Attachment strength of Listeria monocytogenes and its internalin-negative mutants

A single cell of Listeria monocytogenes attached on food contact surfaces can be a potential source of cross-contamination in a food-processing plant. To see whether internalin A (InlA) and B (InlB), major surface proteins on L. monocytogenes, play a significant role in the attachment process, wild-type L. monocytogenes EGD (LM_EGD) and its isogenic internalin-negative mutants (LM_EGD Delta inlA, LM_EGD Delta inlB, and LM_EGD Delta inlAB) were used to determine attachment strength on inert glass surface. Western blot analysis using InlA and InlB antibodies confirmed the absence of InlA in LM_EGD Delta inlA, InlB in LM_EGD Delta inlB, and both InlA and InlB in LM_EGD Delta inlAB. Regardless of initial attachment numbers, LM_EGD which expressed both InlA and InlB proteins exhibited the strongest attachment strength while the double mutant (LM_EGD Delta inlAB) exhibited the weakest. The two single mutants (LM_EGD Delta inlA and LM_EGD Delta inlB) that expressed only one type of the internalins were shown to have intermediate attachment strength. These results suggest that both InlA and InlB expression play a significant role in the attachment strength of L. monocytogenes on glass surface.