Assessing biofilm formation by Salmonella enterica serovar Typhimurium on abiotic substrata in the presence of quorum sensing signals produced by Hafnia alvei

- Correlation was observed between biofilm formation on SS and PS surfaces.
- Conductance detection times inversely well correlated to biofilm counts on SS.
- S. Typhimurium produced more biofilm in 10% TSB compared to 100% TSB.
- AHLs produced by H. alvei did not influence biofilm formation by S. Typhimurium.
- Synthetic 3OC6-HSL did not influence biofilm formation by S. Typhimurium.

This study aimed to evaluate the possible impact of N-acyl-homoserine lactones (AHLs) produced by Hafnia alvei on the biofilm-forming ability of Salmonella enterica ser. Typhimurium. To do this, S. Typhimurium was left to form biofilms on two abiotic substrata, stainless steel (SS) and polystyrene (PS), through their static incubation for up to 48 h, at 20 °C, in laboratory growth media, also containing crude or ethyl acetate extracted cell-free culture supernatant of either the AHL-producing H. alvei 718 strain or its AHL-lacking isogenic mutant. Apart from the presence of signals, two nutritional conditions, a rich and a poor one, were also evaluated in those experiments involving the ethyl acetate extracted supernatants. The presence of AHLs in all media was tested using Agrobacterium tumefaciens biosensor-based bioassay, while the quantities of biofilms formed were in parallel estimated through three different quantification methods, namely agar plating, conductance, and absorbance measurements. Results revealed a significant correlation in biofilm formation among both tested surfaces, with the conductance detection times to be also inversely well correlated to the biofilm counts on SS. Interestingly, S. Typhimurium in general presented a higher capability to form biofilms under the nutrient poor compared to rich conditions. However, all hereby employed biofilm setup and quantification methods did not reveal any significant influence of H. alvei AHLs on Salmonella biofilm-forming behavior. In agreement, further experiments conducted using a synthetic AHL (i.e.3OC6-HSL), simulating a major such signal produced by H. alvei, did not show any effect. To sum up, these results expand our knowledge on the potential role of interspecies signaling on biofilm formation by S. Typhimurium.