Abstract

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Haemolysin (Listeriolysin O) is a major virulence factor in pathogenic strains of Listeria. Presently, the conditions for its production are not fully elucidated. This study examined the influence of culture pH and temperature on cell viability, multiplication and haemolysin production by fresh isolates of L. monocytogenes, L. ivanovii and L. seeligieri. At 5oC and pH 3.8 to 4.8, there was a significant (p < 0.05) decline in cell viability and multiplication. However, both parameters remained in a steady state from pH 5.0 to 5.6 at the same temperature. At 30oC, there was also decline in cell viability and multiplication from pH 3.8 to 4.8 but significant cell multiplication from pH 5.0 to 5.6. Haemolysin production was concomitant with conditions allowing growth of the listerial organisms and the highest increases in haemolysin production were recorded during the log phase of growth. For all isolates, haemolysin was produced from pH 5.0 to 9.0 at the above temperatures and productivity was highest with L. ivanovii.

Keywords: Listeria monocytogenes; L. ivanovii; haemolysin; pH; temperature