Curved, Gram-Negative Bacilli Flashcards
What is the preferred medium of transportation of fecal specimens for V. cholerae ?
Cary-Blair medium
Why is glycerol buffered saline not suitable for fecal specimens of V. cholerae ?
glycerol is toxic to vibrios
What may occur in prolonged cultivation of V. cholerae upon microscopic view ?
vibrios may become straight rods that resemble the Gram-negative enteric bacteria
What is the microscopical characteristics of V. cholerae ?
Gram-negative curved or comma-shaped bacilli, 2–4 μm long
What makes Alkaline Peptone Water (APW) a good enrichment medium for V. cholerae ?
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
Why is the enrichment in Alkaline Peptone Water (APW) of V. cholerae is done when few organisms are present ?
When the patient is in very early stages of illness and is passing liquid stool, it may not be necessary to enrich stool specimens
What is the incubation period for V. cholerae in Alkaline Peptone Water (APW) ?
35°C for 12-18 hours prior to inoculation of plated media
What are the characteristics of V. cholerae in 5% sheep BAM ?
Colonies are typically: medium to large smooth convex creamy in consistency gray-white have entire margins, smooth opaque may be β-hemolytic.
What are the characteristics of V. cholerae in Gelatin agar (GA) ?
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
What is shown when colonies of V. cholerae in GA are viewed in oblique light ?
they appear iridescent green to bronze colored and finely granular
Characteristics of Thiosulfate Citrate Bile Sucrose (TCBS) agar
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
Characteristics of Taurocholate tellurite gelatin agar (TTGA) or Monsur’s agar
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
What is shown when V. cholera is on TCBS ?
slightly flattened
yellow colonies (due to sucrose fermentation)
opaque centers
translucent peripheries
What is shown when V. cholera is on TTGA ?
opaque colonies with slightly dark centers
entire colony becomes “gunmetal” grey in color
surrounded by an opaque zone which resembles a halo
What should be done if there are suspicious colonies required for further testing in TCBS ?
subcultured to a noninhibitory medium: gelatin agar heart infusion agar (HIA) Kligler’s iron agar (KIA) triple sugar iron agar (TSI)
What should be done if there are suspicious colonies required for further testing in TTGA ?
testing should be subcultured to a noninhibitory medium
What is shown when V. cholera is on MAC agar ?
small to moderately sized (1 to 3 mm)
lactose-negative (colorless) or slightly pink
Oxidase test of V. cholera identification, what agar is preferred to be used and to be avoided ?
Conduct the oxidase test with fresh growth from an HIA slant or any non-carbohydrate-containing medium
Do not use growth from TCBS agar
What are the results of V. cholera in TSI agar ?
A/A, no gas, no H2S
Gluc+, Lac-, Suc+
What are the results of V. cholera in KIA agar ?
K/A, no gas, no H2S
Gluc+, Lac-, Suc+
What are the results of V. cholera in the Decarboxylase/Dihydrolase Test ?
LIA: K/K Lysine decarboxylation (+) Ornithine decarboxylation (+) Arginine dihydrolase (-)
What are the results of V. cholera in the string Test ?
positive (+), a long string that becomes more tenacious after 60 seconds or more
What causes there to be a viscous texture in the string test ?
vibrio becomes lysed in 0.5% sodium desoxycholate
suspension will lose turbidity
DNA will be released from the lysed cells, causing a viscous mixture
What are the results of V. cholera in the salt broths ?
V. cholerae grows in nutrient broth base without NaCl, and stimulated by addition of 1.0% NaCl
What does the vibriostatic test use ?
2,4-diamino-6,7-diisopropyl-pteridine phosphate (referred to as O/129)-impregnated disks
What are the results of V. cholera in the vibriostatic test ?
O129-susceptible
What considerations is there in vibriostatic tests ?
recent strains of V. cholerae O1 and V. cholerae O139 have demonstrated resistance; therefore the dependability of this test is questionable
Describe the results and its cause of V. cholera in the cholera red test
(+) result: Red color (due to nitroso indole)
Describe the pfeiffer’s phenomenon
Lysis of V. cholerae organisms when inoculated into immuned guinea pig
Describe the positive reaction of the serological test for V. cholera
Very strong clumping will appear within 30 seconds to 1 minute
What is the principle for the serological test of V. cholera ?
identify V. cholerae O1 serogroup
further subdivide into serotypes, Ogawa, Inaba, and Hikojima by agglutination with specific antisera
