Curved, Gram-Negative Bacilli

Question 1

What is the preferred medium of transportation of fecal specimens for V. cholerae ?

Answer 1

Cary-Blair medium

Question 2

Why is glycerol buffered saline not suitable for fecal specimens of V. cholerae ?

Answer 2

glycerol is toxic to vibrios

Question 3

What may occur in prolonged cultivation of V. cholerae upon microscopic view ?

Answer 3

vibrios may become straight rods that resemble the Gram-negative enteric bacteria

Question 4

What is the microscopical characteristics of V. cholerae ?

Answer 4

Gram-negative curved or comma-shaped bacilli, 2–4 μm long

Question 5

What makes Alkaline Peptone Water (APW) a good enrichment medium for V. cholerae ?

Answer 5

1% (w/v) sodium chloride incorporated in this medium promotes the growth of Vibrio species

The alkalinity (pH 8.6) of this medium inhibits most of the commensal intestinal bacteria

Question 6

Why is the enrichment in Alkaline Peptone Water (APW) of V. cholerae is done when few organisms are present ?

Answer 6

When the patient is in very early stages of illness and is passing liquid stool, it may not be necessary to enrich stool specimens

Question 7

What is the incubation period for V. cholerae in Alkaline Peptone Water (APW) ?

Answer 7

35°C for 12-18 hours prior to inoculation of plated media

Question 8

What are the characteristics of V. cholerae in 5% sheep BAM ?

Answer 8

Colonies are typically: 
medium to large
smooth
convex
creamy in consistency
gray-white
have entire margins,
smooth
opaque
may be β-hemolytic.

Question 9

What are the characteristics of V. cholerae in Gelatin agar (GA) ?

Answer 9

Colonies appear transparent

usually have a characteristic cloudy or opaque zone (due to gelatinase activity) around colony, which becomes more definite after few minutes of refrigeration

Question 10

What is shown when colonies of V. cholerae in GA are viewed in oblique light ?

Answer 10

they appear iridescent green to bronze colored and finely granular

Question 11

Characteristics of Thiosulfate Citrate Bile Sucrose (TCBS) agar

Answer 11

1% Sodium chloride stimulates growth of Vibrio species

Saccharose (sucrose) is included as a fermentable carbohydrate

Bile salts (oxgall) inhibit gram-positive bacteria
alkaline pH (8.6) of the medium inhibits most of the commensal intestinal bacteria

Question 12

Characteristics of Taurocholate tellurite gelatin agar (TTGA) or Monsur’s agar

Answer 12

Sodium taurocholate inhibits the contaminating gram-positive bacteria
Potassium tellurite is a selective and differential agent It inhibits many gram-positive
Sodium carbonate inhibits most Enterobacteriaceae and gram-positive bacteria

Gelatin acts as an additional carbon and energy source causes the halo effect

Question 13

What is shown when V. cholera is on TCBS ?

Answer 13

slightly flattened
yellow colonies (due to sucrose fermentation)
opaque centers
translucent peripheries

Question 14

What is shown when V. cholera is on TTGA ?

Answer 14

opaque colonies with slightly dark centers
entire colony becomes “gunmetal” grey in color
surrounded by an opaque zone which resembles a halo

Question 15

What should be done if there are suspicious colonies required for further testing in TCBS ?

Answer 15

subcultured to a noninhibitory medium:
gelatin agar
heart infusion agar (HIA)
Kligler’s iron agar (KIA)
triple sugar iron agar (TSI)

Question 16

What should be done if there are suspicious colonies required for further testing in TTGA ?

Answer 16

testing should be subcultured to a noninhibitory medium

Question 17

What is shown when V. cholera is on MAC agar ?

Answer 17

small to moderately sized (1 to 3 mm)

lactose-negative (colorless) or slightly pink

Question 18

Oxidase test of V. cholera identification, what agar is preferred to be used and to be avoided ?

Answer 18

Conduct the oxidase test with fresh growth from an HIA slant or any non-carbohydrate-containing medium

Do not use growth from TCBS agar

Question 19

What are the results of V. cholera in TSI agar ?

Answer 19

A/A, no gas, no H2S

Gluc+, Lac-, Suc+

Question 20

What are the results of V. cholera in KIA agar ?

Answer 20

K/A, no gas, no H2S

Gluc+, Lac-, Suc+

Question 21

What are the results of V. cholera in the Decarboxylase/Dihydrolase Test ?

Answer 21

LIA: K/K
Lysine decarboxylation (+)
Ornithine decarboxylation (+)
Arginine dihydrolase (-)

Question 22

What are the results of V. cholera in the string Test ?

Answer 22

positive (+), a long string that becomes more tenacious after 60 seconds or more

Question 23

What causes there to be a viscous texture in the string test ?

Answer 23

vibrio becomes lysed in 0.5% sodium desoxycholate

suspension will lose turbidity

DNA will be released from the lysed cells, causing a viscous mixture

Question 24

What are the results of V. cholera in the salt broths ?

Answer 24

V. cholerae grows in nutrient broth base without NaCl, and stimulated by addition of 1.0% NaCl

Question 25

What does the vibriostatic test use ?

Answer 25

2,4-diamino-6,7-diisopropyl-pteridine phosphate (referred to as O/129)-impregnated disks

Question 26

What are the results of V. cholera in the vibriostatic test ?

Answer 26

O129-susceptible

Question 27

What considerations is there in vibriostatic tests ?

Answer 27

recent strains of V. cholerae O1 and V. cholerae O139 have demonstrated resistance; therefore the dependability of this test is questionable

Question 28

Describe the results and its cause of V. cholera in the cholera red test

Answer 28

(+) result: Red color (due to nitroso indole)

Question 29

Describe the pfeiffer’s phenomenon

Answer 29

Lysis of V. cholerae organisms when inoculated into immuned guinea pig

Question 30

Describe the positive reaction of the serological test for V. cholera

Answer 30

Very strong clumping will appear within 30 seconds to 1 minute

Question 31

What is the principle for the serological test of V. cholera ?

Answer 31

identify V. cholerae O1 serogroup

further subdivide into serotypes, Ogawa, Inaba, and Hikojima by agglutination with specific antisera