Transcriptional analysis of genes related to biofilm formation, stress-response, and virulence in Listeria monocytogenes strains grown at different temperatures

The genus Listeria includes eight different species, but only Listeria monocytogenes is associated to human illness. This microorganism is capable of growing in temperatures ranging from 4 °C to 37 °C and forming biofilms on processing sites, which is of great concern in the food industry. In this current work, the transcription of genes related to biofilm formation, stress-response, and virulence in two strains of L. monocytogenes, serotypes 1/2a and 4b, growing at 7 °C and 37 °C, was analyzed by quantitative real time PCR (qPCR). For both serotypes, a temperature of 7 °C significantly increased (P < 0.05) the transcription level of sigB, prfA, luxS, sufS, sufU, ltrC and flaA genes when compared to growth at 37 °C, whereas transcription of the hly gene did not vary significantly at the temperatures tested. Incubation at 7 °C increased the transcriptional level of the actA gene only in L. monocytogenes serotype 1/2a. On the other hand, L. monocytogenes serotype 4b showed significantly increased transcription of the degU gene at 7 °C. Interestingly, expression of the agrA gene, which is involved in adhesion and biofilm formation on abiotic surfaces, was not detected in serotype 4b, and its transcription level was lower at 7 °C in serotype 1/2a. These results demonstrate that the two studied L.monocytogenes serotypes, which are responsible for many human listeriosis cases, have different molecular mechanisms at temperatures of 7 °C and 37 °C.