Disinfectant and Antibiotic Susceptibility Profiles of Escherichia coli O157:H7 Strains from Cattle Carcasses, Feces, and Hides and Ground Beef from the United States

Abstract

The disinfectant and antibiotic susceptibility profiles of 344 Escherichia coli O157:H7 strains from cattle carcasses, feces, and hides and ground beef from the United States were determined. A low prevalence of antibiotic resistance was observed (14%). The highest prevalences of resistance were to sulfisoxazole (10.5%), tetracycline (9.9%), streptomycin (7%), and chloramphenicol (4.9%). Four strains were resistant to eight antibiotics (two strains from ground beef and one strain each from hide and preevisceration carcass swabs of cull cattle at harvest). Pulsed-field gel electrophoresis analysis of the E. coli O157:H7 strains revealed two major groups (designated 1 and 2) composed of 17 and 20 clusters, respectively. Clusters 1A, 1B, 1C, and 1G.1 were associated with multidrug-resistant strains. There was no observed correlation between disinfectant resistance and antibiotic resistance. Sixty-nine (20%) of the 344 strains were resistant to chlorhexidine or benzalkonium chloride or the MICs of benzyldimethyldodecylammonium chloride were elevated. Inducible resistance was observed at elevated concentrations of antibiotics (1.4%) and disinfectants (6.1%). The highest rate of disinfectant inducible resistance was to OdoBan, quaternary ammonium chlorides, and the surface disinfectants F25, FS512, and MG, which are used in dairies, restaurants, and food processing plants. High MICs (1,024 to 4,096 m g/ml) of acetic, lactic, and citric acids were found. The decreasing order of acid potency based on molar MICs (MICs(molar)) was acetic, citric, and lactic acid. The correlation of the concentration of dissociated organic acids and MICs(molar) strongly suggests that the observed inhibition of E. coli O157:H7 was primarily due to dissociated forms of the acids.

Interactions of Organic Acids with Salmonella Strains from Feedlot Water-Sprinkled Cattle

“…If pH were the primary factor in inhibition of the bacteria, then one would expect the MICs for these same bacteria for all the different acids would be at the same pH value, but that is not the case. The Salmonella strains demonstrated similar behavior against the organic acids as did E. coli O157:H7 [34], non-O157 STECs [37] and P. aeruginosa [35], except the pH values for the E. coli O157:H7 strains were somewhat lower, possibly because O157:H7 strains are known to have multiple acid-resistance systems to protect them from extreme acid stress [42]. After comparing the study here of Salmonella strains to the previous three studies, E. coli O157:H7 [34], the non-O157 STECs [37] and P. aeruginosa [35], we observed a trend beginning to develop.…”

“…The Salmonella strains demonstrated similar behavior against the organic acids as did E. coli O157:H7 [34], non-O157 STECs [37] and P. aeruginosa [35], except the pH values for the E. coli O157:H7 strains were somewhat lower, possibly because O157:H7 strains are known to have multiple acid-resistance systems to protect them from extreme acid stress [42]. After comparing the study here of Salmonella strains to the previous three studies, E. coli O157:H7 [34], the non-O157 STECs [37] and P. aeruginosa [35], we observed a trend beginning to develop. The MIC M s of 100% of the Salmonella strains with acetic acid was at pH 4.9, 98.6% of non-O157 STECs with acetic acid was at pH 4.79 [37] and the MIC M s of 99% of the P. aeruginosa strains with acetic acid was at pH 4.9 [35].…”

“…Since E. coli O157:H7 has glutamateand arginine-dependent acid-resistance systems to protect it from extreme acid stress [42], we see more acid-tolerance in E. coli O157:H7. The MIC M s of 99.3% of the E. coli O157:H7 with acetic acid were somewhat lower at pH 4.29, but citric and lactic acids had a profound effect resulting in the MIC M s of 98.2% of the E. coli O157:H7 strains at pH 3.95 and pH 3.73, respectively [34]. The MIC M s for the major portion of the Salmonella strains here with citric and lactic acids were also observed about 1 pH unit lower at pH 4.1 and pH 4.2.…”

“…MICs were determined as the lowest concentration of a compound that showed no visible growth of the organism [40]. The organic acid susceptibility studies were carried out similarly to earlier studies with other pathogens [34,35,37]. Briefly, 50 µL of each organic acid solution was diluted 1:2 across a 96-well U-bottom Greiner bio-one microplate ((#82050-626, VWR, Houston, TX, USA) through column 11, and column 12 was the positive control.…”

“…But the specific mechanisms by which pH and organic acids inhibit bacteria are not completely understood [33]. We have previously evaluated Escherichia coli O157:H7 strains from cattle carcasses, feces and hides and ground beef [34], Pseudomonas aeruginosa veterinary isolates [35], and the organic acid inhibition was clearly associated with the dissociated acid species. The disintegration of the LPS layer can be caused by a fully dissociable acid [36].…”