Variability in biofilm formation dynamics by Salmonella enterica isolated from animal-origin foods, plant-based foods, environment, clinical, and unspecified food sources: a 3-day in vitro study in tryptic soy broth at ambient temperature.

Abstract

Bacterial biofilm production is linked to its adaptive capacity to environments throughout its lifecycle. This study aimed to assess the variability in biofilm formation (BF) dynamic by Salmonella enterica and to explore the potential impact of the cell's prior history, primarily shaped by strain and its isolation source. In vitro BF of 141 S. enterica strains isolated from animal-origin foods, plant-based foods, unspecified food sources, the environment, and clinical cases, was evaluated using the crystal violet assay at 25 °C for up to 72 h. Kruskal-Wallis test was used to assess the effect of time, source, and strain. The Aryani method was used to characterize microbial response variability. The BF capacity of S. enterica strains ranged from 0.07 to 2.3, 0.07 to 2.7, and 0.06 to 2.7OD_595nm at 24, 48, and 72 h, respectively. At 24 h (66.0%; 93/141) and 48 h (56.0%; 79/141), most isolates were classified as nonbiofilm producers, while at 72 h, the majority were weak biofilm producers (39.7%; 56/141). Time, strain, and isolation source significantly influenced BF, with an overall increase in BF occurring over time, and clinical strains being the highest biofilm producers. Strain to strain variability was the highest contributor to the total variance ( ${\sigma }_{24h}^2$ = 0.18OD_595nm ², ${\sigma }_{48h}^2$ = 0.23OD_595nm ², ${\sigma }_{72h}^2$ = 0.26OD_595nm ²). Analysis of variability between and within isolation source groups revealed the highest variability among clinical isolates ( ${\sigma }_{24h}^2$ = 1.08OD_595nm ², ${\sigma }_{48h}^2$ = 1.36OD_595nm ², ${\sigma }_{72h}^2$ = 1.38OD_595nm ²). Although BF was statistically associated with the strain and its isolation source, the high variability observed within these factors suggests that they alone are insufficient to explain how the cell's prior history influences BF. A more comprehensive undertanding on BF will require considering additional intrinsic and extrinsic factors.