EXPRESSION OF INTERNALIN A AND BIOFILM FORMATION AMONG LISTERIA MONOCYTOGENES CLINICAL ISOLATES

Internalin A (InIA), a cell wall-bound protein of Listeria monocytogenes, is among the major components involved in the adhesion to and invasion of host cells expressing specific forms of E-cadherin. Some L. monocytogenes strains secrete truncated non-functional forms of InIA. The purpose of this study is to compare the biofilm-forming abilities of L. monocytogenes strains from clinical sources expressing InIA proteins in the different forms. A total of 70 L. monocytogenes strains were examined using SDS-PAGE, Western blot, DNA sequencing, and microtitre plate biofilm formation assays. We found that 8 of the 70 strains expressed truncated InIA, and that this group of strains exhibited significantly enhanced biotilm-forming ability compared to the group expressing full-length InIA. Further experiments showed that: (i) L. monocytogenes biofilms were detached by treatment with protease K; (ii) protein fragments resulting from proteolysis, rather than intact proteins, are responsible for biofilm enhancement, because biofilm formation was impaired by the protease inhibitor alpha 2-macroglobulin; (iii) truncated and/or proteolytically cleaved InIA are likely involved in the biofilm enhancement, based on the effects that anti-InIA monoclonal antibodies produced on the biofilm formation of L. monocytogenes strains expressing either truncated or full-length InIA. These data provide a basis for further investigation of the molecular structure and composition of L. monocytogenes biofilms.