Purpose: Evaluation of the effect of AHLs produced by Hafnia alvei on the ability of Salmonella Typhimurium to form biofilm on two abiotic substrata.
Methods: S. Typhimurium was left to form biofilm on stainless steel (SS) and polystyrene (PS) surfaces for 12, 24 and 48 h in either the absence, or presence (50% v/v) of cell-free culture supernatant (CFCS) of H. alvei. To do this, the growth media used to support biofilm development were based on tryptic soy broth (TSB), which also contained CFCS of either the AHL-producing Hafnia alvei 718 or the AHL-lacking isogenic mutant. Biofilm formation on SS was evaluated by cell detachment and colony enumeration, while the crystal violet binding assay was used to do the same for the PS surfaces.
Results: Biofilm formation increased as incubation time increased, regardless of the growth medium composition and the surface. The presence of CFCS containing AHLs seemed to reduce the quantity of strongly attached/biofilm cells recovered from SS after 12 h of incubation, compared to pure TSB or TSB containing CFCS of the mutant strain. No such inhibitory effect was observed on the PS surface following the same incubation period. For both surfaces, no further differences on biofilm formed under the different treatments were observed following 24 and 48 h of incubation.
Significance: The present study provides some data on the influence of cell-to-cell communication on biofilm formation by an important foodborne pathogenic bacterium.