Submitted to: Bulletin of Environmental Contamination and Toxicology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/26/2005
Publication Date: 11/20/2005
Citation: Beier, R.C., Bischoff, K.M., Ziprin, R.L., Poole, T.L., Nisbet, D.J. 2005. Chlorhexidine susceptibility, virulence factors, and antibiotic resistance of beta-hemolytic Escherichia coli isolated from neonatal swine with diarrhea. Bulletin of Environmental Contamination and Toxicology. 75:835-844. Interpretive Summary: The emergence of antimicrobial resistance has become a serious problem worldwide to both animal and human health. There has been evidence to link the use of biocides to the development of antibiotic resistance. In this study we evaluated disease-causing Escherichia coli isolated from baby pigs for potential resistance to the chemical chlorhexidine, a disinfectant commonly used in both animal husbandry and human medicine. Forty-four percent of the isolates tested showed reduced-susceptibility to chlorhexidine. The bacteria tested were grouped by a gene analysis process called ribotyping. Those isolates that showed reduced-susceptibility to chlorhexidine were genetically related to each other. These same reduced-susceptible isolates also correlated to certain virulence factors determined by laboratory techniques on each of the isolates. However, it was shown that even though most of these reduced-susceptible isolates were resistant to a number of antibiotics, there was no correlation between the observed disinfectant resistance and any one antibiotic resistance.
Technical Abstract: The emergence of antimicrobial resistance has become a serious problem worldwide to both animal and human health. There is evidence that the use of biocides may contribute to the development of antibiotic resistance; however, information on susceptibility to disinfectants is limited among veterinary bacterial pathogens. In this study eighty-nine beta-hemolytic Escherichia coli isolated from swine were tested for susceptibility to chlorhexidine digluconate using broth microdilution techniques. Data were compared to ribogroup, virulence factor genotypes, and antibiotic resistance phenotypes. Forty-four percent of the isolates showed decreased susceptibility to chlorhexidine (MICs of two, four, and eight times the JM-109 control, with 5.6%, 25.8% and 12.4% of the isolates, respectively). Most (26 of 39) of the chlorhexidine reduced-susceptible isolates clustered in one ribogroup, however, seven of the 19 ribogroups observed for all 89 isolates contained at least one chlorhexidine reduced-susceptible isolate. Decreased susceptibility correlated with four virulence factor genotypes (STA, STB, SLT2 and F107). Most of these isolates were also resistant to six antibiotics, but the isolates did not correlate to any specific antibiotic resistance phenotype. Even though many of the isolates showed resistance to a high number of antibiotics, there appeared to be no correlation to the observed chlorhexidine resistance. Correlation of chlorhexidine resistance to ribogroups and to the presence of virulence factors suggests that the use of disinfectants may select for enterotoxigenic strains of E. coli. Further surveillance is suggested to study potential genetic links between disinfectant resistance and virulence, and to improve the knowledge base of resistance traits, virulence and antibiotic resistance of disinfectants.