Abstract:

Objective: The virulence-associated genes of Listeria monocytogenes (L.m) isolates were detected by PCR amplification assay in order to provide experimental references for evaluating the virulence of L.m isolates and effectively limiting the transmission of L.m. Methods: Forty strains of L.m isolated in Chongqing from 2007 to 2009 were subjected to the PCR detection of seven virulence-associated genes (hly, plcB, inlA, inlB, inlC, inlJ, prfA) and toxicity test in mice. Results: The PCR assay revealed that 15 of the 40 L.m isolates possessed all the seven virulence-associated genes, 6 strains were hly-, 4 strains were plcB-,4 strains were prfA- , 5 strains were inlA-, inlB-, 11 strains were inlC -, 9 strains were inlJ -, and 1 strain was negative for inlA, inlB, inlC and inlJ. Four isolates were defined as virulent strains, whose virulence was equivalent to the standard strain, ATCC 1961E with a mouse LD50 between 1.2 × 108 CFU/mL and 6.0 × 108 CFU/mL. The LD50 of the screened low virulent strain 09-132 was 1.7 × 1011 CFU/mL . Conclusions: There is a potential risk of Listeria food poisoning in Chongqing City, and the internalized gene (inlA, inlB, inlC, inlJ) loss may lead to virulence declination, while the prfA and plcB genes are less relevant to the virulent isolates.

Key words: Listeria monocytogenes, virulence, gene, PCR