Identifying Environmental Allies: Dual-Species Biofilm Formation Enhances E. coli O157:H7 Stress Tolerance and Postsanitization Survival.

Biofilm formation may lead to meat product contamination. It has been shown that via mixed biofilm formation, the environmental microbial communities may enhance E. coli O157:H7 sanitizer tolerance. To understand how interspecies interactions would influence E. coli O157:H7 colonization and stress tolerance, individual environmental bacterial species were isolated from floor drain samples collected at three beef plants with different E. coli O157:H7 prevalence rates. Forty-two bacterial strains spanning 16 genera and 31 species were isolated, including Pseudomonas, Staphylococcus, Enterococcus, Bacillus, Carnobacterium, Niallia, and Priestia, etc. Biofilm-forming ability was highly strain-dependent; seventeen of the forty-two isolates produced significant biofilms. The strong biofilm-producing strains, along with selected weak biofilm-forming strains (n = 10) representing diverse genera and species, were each examined for dual-species biofilm formation with an E. coli O157:H7 strain. Dual-species biofilms were established either through simultaneous coinoculation of both strains or by sequential inoculation, wherein E. coli O157:H7 was introduced onto a solid surface precolonized by one of the environmental isolates. The mixed biofilms were then treated with sanitizers, including a quaternary ammonium compound (QAC) or chlorine, and postsanitization survival of E. coli O157:H7 was measured. The results demonstrated that the E. coli O157:H7 strain was able to colonize and form mixed biofilms with all the tested environmental strains under both experimental conditions. The diverse natural companion strains exerted distinct impacts on E. coli O157:H7 surface colonization and stress tolerance within the dual-species biofilms. Notably, precolonization by five and two strong and weak biofilm forming strains, respectively, significantly enhanced E. coli O157:H7 surface colonization compared to its single-strain biofilm, whereas coculturing with six other strong biofilm formers significantly reduced E. coli O157:H7 colonization. Multiple environmental strains conferred protection to E. coli O157:H7 against QAC and chlorine sanitization, with the protective effect being species-dependent rather than genus-restricted. Given that meat processing facilities harbor a diverse array of environmental bacterial species, the presence of certain strains capable of promoting pathogen colonization and conferring enhanced stress tolerance may contribute to increased pathogen persistence and contamination risk. This study underscores the importance of species-specific microbial interactions in shaping pathogen survival and may have potential applications for leveraging such interactions in biofilm detection, prevention, and control.