Biochemical tests

Question 1

What is the first test usually used to differentiate gram positive organisms

Answer 1

Catalase test –> positive in Micrococcaceae (Staph and Micrococci) and negative in streptococci

Question 2

Furazolidone susceptibility

Answer 2

Used to distinguish susceptible Staph from non-susc Micrococci

Question 3

What test is used to differentiate S. aureus from other Staph?

Answer 3

Coagulase test: coagulase has prothrombin like activity that converts fibrinogen to fibrin

Question 4

When should the tube coagulase test be performed?

Answer 4

When insufficient colonies of Staph is present and the slide test is negative at 30 seconds.

Question 5

Technique for tube coagulase tube test

Answer 5

The tube must be examined at 4 and 20 hours because some strains have fibrinolysin that will dissolve a formed clot and give a false negative if not checked at 4 hours. Others may have a delayed reaction and be negative at 4 hours.

Question 6

What test is used to distinguish among coagulase negative Staph?

Answer 6

Novobiocin susceptibility
Susceptible: S. epidermidis
Resistant: S. saprophyticus

Question 7

What method is used to differentiate between B-hemolytic streptococci?

Answer 7

(A disc) Bacitracin & TMP-SMX susceptibility
Group B strep (agalactiae): Resistant to both
Group A Strep (pyogenes): resistant to TMP-SXT but sensitive to bacitracin
Other B-hemolytic strep: susc to both

Question 8

What test is used to separate group D enterococci from group D non-enterococci?

Answer 8

6.5% NaCl tolerance
Enterococcus spp: salt tolerant
Group D (S. bovis): not salt tolerant

Question 9

What is the CAMP test?

Answer 9

used to identify group B strep by plating it next to staph aureus, B-hemolysin in the staph is enhanced due to the CAMP factor in the GBS
Most other hemolytic strep do not have CAMP factor

Question 10

What test can replace the bacitracin and salt tolerance tests for identifying Group A and D strep?

Answer 10

PYR test

Aminopeptidase produced by these bacteria hydrolyzes PYR which yields a red color

Question 11

What is the bile esculin test?

Answer 11

Used to identify enterococcus and Group D not enterococci (S. bovis), both can grow in bile and hydrolyze esculin–> Diffuse blackening of more than half the slant after streaking and incubating for 24 hrs

Question 12

How is the optochin disk (P) used?

Answer 12

It selectively inhibits S. pneumo

Question 13

What organism is bile soluble??

Answer 13

S. pneumo

Question 14

What organisms are oxidase negative?

Answer 14

Enterobacteriaceae

Question 15

What organisms are oxidase positive?

Answer 15

Vibronaceae, Aeromonas, Neisseria, Pseudomonas, Campylobacter and Pasteurella

Question 16

What organism is indole + and lactose +?

Answer 16

E. coli

Question 17

What organisms reduce nitrate to nitrite?

Answer 17

Enterobacteriaceae

Question 18

What is the purpose of Hugh-Leifson OF medium?

Answer 18

oxidative-fermentative test is used to determine if gram-negative bacteria metabolize carbohydrates oxidatively, by fermentation, or are nonsacchrolytic and therefore have no ability to use the carbohydrate in the media.

Question 19

How do you interpret Hugh-Leifson OF medium?

Answer 19

Yellow= acid production
Yellow only in open tube=oxidative organism
Yellow in both tubes= fermenting organisms
green in both tubes/ blue in open tube=nonsaccharolytic organism

Question 20

What is the string test?

Answer 20

Diffferentiates V. cholera because the string becomes more tenacious with time as opposed to others vibrio that have an initial string which diminishes in 60 seconds

Question 21

What organism satellites around a streak of S aueus and why?

Answer 21

Haemophilus spp. because of the ability of S aureus to synthesize V factor and to release X factor by lysing blood.

Question 22

Which Haemophilus utilizes only V factor?

Answer 22

H parainfluenzae, H parahaemolyticus, H aphrophilus (P’s need the V’s)

Question 23

Which Haemophilus spp utilizes only X factor?

Answer 23

H. ducreyi (X-rated transmission)

Question 24

Which Haemophilus spp utilizes X & V factor?

Answer 24

H. influenza, H haemolyticus and H aegyptius

Question 25

Which Neisseria spp utilizes only glucose?

Answer 25

N. gonorrhae

Question 26

Which Neisseria spp utilizes glucose and maltose?

Answer 26

N meningitides

Question 27

Which Neisseria spp utilizes glucose, maltose and sucrose?

Answer 27

N sicca

Question 28

Which Neisseria spp utilizes glucose, maltose and lactose?

Answer 28

N lactamica

Question 29

Which organism is negative for all sugars on CHO utilization testing?

Answer 29

Moraxella catarrhalis

Question 30

What is the superoxol test used for?

Answer 30

For the rapid, presumptive diagnosis of N gonorrhea. Superoxol is 30% H202, not the usual 3% used for the catalase test

Question 31

Which gram- coccus produces DNAse?

Answer 31

Moraxella catarrhalis