Evidence of Viable But Non-Culturable state in Listeria monocytogenes by direct viable count and CTC-DAPI double staining

Viable but Non-culturable (VBNC) state in bacteria was detected originally in environmental microbiology studies In particular this state has been dem onstrated for a number of human pathogens (Escherichia coli, Salmonella ent eritidis,Vibrio cholerae Legionella pneumophila and Campylobacter jejuni) T he presence of VBNC cells poses a major public health problem since they ca nnot be defected by traditional culturing methods and moreover the cells re main potentially pathogenic under favourable conditions. But the VBNC state has not been yet described in Listeria monocytogenes. Production of VBNC L . monocytogenes cells was studied using four strains resuspended in microco sm water. Various strains of L. monocytogenes were resuspended in filtered sterilized water adjusted to pH 6-0, incubated at 20 degreesC and 4 degrees C with or without NaCl supplementation (0%, 7%), with gentle shaking at 100 rpm. The culturability of starved cells suspensions was determined by spre ad plate count (PCA). The cells activity was measured by a Direct Viable Co unt technique and by CTC-DAPI double staining. Two strains of four (CNL 895 807 Scott A) exhibited a VBNC state. They lost their culturability and main tained a cellular activity, even after 10 weeks of starvation in microcosm water (C) 2000 Academic Press.