Alternative sigma factor σB is not essential for Listeria monocytogenes surface attachment

Abstract

Listeria monocytogenes is a foodborne pathogen frequently isolated from the food processing environment. Multiple lines of evidence suggested a possible role for the L. monocytogenes alternative transcription factor sigma B (σB) in surface attachment and biofilm formation. Therefore, through plate count and microscopic techniques, the L. monocytogenes 10403S strain and an otherwise isogenic ΔsigB strain were tested for attachment to stainless steel. Analysis of microscopic images revealed that after 72 h at 24°C under static conditions the tested L. monocytogenes strains attached uniformly to surfaces as single cells. Both strains were capable of rapid attachment (i.e., numbers of attached cells were essentially the same after either 5 min or 24 h of incubation). Numbers of attached ΔsigB cells were significantly lower than those of the wild-type strain after 48 and 72 h of incubation at 24°C (P = 0.001). Similar numbers of the ΔsigB strain attached to stainless steel regardless of temperature (24 or 37°C); however, ΔsigB cells attached at higher relative numbers in the presence of 6% NaCl after 48 and 72 h. Furthermore, in the presence of Pseudomonas fluorescens, similarly high numbers of wild-type and ΔsigB cells attached to the surfaces, forming mixed biofilms. Our data suggest that σB is not required for initial surface attachment of L. monocytogenes.