Some virulent and avirulent pathogenic leptospires and saprophytic leptospires grew continuously at 37°C, while others did not; variations amongst strains of the same serotype occurred and there was no correlation with virulence.

Each of 21 strains survived 24 months' storage in semisolid polysorbate medium (P-80 medium) without intervening subculture and one strain tested after 52 months was still viable and fully virulent. Semisolid and liquid P-80 media had a shelf-life of at least 36 and 12 months respectively at 23–25°C.

One per cent. albumin was shown to favour the survival of leptospires.

In experiments with modified or incomplete semisolid P-80 medium, various leptospiral strains grew and survived when polysorbate, 60,40, or 20 were substituted for polysorbate 80, and when polysorbate, NHCl, thiamine, or vitamin B were omitted. However, the omission of any polysorbate orof vitamin B had a strikingly adverse effect on growth. These modified media were used to culture blood infected withpomona (HCE). Continuous subculture eventually failed to produce readily-detectable macroscopic growth in the absence of either polysorbate, NHCl or thiamine, but continuous subculture in the absence of vitamin B was successful. Nutrient-depleted P-80 media were still capable of maintaining viability and a low level of growth, probably because of the micro-nutrients in the one per cent. albumin component. Continuous subculture of pomona (MU) from hamster liver was successful regardless of the presence of vitamin B in the medium, but vitamin B was essential for similar subculture of the same organism isolated from kidney.


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