Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 3/15/2018
Publication Date: N/A
Technical Abstract: Introduction: Escherichia coli O157:H7 (O157) can cause diarrhea and serious secondary sequelae including kidney failure and death in humans. With antibiotics like fosfomycin, colistin and azithromycin, that do not stimulate toxin expression by O157, being considered for treatment of early gastrointestinal disease it is important to evaluate antibiotic resistance in these E. coli as it could hinder such therapies. Purpose: Cattle are reservoirs of O157 and super-shedding cattle can shed O157 at greater than or equal to 104 CFU/g feces. Taking into account the potential for increased dissemination, we evaluated a genetically diverse set of bovine super shed O157 (SS-O157) isolates for their antibiotic resistance (AR) profiles, and presence of AR genes. Methods: SS-O157 isolates (n equals 53) were tested for sensitivity to 17 antibiotics using the Kirby-Bauer disc diffusion method and screened for the presence of 30 AR genes by PCR and sequencing. Minimum inhibitory concentration (MIC) tests were used to verify resistance (R) and intermediate-resistance (IR) phenotypes. The AR profile of bovine, non-O157 E. coli (n equals 20) and sequenced O157 strains (n equals 7) was similarly analyzed for comparison. Results: A combination of 12 or more resistance genes was identified among the SS-O157 isolates, similar to non-O157 E. coli by PCR and sequencing. While all isolates were sensitive to fosfomycin and colistin, 94 percent SS-O157 and 5 percent non-O157 E. coli demonstrated IR or R phenotypes with azithromycin, respectively. Sulfisoxazole resistance was observed in 83 percent SS-O157 and 40 percent non-O157; isolates also demonstrated resistance to tetracycline, streptomycin, chloramphenicol, nalidixic acid, cefotaxime, cefoxitin, gentamicin, amoxicillin and ampicillin. MIC of these antibiotics is presently being evaluated to verify the results and compare overall data to AR genes characterized by PCR. Significance: SS-O157, like other E. coli, can demonstrate varying antibiotic susceptibility profiles. Resistance to antibiotics could have important clinical implications and hence should be comprehensively verified.