresis

Question 37

What percentage of S. aureus isolates are resistant to Penicillin?

Answer 37

85-90%

Question 38

When do symptoms for Staphylococcal food poisoning usually occur?

Answer 38

Within 1-6 hours

Question 39

Bacteriophage

Answer 39

Viruses that attack specific bacteria | Host-specific