title: Lactic acid resistance of Shiga toxin-producing Escherichia coli and multidrug-resistant and susceptible Salmonella Typhimurium and Salmonella Newport in meat homogenate.
abstract: This study compared lactic acid resistance of individual strains of wild-type and rifampicin-resistant non-O157 Shiga toxin-producing Escherichia coli (STEC) and of susceptible and multidrug-resistant (MDR) and/or MDR with acquired ampC gene (MDR-AmpC) Salmonella against E. coli O157:H7. After inoculation of sterile 10% beef homogenate, lactic acid was added to a target concentration of 5%. Before acid addition (control), after acid addition (within 2 s, i.e. time-0), and 2, 4, 6 and 8 min after addition of acid, aliquots were removed, neutralized, and analyzed for survivors. Of wild-type and of rifampicin-resistant non-O157 STEC strains, irrespective of serogroup, 85.7% (30 out of 35 strains) and 82.9% (29 out of 35 strains), respectively, reached the detection limit within 0-6 min. Of Salmonella strains, 87.9% (29 out of 33 isolates) reached the detection limit within 0-4 min, irrespective of antibiotic resistance phenotype. Analysis of non-log-linear microbial survivor curves indicated that non-O157 STEC serogroups and MDR and susceptible Salmonella strains required less time for 4D-reduction compared to E. coli O157:H7. Overall, for nearly all strains and time intervals, individual strains of wild-type and rifampicin-resistant non-O157 STEC and Salmonella were less (P < 0.05) acid tolerant than E. coli O157:H7.
authors.affiliation: Center for Meat Safety & Quality, Department of Animal Sciences, Colorado State University, Fort Collins, CO 80523-1171, USA.
authors.forename: Aliyar
authors.initials: A
authors.lastname: Fouladkhah
authors.forename: Ifigenia
authors.initials: I
authors.lastname: Geornaras
authors.forename: Hua
authors.initials: H
authors.lastname: Yang
authors.forename: John N
authors.initials: JN
authors.lastname: Sofos
mesh_terms: D000818:Animals; D002417:Cattle; D024901:Drug Resistance, Multiple, Bacterial; D005519:Food Preservation; D005520:Food Preservatives / Q000494:pharmacology*; D019344:Lactic Acid / Q000494:pharmacology*; D008461:Meat Products / Q000032:analysis / Q000382:microbiology*; D050296:Microbial Viability / Q000187:drug effects; D012475:Salmonella / Q000187:drug effects* / Q000254:growth & development; D012486:Salmonella typhimurium / Q000187:drug effects* / Q000254:growth & development; D054323:Shiga-Toxigenic Escherichia coli / Q000187:drug effects* / Q000254:growth & development
chemical_list: D005520:Food Preservatives; D019344:Lactic Acid
keywords: Lactic acid; Multidrug-resistant Salmonella; Shiga toxin-producing Escherichia coli