Efficacy of Chemical Interventions against Escherichia coli O157:H7 and Multidrug-Resistant and Antibiotic-Susceptible Salmonella on Inoculated Beef Trimmings

Studies were conducted to compare the decontamination efficacy of six chemical treatments against Escherichia coli O157:H7 and multidrug-resistant and antibiotic-susceptible Salmonella inoculated on beef trimmings. The inocula, comprising four-strain mixtures of rifampin-resistant E. coli O157:H7 and antibiotic-susceptible or multidrug-resistant (MDR and/or MDR-AmpC) Salmonella Newport and Salmonella Typhimurium, were inoculated (3 log CFU/cm2) separately onto samples (10 by 5 by 1 cm) derived from beef chuck rolls. Samples were left untreated (control), were immersed for 30 s in acidified sodium chlorite (0.1%, pH 2.5), peroxyacetic acid (0.02%, pH 3.8), sodium metasilicate (4%, pH 12.6), Bromitize Plus (0.0225% active bromine, pH 6.6), or AFTEC 3000 (pH 1.2), or were immersed for 5 s in SYNTRx 3300 (pH 1.0). Levels of surviving Salmonella on treated trimmings were not influenced by serotype or antibiotic resistance phenotype and were generally similar (P > 0.05) or lower (P < 0.05) than levels of surviving E. coli O157:H7 regardless of antimicrobial treatment. Overall, depending on chemical treatment (reductions within each chemical treatment were similar among all tested inocula), initial counts of E. coli O157:H7 (2.7 to 3.1 log CFU/cm2) were reduced (P < 0.05) by 0.2 to 1.4 log CFU/cm2. Similarly, initial counts of the tested Salmonella inocula (2.8 to 3.3 log CFU/cm2) were reduced (P < 0.05) by 0.4 to 1.4 (Salmonella Newport, antibiotic susceptible), 0.3 to 1.4 (Salmonella Newport, MDRAmpC), 0.2 to 1.5 (Salmonella Typhimurium, antibiotic susceptible), 0.4 to 1.3 (Salmonella Typhimurium, MDR), and 0.4 to 1.5 (Salmonella Typhimurium, MDR-AmpC) log CFU/cm2, depending on antimicrobial treatment. Reductions obtained with sodium metasilicate were 1.3 to 1.5 log CFU/cm2, regardless of inoculum, and reductions obtained with the five remaining antimicrobial treatments were 0.2 to 0.7 log CFU/cm2 (depending on treatment). Findings of this study should be useful to regulatory authorities and the meat industry as they consider Salmonella contamination on beef trimmings.