Systematic Veterinary Bacteriology and Mycology

Cultural characteristics

CUTURAL CHARACTERISTICS

• Growth is scanty on ordinary media. Enrichment with blood, serum or egg is necessary for good growth. The optimum temperature for growth is 37ºC and optimum pH is 7.2. It is an aerobe and facultative anaerobe. Sheep or ox blood agar is used routinely along with MacConkey agar to detect any Gram-negative contaminants that may be present.

• On blood agar, Corynebacterium ovis colonies are small, white, dry and non-haemolytic at 24hr incubation.
• A narrow zone of haemolysis occurs at 72 hrs incubation. After several days incubation the colonies can reach 3mm in d.m and appear dry, crumbly and cream in color.
  Corynebacterium bovis colonies are small, white, dry and non-haemolytic.
• As it is a lipophilic corynebacterium, they grow very well on media enriched with 0.5 –1% tween 80.
• Rhodococcus equi colonies are small, smooth, shiny and non-haemolytic after 24 hrs incubation. But on 4-day culture, the colonies become larger, mucoid and salmon-pink in color.
• The salmon-pink pigmentation is not easily seen against a red background.
• So, the mucoid colonies and salmon-pink pigmentation can easily be demonstrated on nutrient agar (4-day culture).
• Nutrient agar enriched with yeast extract and glucose is useful for enhancing the salmon pink pigmentation.
• The renale groups are non-haemolytic. On nutrient agar, after 48 hrs incubation, Corynebacterium renale produces dull yellow colonies.
• The Corynebacterium pilosum produces distinct yellow and Corynebacterium cystitidis exhibit white colonies.
• On milk agar, Corynebacterium renale showing casein digestion. While Corynebacterium pilosum and Corynebacterium cystitidis do not give this reaction.
• On CAMP tests, the Corynebacterium ovis, Rhodococcus equi and Corynebacterium renale interacting with beta haemolytic strains of Staphylococcus aureus gives the following results.

	Staphylococcal beta haemolysis
Corynebacterium ovis	Inhibition
Rhodococcus equi	Enhancement
Corynebacterium renale	Enhancement