ID of Gram Positive bacteria

Question 1

You see gram positive cocci in clusters on a stain, what is the likely organism?

Answer 1

Staphlyococcus

Question 2

What are the 2 general characterisitics of all Staphylococci?

Answer 2

Facultative anaerobes, catalase positive

Question 3

What is the catalase test and what organisms does it differentiate between?

Answer 3

Determines if the organism produces catalase which breaks hydrogen peroxide into oxygen and water. Staphylococcus are positive for catalase and strepcoccus and enterococcus are negative.

Question 4

You stain a gram positive cocci in clusters that is slide and tube coagulase positive, what is the organism?

Answer 4

Staphylococcus aureus

Question 5

What organisms are positive for slide coagulase? For tube coagulase?

Answer 5

Slide coagulase: S aureus, S lugdunensis

Tube coagulase: S aureus, S pseudintermedius

Question 6

You isolate a gram positive cocci growing in clusters, its slide coagulase + but tube coagulase negative. It is also PYR test positive, what organism is it?

Answer 6

Staphylococcus lugdunensis

Question 7

What is a staphylococcal species commonly associated with UTIs in women?

Answer 7

Staphylococcus saphrophyticus

Question 8

List four shared characteristics of enterococcal species

Answer 8

1) Growth at 6.5% NaCl at pH 9.6
2) Growth between 10-45 degrees celcius
3) Growth in 40% bile
4) esculin hydrolysis, LAP and PYR positive

Question 9

What 2 enterococcal species are the most common clinical isolates? What antibiotic are they intrinsically resistant to?

Answer 9

Enterococcus faecalis, Enterococcus faecium. Intrinsically resistant to the cephalosporins

Question 10

What are the common characteristics of all streptococcal species?

Answer 10

Gram positive
Grow in pairs or chains
Catalase negative
Facultative anaerobes

Question 11

Describe the difference between alpha, beta and gamma haemolysis. What class of haemolysis do viridans group strep exhibit?

Answer 11

Alpha: partial haemolysis, greening of agar
Beta: Complete haemolysis
Gamma: no haemolysis
Viridans group strep are alpha heamolytic (viridans = green)

Question 12

You isolate a gram positive cocci growing in pairs and chains. It is highly beta heamolytic and taxo A disk (bacitracin) sensitive. What is it?

Answer 12

Streptococcus pyogenes

Question 13

What bacteria predictably susceptible to all beta lactams?

Answer 13

S pyogenes

Question 14

What does the PYR test entail? What bacteria does the PYR test differentiate?

Answer 14

Test for the presence of a specific enzyme
Group A strep and enterococci are PYR positive.
S bovis and other strep are PYR negative

Question 15

What is the purpose of the CAMP test and how does it work? Give an example of a bacteria that would test positive on the CAMP test.

Answer 15

It differentiates group B streptococci from other strep groups. Perform a vertical streak of Staphylococcus aureus on SBA and streak unknown streptococci perpendicular to the staph streak. Synergistic haemolysis in the shape of an arrow head observed for group B strep streaked with staph aureus. Streptococcus agalactiae is a weakly beta haemolytic bug that is CAMP positive.

Question 16

You plate a gram positive diplococci obtained from a brain abscess that is beta haemolytic with pinpoint colonies smelling like butterscotch. Further investigation shows the bacteria in question can be characterized into Group F streptococci, what bacteria must it be?

Answer 16

Streptococcus anginosus group: consists of 3 species

anginosus, intermedius, costellatus

Question 17

What is a simple test to determine whether an unknown streptococci species you have isolated belongs to the bovis group? What is the most commonly clinically isolated bovis group streptococci?

Answer 17

Use the esculin-bile test: streptococcus bovis group will hydrolyze esculin to form a black precipitate. They are also able to grow in the presence of bile.
Streptococcus gallolyticus is the most commonly isolated

Question 18

How would you differentiate streptococcus pneumoniae from other viridans group strep?

Answer 18

S. pneumoniae is bile soluble and optochin sensitive. Other viridans group strep are bile insoluble

Question 19

You have isolated a gram positive bacilli that is beta haemolytic on SBA. You’re pretty sure its Listeria monocytogenes. What further tests would indicate that it is in fact listeria?

Answer 19

Listeria would be catalase and CAMP positive. At 25 degrees it would exhibit tumbling motility and in semi soft agar, umbrella motility. L monocytogenes is intrinsically resistant to the cephalosporins

Question 20

You plate a gram positive bacilli. Under the microscope, the bacteria looks like chinese letters. What group of bacteria could this be?

Answer 20

Corynebacterium spp.