Resistance of biofilm- and pellicle-embedded strains of Escherichia coli encoding the transmissible locus of stress tolerance (tLST) to oxidative sanitation chemicals

Biofilm formation in food processing plants reduces the efficacy of sanitation. The presence of transmissible locus of stress tolerance (tLST) also enhances resistance of planktonic cells of Escherichia coli to sanitation chemicals but the role of tLST in resistance of biofilm-embedded cells remains unclear. This study investigated the link of tLST to biofilm formation and its contribution to resistance of biofilm-embedded E. coli to sanitation. Biofilms were formed as single-strain and as dual-strain biofilms in association with E. coli, Aeromonas australensis or Carnobacterium maltaromaticum. Biofilms on stainless steel were compared to floating biofilms formed at the air-liquid interface (pellicles). The resistance of biofilm-embedded tLST positive strains of E. coli to chlorine, hydrogen peroxide, and peroxyacetic acid was higher than the resistance of tLST negative strains. Higher biofilm density as measured by crystal violet staining was observed in tLST-positive strains of E. coli when compared to tLST negative strains. Biofilm density positively correlated to resistance to disinfectants. The use of confocal laser scanning microscopy detected more compact structure of pellicles compared to solid surface-attached biofilms, resulting in higher chlorine resistance despite the absence of tLST in strains of E. coli. Collectively, the findings of this study elucidated the impact of tLST in strains of E. coli on biofilm formation and sanitizer resistance. These findings may inform the development of improved sanitization protocols for food facilities.