Virulence characteristics of food processing relevance in isolates of Listeria monocytogenes and Escherichia coli 0157: H7 strains isolated from 'wara' a West African soft cheese

Abstract

Three strains of Escherichia coli 0157:H7 and eleven strains of Listeria monocytogenes isolated from West African wara cheese were analysed for cellulose production, fimbriae formation, zetapotential and biofilm formation which are of relevance in food processing. E. coli c produced no fimbria, very low cellulose and significantly lower zetapotential (-3.1) among the three strains. The L. monocytogenes (b) had the highest zetapotential (-39.1) and cellulose production at 24 h of incubation. Next to it was L. monocytogenes (f) which also had a higher cellulose production at 72 h incubation. A positive correlation exists between zetapotential and cellulose production in the E. coli strains (R2 = 0.67) while Listeria monocytogenes strains gave a negative correlation (R2 = -0.08). There was no significant difference in biofilm formation in the L. monocytogenes strains (P < 0.05), however the L. monocytogenes (a) had the highest at 48 h incubation. Weak positive correlation (R²) values of 0.0397, 0.002 and 0.0011 were obtained for 24, 48 and 72 h incubation for Listeria monocytogenescounts (cfu/ml) and cellulose measurements. This study further accentuate and confirmed the presence of E. coli and L. monocytogenes with virulent factors that of relevance to the method of processing in West African soft cheese. The need for an improved hygiene during processing and sale of this product to prevent the transmission of these pathogenic organisms to humans is therefore emphasized. Key words: West African soft cheese, Escherichia coli, Listeria monocytogenes,virulent strains