Lateral flagella are required for increased cell adherence, invasion and biofilm formation by Aeromonas spp.

Two types of flagella are responsible for motility in mesophilic Aeromonas strains. A polar unsheathed flagellum is expressed constitutively that allows the bacterium to swim in liquid environments and, in media where the polar flagellum is unable to propel the cell, Aeromonas express peritrichous lateral flagella. Recently, Southern blot analysis using a DNA probe based on the Aeromonas caviae Sch3N lateral flagellin gene sequence showed a good correlation between strains positive for the DNA probe, swarming motility and the presence of lateral flagella by microscopy. Here, we conclude that the easiest method for the detection of the lateral flagellin gene(s) is by PCR (polymerase chain reaction); this showed good correlation with swarming motility and the presence of lateral flagella. This was despite the high degree of DNA heterogeneity found in Aeromonas gene sequences. Furthermore, by reintroducing the laf (lateral flagella) genes into several mesophilic lateral-flagella-negative Aeromonas wild-type strains, we demonstrate that this surface structure enhances the adhesion to and invasion of HEp-2 cells and the capacity for biofilm formation in vitro. These results, together with previous data obtained using Laf- mutants, demonstrate that lateral flagella production is a pathogenic feature due to its enhancement of the interaction with eukaryotic cell surfaces.