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

CULTURAL AND BIOCHEMICAL PROPERTIES

• The Nocardia species grow very well in blood agar incubated aerobically at 370C for up to 7 days.The colonies on blood agar are often vivid white and powdery if aerial filaments and spores are formed. Occasionally the colonies are smooth, heaped and variably pigmented.
• Inoculate the suspected colonies from blood agar into Sabouraud dextrose agar (SDA) and incubate at 370C for up to 10 days.
• Both types of colonies firmly adherents to the agar surface. The colonies on SDA are dry, wrinkled and yellow, becoming deep orange color with age.
• Gram-stained smears from colonies show Gram-positive branching filaments that characteristically break up into rods or coccobacillary elements with age.
• An MZN –stained smear from young culture reveals red staining, branching filaments.

There are three morphological forms

• Group I strains have limited mycelia development due to early fragmentation of hyphae into coccoid forms within 2 to 14 hours of incubation.
• Group II strains produce mycelia, which fragment in about 18 to 20 hours after incubation, though these mycelia break up into mycelial fragments within two days of growth.
• The pathogenic Nocardia species belong to Group III. The colonies are usually leathery in appearance and pigmented . Extensive mycelium produced because fragmentation does not begin until after 5 days incubation.

Biochemical Properties

• To differentiate Nocardia species tests such as decomposition of casein, hypoxanthine, tyrosine, urea and xanthine are useful.
• They are oxidase and Catalase positive. Reduce nitrates to nitrites. Gelatin not hydrolyzed.