Purpose: The efficacy of lactic acid (LA) decontamination of beef trimmings was evaluated against (i) six non-O157 Shiga toxin-producing E. coli (nSTEC) serotypes, and (ii) antibiotic susceptible and multidrug resistant S. Newport and S. Typhimurium. The antimicrobial effects against these pathogens were compared to those obtained against E. coli O157:H7.
Methods: Four-strain mixture inocula of rifampicin-resistant E. coli O157:H7, O26, O45, O103, O111, O121 and O145, and antibiotic susceptible and multidrug resistant (MDR and/or MDR-AmpC) S. Newport and S. Typhimurium were evaluated on beef trimmings (100-g pieces). The inoculated (3 log CFU/cm2) trimmings were immersed (30 s) in solutions of LA (5%, 25 and 55 °C). Pathogen populations on untreated and treated samples were enumerated (two repetitions, three samples each), and data were analyzed as a complete randomized block design.
Results: Initial levels (3.1-3.3 log CFU/cm2) of E. coli O157:H7 and nSTEC serotypes were reduced (P < 0.05) by 0.7 (E. coli O157:H7) and 0.4-0.9 (nSTEC) log CFU/cm2 in 25 °C LA-treated samples, and 1.4 (E. coli O157:H7) and 1.0-1.3 (nSTEC) log CFU/cm2 in 55 °C LA-treated samples. No differences (P ≥ 0.05) were obtained between surviving counts of the six nSTEC serotypes and those of E. coli O157:H7. LA at 25 °C and 55 °C reduced (P < 0.05) Salmonella counts (3.0-3.3 log CFU/cm2) by 1.2-1.5 and 1.5-1.9 log CFU/cm2, respectively, while corresponding E. coli O157:H7 reductions were 0.5 and 1.2 log CFU/cm2, respectively. Reductions of Salmonella counts were not influenced by serovar or antibiotic resistance profile, and were similar (P ≥ 0.05) or higher (P < 0.05) than reductions of E. coli O157:H7.
Significance: The results indicated that LA decontamination of beef trimmings can be as effective against the six nSTEC serotypes and antibiotic susceptible and multidrug resistant S. Newport and S. Typhimurium as it is against E. coli O157:H7.