Comparison of phenotypic and WGS-derived antimicrobial resistance profiles of enteroaggregative Escherichia coli isolated from cases of diarrhoeal disease in England, 2015-16

Objectives: Phenotypic and genotypic methods for the detection of antimicrobial resistance (AMR) in enteroaggregative Escherichia coli (EAEC) were compared and evaluated. Methods: WGS data from 155 isolates of EAEC isolated between June 2015 and December 2016 were mapped to genes known to be associated with phenotypic AMR. Results: Phenotypic and genotypic testing of 155 isolates against 10 antimicrobial classes resulted in a total of 25 (1.6%) discordant results of a possible 1550 isolate/antimicrobial combinations. Twenty-three of the mismatches were observed in streptomycin or sulphonamide resistance profiles. These discrepancies were associated with either insertions or truncations in the genes predicted to confer resistance, or in their promotors, rendering them non-functional, or with the presence of aadA variants associated with reduced expression. The most common resistances detected were to ampicillin (56.1%), the sulphonamides (49.7%) and trimethoprim (48.4%). The presence of CTX-M ESBL variants and/or acquired AmpC was detected in 87 of 155 (56.1%) isolates and 18 of 155 (11.6%) isolates were resistant to ciprofloxacin. Eighty-eight (56.8%) isolates were MDR. Conclusions: Phenotypic and genome-derived AMR comparisons showed good correlation for EAEC. A better understanding of the role of allelic variants, specific gene combinations and promoter/attenuator mechanisms in the phenotypic manifestation will improve our ability to provide a robust interpretation of the data for surveillance purposes and, ultimately, in the clinical setting.