Typhimurium more greatly affected than E. However, the degree of biofilm formation for both pathogens was substantially reduced in the presence of the competing microbiota, with S. coli O157:H7 can integrate into biofilms when cocultured with bacteria from meat plant processing surfaces. IMPORTANCE Results of this study demonstrate that Salmonella enterica serovar Typhimurium and E. Citrobacter, Hafnia, Aeromonas, and Carnobacterium predominated in biofilms but not always in the planktonic cultures. The relative proportions of facultative anaerobes in both multispecies cultures were greater in both suspensions and biofilms than in the inoculum. Respective fractions of ST and O157 were 2.1% and 0.97% initially and then 0.10% and 0.07% on day 2, and 0.60% and 0.04% on day 6. The changes in the relative abundance of MPB were similar for the two MPB-pathogen cocultures, though different interbacterial interactions were noted. Bacterial diversity in multispecies cultures decreased with incubation time, irrespective of the pathogen or culture type. No difference ( P > 0.05) in bacterial counts was noted for the two MPB-pathogen cocultures at any time during incubation. A similar trend, though to a lesser extent, was observed for O157 in biofilms on day 2 but not on day 6. ST was 3 log higher in single-species than in multispecies biofilms. In suspensions, levels of O157 and ST were ∼2 log higher in single-species than in multispecies cultures on both sampling days. The composition of multispecies cultures was determined by 16S rRNA gene sequencing. Bacteria in suspensions (inoculum, days 2 and 6) and biofilms (days 2 and 6) were enumerated by plating. Biofilms of O157 or ST with/without MPB were developed on stainless steel coupons at 15☌ for up to 6 days. This study investigated the microbial dynamics in multispecies biofilms of Escherichia coli O157:H7 strain 1934 (O157) or Salmonella enterica serovar Typhimurium ATCC 14028 (ST) and 40 strains of meat processing surface bacteria (MPB).
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