Bacteriology (Gram Positives Cocci)

Front 1

Which statement is false regarding a kirby bauer plate?
A. A 100mm plate can hold 7 discs.
B. A 150mm plate can hold 12 discs
C. Discs should be at least 15mm from the edge
D. Discs should be at least 24mm apart
E. The measurements can not be made on the under surface of the plate.

Back 1

E. A-D are correct and have appear on board exams by means of picture (what is wrong with this picture). The measurements CAN be made with a ruler on the under surface of the plate without opening the lid. The endpoint of inhibition is judged by the naked eye at the edge where the growth starts. Certain Proteus species may swarm into the area of inhibition around some antibiotics, but the zone of inhibition is usually clearly outlined and the thin layer of swarming growth should be ignored.

Front 2

What is the order of chemicals in a gram stain?
Alcohol
Crystal violet
Iodine
Safranin

Back 2

Crystal violet
Iodine
Alcohol (decolorizer)
Safranin

Front 3

How many epithelial cells (at 10x) will is considered inadequate for sputum?

Back 3

25+

Note: this only disqualifies bacterial culture, not AFB or fungus

Front 4

What test of the CSF can be useful for detecting bacteria in partially treated patients suspected to have a bacterial meningitis?

Back 4

Latex agglutination test

Front 5

What antigen does the slide coagulase test versus the tube coagulase?

Back 5

The slide coagulase tests for bound coagulase.

The tube coagulase tests for free coagulase.

Front 6

Mannitol salt agar with gram (+), catylase (+) bacteria. What is the organism on the right?
A. Strep pneumo
B. Staph Aureus
C. Staph Saproph.
D. Micrococcus

Back 6

Staph Aureus - turns yellow on mannitol salt agar; can be used in place of coagulase.
-Assuming the same initial I.D, the stuff on the left is coag negative staph or micrococcus.

Front 7

Novobiocin resistant, coagulase negative staphylococcus?
A. Strep pneumo
B. Staph Aureus
C. Staph Saproph.
D. Micrococcus

Back 7

Staph saprophyticus (in contrast to the other coagulase negatative staph which are sensitive to novobiocin)

- Causes UTI's in child bearing aged females

Front 8

This is a coagulase negative staphylococcus on blood agar. What is the most likely diagnosis?

Back 8

Staph hemolyticus

- The other coagulase negative staphs are not hemolytic.

Front 9

Name the organism. The disk on the right is Novobiocin. The organism is Gram (+), catylase (+), and coagulase (-)

Back 9

Staph saprophyticus (in contrast to the other coagulase negatative staph which are sensitive to novobiocin)

- UTI's in child bearing age femailes. Adheres well to epithelial cells

Front 10

Gram +: name the organsm

Back 10

Micrococcus (luteus or lylae)
cocci in tetrads
-normal flora, only rarely infectious

Front 11

If a slide coagulase test is negative, what is the follow-up test?

Back 11

Tube coagulase

Front 12

What test would be most helpful to differentiate this organism from staph aureus?

Back 12

Mircodase (modified oxidase rxn)
Micrococcus = positive

Or bacitracin (micrococcus is sus.)

Front 13

Gram + cocci in clusters that is sticky, mucoid white and is adherent to the agar.

Back 13

Rothia mucilaginosa

Front 14

Gram positive, catalase negative cocci. Alpha hemolytic. What is the next appropriate test?

Back 14

Is strep pneumoniae vs. strep viridans/abiotrophia. Do optochin. Strep pneumoniae is optochin sensitive.

Front 15

What causes the greening seen in alpha hemolysis?

Back 15

Caused by hydrogen peroxide production by the bacterium, oxidizing hemoglobin to green methemoglobin.

Front 16

What is the Lancefield grouping system based upon?

Back 16

The C carbohydrate in the cell wall

Front 17

What members of the Streptococcaceae family will give a positive PYR test?

Back 17

Group D Enterococci and Streptococcus pyogenes (Group A)

Front 18

What is the name and use for this test?

Back 18

CAMP test - Staph aureus causes increased toxin production by group B strep.
This arrow is seen in Strep agalactiae (group B), deferentiating it from strep pyogenes (group A). (can also used PYR instead)

Front 19

Gram positive cocci, catalase (-), beta hemolytic. What is it (right side)?

Back 19

This is a positive PYR which makes this strep pyogenes (group A). strep agalactiae (group B) would be PYR negative. You put the organism on it, warm it, and "develop" it with cynameldahyde. One can also use CAMP for this differential.

Front 20

Bacitracin disc. What type of streptococcus is this?

Back 20

S. agalactiae (resistant to bacitracin). This is in contrast to S. pyogenes which is sensitive to bacitracin.

Front 21

What gram positive organism is optochin sensitive?

Back 21

Strep pneumoniae

Front 22

How do you detect penicillin resistance in strep pneumonia?

Back 22

An oxacillin disk is read. It must read 20 mm or greater to be susceptible to penicillin.

Front 23

Gram (+), catalase (-), gamma hemolytic cocci. 2 tests can be used next to differentiate enterococcus from Group D, what are they?

Back 23

Enterococcus Group D
PYR + PYR -
6.5% salt + 6.5% salt -

Front 24

What test is used to differentiate enterococcus facium from fecalis?

Back 24

Faecium - Arabinose positive
Faecalis- Arabinose negative

Front 25

What strep organisms are BEA (bile esculin) positive?

Back 25

-Group D strep (bovis)
-enterococcus
(both are gamma hemolytic)

Front 26

Name the organism.

Back 26

Strep pneumoniae

Bile soluble, optochin sensitive (>14mm)
Polysaccharide capsule

Front 27

What type of strep species is bile soluble?

Back 27

Strep pneumoniae

Drop sodium deoxycholate on the colony and it disappears

Front 28

What is this gram positive, alpha hemolytic organism?

Back 28

This is an optochin disc (p), if >14mm diameter zone around disc, then this is a strep pneumoniae

Front 29

Gram +, alpha hemolytic. What is the organism?

Back 29

This is an optochin disc. Since the organism is resistant <14mm, then this is strep viridans or abiotrophia (not strep pneumonia).

Viridans are also bile non-soluble vs. pneumoniae

Front 30

Species of strep that will only grow next to staph aureus?

Back 30

Abiotrophia or globicatella (nutritionally variant strep). Alpha-hemolytic, optochin resistant. Need B6 to grow. Cause endocarditis and are more resistant to antibiotics. Note: Hemaphilus has similar phenom

Front 31

Staph Aureus streak. What is the organism growing around it (gram +)?

Back 31

Nutritionally variant Strep
-Abiotrophia defectiva
-Globicatella adiacens
(needs vit B6)

Front 32

Which two gram positive cocci are bacitracin sensitive?

Back 32

Micrococcus (vs. staph aureus)
Strep pyogenes (vs. S. agalactiae