VMC 311: Systematic Veterinary Bacteriology and Mycology (2+1)

STAINING CHARACTER AND CULTURAL CHARACTERS

Staining character

• Short Gram-positive rods or coccobacilli are seen at 24 hours of incubation.

Cultural characters

• The organism is frequently difficult to recover from the brain in neural Listeriosis (circling disease), presumably because the organisms are intracellular and present in small numbers.
• If no growth is obtained initially, ground brain should be stored at refrigeration temperature at 4⁰C (cold enrichment) and recultured weekly for as long as 12 weeks before it is discarded as negative.
• The organism grows well on ordinary media but is routinely isolated on blood agar. Primary growth is stimulated by 5-10% CO2.
• Smooth colonies are approximately 2 mm in diameter, round, entire, glistening, bluish by transmitted light, and narrow zones of beta hemolysis are evident.

Biochemical properties of Listeria monocytogenes

Catalase	+	H2S	-
Oxidase	-	Indole	-
MR	+	Aesculin	+
VP	+	CAMP	+

• It shows the characteristic tumbling motility when a 2-4 hours glucose phosphate broth culture is incubated at 25°C.
• When grown in semisolid motility media, the Listeria species give an umbrella shaped growth in the subsurface.
• Acid produced from rhamnose , but not from xylose.

Animal Inoculation test for Listeria monocytogenes

• Mice, Rabbits and Guinea pigs are susceptible to Listeria Monocytogenes.
• A Kerato conjunctivitis (Anton’s test) is produced by Listeria monocytogenes within 24 hours after the instillation of organisms into the eyes of Guinea pigs and rabbits.