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

CULTURAL CHARACTERISTICS

• Leptospira are obligate aerobes that use long chain fatty acids or fatty alcohols rather than CHO and aminoacid as their energy and carbon sources.
• In addition to this it also requires vitamins B1, B12 and purines. Optimum temperature for growth is 25ºC to 35ºC. They are highly fastidious.
• They grow very well in media enriched with rabbit plasma (rabbit plasma contain high concentration of bound vitamin B₁₂).
• Several liquid and semisolid media are available. Korthof’s modified medium, Stuart’s liquid medium, Fletcher’s semi solid medium, EMJH (Ellinghausen, McCullough (1965), Johnson and Harris (1967), protein free medium (commomly used for preparation of vaccine) and Ellis medium (mainly for isolation of leptospires from the genital tract of cows).
• Among these, the EMJH medium contains bovine albumin (fraction V), Tween 80 and rabbit plasma and is most commonly used for isolation of Leptospira.
• The generation time in laboratory media is 12 –16 hrs. The cultures are incubated at 30ºC for upto 8 weeks.
• In semisolid media, growth occurs characteristically a few millimeters below the surface.
• Addition of 5-flurouracil (100 mgm/ml) in medium is inhibitory for most of the microorganism but not for leptospires.
• The colonies of Leptospira strains appear colorless and below the surface of the agar. They may not be visible until held against opaque light.
• The leptospires are identified on the basis of their typical morphology and motility under dark field microscopy.
• In fluid medium, the leptospires appear to rotate alternatively along their axis, moving backward and forward with no apparent polar differentiation.
• In semisolid media, flexing, boring and serpentine movements are seen.