Biofilm Formation of O157 and Non-O157 Shiga Toxin-Producing Escherichia coli and Multidrug-Resistant and Susceptible Salmonella Typhimurium and Newport and Their Inactivation by Sanitizers

This study compared biofilm formation by 7 serogroups of pathogenic Escherichia coli and 2 or 3 phenotypes of Salmonella (susceptible, multidrug-resistant [MDR], and/or multidrug resistant with ampC gene [MDR-AmpC]). One-week mature biofilms were also exposed to water, quaternary ammonium compound-based (QAC), and acid-based (AB) sanitizers. Seven groups (strain mixture) of above-mentioned pathogens were separately spot-inoculated onto stainless steel coupons surfaces for target inoculation of 2 log CFU/cm(2), then stored statically, partially submerged in 10% nonsterilized meat homogenate at 4, 15, and 25 degrees C. Biofilm cells were enumerated on days 0, 1, 4, and 7 following submersion in 30 mL for 1 min in water, QAC, and AB. Counts on inoculation day ranged from 1.6 +/- 0.4 to 2.4 +/- 0.6 log CFU/cm(2) and changed to 1.2 +/- 0.8 to 1.9 +/- 0.8 on day 7 at 4 degrees C with no appreciable difference among the 7 pathogen groups. After treatment with QAC and AB on day 7, counts were reduced (P < 0.05) to less than 0.7 +/- 0.6 and 1.2 +/- 0.5, respectively, with similar trends among pathogens. Biofilm formation at higher temperatures was more enhanced; E. coli O157:H7, as an example, increased (P < 0.05) from 1.4 +/- 0.6 and 2.0 +/- 0.3 on day 0 to 4.8 +/- 0.6 and 6.5 +/- 0.2 on day 7 at 15 and 25 degrees C, respectively. As compared to 4 degrees C, after sanitation, more survivors were observed for 15 and 25 degrees C treatments with no appreciable differences among pathogens. Overall, we observed similar patterns of growth and susceptibility to QAC and AB sanitizers of the 7 tested pathogen groups with enhanced biofilm formation capability and higher numbers of treatment survivors at higher temperatures.