Survival of Salmonella strains Differing in Their Biofilm-Formation Capability upon Exposure to Hydrochloric and Acetic Acid and to High Salt

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Acidic and osmotic treatments are part of hurdle systems to control pathogens such as Salmonella in food. In the current study, Salmonella enterica isolates previously shown to differ in their ability to form biofilms were grown in diluted tryptic soy broth (TSB) (1:5 dilution in distilled water) and subsequently exposed to phosphate-buffered saline (PBS) adjusted to pH 3.0 with HCl, PBS adjusted to pH 3.9 with acetic acid, or rice vinegar diluted 1:15 with distilled water (pH 3.9). Cells grown in diluted TSB were also exposed to PBS, pH 7.6, containing 5 M NaCl. No differences in survival upon exposure to PBS adjusted to pH 3.0 with HCl or containing high salt were observed between the isolates; however, exposure to acetic acid resulted in lower survival levels of isolates previously shown to be poor biofilm formers. The number (log10 cfu/ml) of surviving cells after 36 hr exposure to acetic acid and rice vinegar were 4.43 ± 0.24 vs. 2.27 ± 0.87 (P<0.05), and 5.19 ± 0.12 vs. 2.33 ± 0.93 (P<0.05) for isolates with a high vs. low biofilm-forming ability. The survival data could be fitted with the Weibull model. The data suggest that the ability of Salmonella strains to survive in the presence of acetic acid and rice vinegar parallels their ability to form biofilms. Thus Salmonella with a high biofilm-formation capability might be more difficult to kill with acetic acid found in foods or cleaning solutions.