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32 Cards in this Set

  • Front
  • Back
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.
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.
What is the order of chemicals in a gram stain?
Crystal violet
Crystal violet
Alcohol (decolorizer)
How many epithelial cells (at 10x) will is considered inadequate for sputum?

Note: this only disqualifies bacterial culture, not AFB or fungus
What test of the CSF can be useful for detecting bacteria in partially treated patients suspected to have a bacterial meningitis?
Latex agglutination test
What antigen does the slide coagulase test versus the tube coagulase?
The slide coagulase tests for bound coagulase.

The tube coagulase tests for free coagulase.
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
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.
Novobiocin resistant, coagulase negative staphylococcus?
A. Strep pneumo
B. Staph Aureus
C. Staph Saproph.
D. Micrococcus
Staph saprophyticus (in contrast to the other coagulase negatative staph which are sensitive to novobiocin)

- Causes UTI's in child bearing aged females
This is a coagulase negative staphylococcus on blood agar. What is the most likely diagnosis?
Staph hemolyticus

- The other coagulase negative staphs are not hemolytic.
Name the organism. The disk on the right is Novobiocin. The organism is Gram (+), catylase (+), and coagulase (-)
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
Gram +: name the organsm
Micrococcus (luteus or lylae)
cocci in tetrads
-normal flora, only rarely infectious
If a slide coagulase test is negative, what is the follow-up test?
Tube coagulase
What test would be most helpful to differentiate this organism from staph aureus?
Mircodase (modified oxidase rxn)
Micrococcus = positive

Or bacitracin (micrococcus is sus.)
Gram + cocci in clusters that is sticky, mucoid white and is adherent to the agar.
Rothia mucilaginosa
Gram positive, catalase negative cocci. Alpha hemolytic. What is the next appropriate test?
Is strep pneumoniae vs. strep viridans/abiotrophia. Do optochin. Strep pneumoniae is optochin sensitive.
What causes the greening seen in alpha hemolysis?
Caused by hydrogen peroxide production by the bacterium, oxidizing hemoglobin to green methemoglobin.
What is the Lancefield grouping system based upon?
The C carbohydrate in the cell wall
What members of the Streptococcaceae family will give a positive PYR test?
Group D Enterococci and Streptococcus pyogenes (Group A)
What is the name and use for this test?
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)
Gram positive cocci, catalase (-), beta hemolytic. What is it (right side)?
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.
Bacitracin disc. What type of streptococcus is this?
S. agalactiae (resistant to bacitracin). This is in contrast to S. pyogenes which is sensitive to bacitracin.
What gram positive organism is optochin sensitive?
Strep pneumoniae
How do you detect penicillin resistance in strep pneumonia?
An oxacillin disk is read. It must read 20 mm or greater to be susceptible to penicillin.
Gram (+), catalase (-), gamma hemolytic cocci. 2 tests can be used next to differentiate enterococcus from Group D, what are they?
Enterococcus Group D
6.5% salt + 6.5% salt -
What test is used to differentiate enterococcus facium from fecalis?
Faecium - Arabinose positive
Faecalis- Arabinose negative
What strep organisms are BEA (bile esculin) positive?
-Group D strep (bovis)
(both are gamma hemolytic)
Name the organism.
Strep pneumoniae

Bile soluble, optochin sensitive (>14mm)
Polysaccharide capsule
What type of strep species is bile soluble?
Strep pneumoniae

Drop sodium deoxycholate on the colony and it disappears
What is this gram positive, alpha hemolytic organism?
This is an optochin disc (p), if >14mm diameter zone around disc, then this is a strep pneumoniae
Gram +, alpha hemolytic. What is the organism?
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
Species of strep that will only grow next to staph aureus?
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
Staph Aureus streak. What is the organism growing around it (gram +)?
Nutritionally variant Strep
-Abiotrophia defectiva
-Globicatella adiacens
(needs vit B6)
Which two gram positive cocci are bacitracin sensitive?
Micrococcus (vs. staph aureus)
Strep pyogenes (vs. S. agalactiae