Abstract

Escherichia coli (E. coli) is a major pathogen responsible for mastitis and calf diarrhea in dairy cows and has developed heteroresistance (HR) to a wide range of antibiotics. An increasing number of animal studies have shown that the presence of heteroresistance leads to failure of antibiotic therapy. The aims of this study were to investigate whether heteroresistance exists in E. coli and to investigate the biological characteristics of heteroresistant E. coli and its resistant subpopulations in order to investigate possible heteroresistance mechanisms. In this study, we screened heteroresistant E. coli by the Minimum Inhibitory Concentration (MIC) test, Kirby–Bauer (K-B) test, and population analysis profile (PAP), and analyzed the heteroresistance bacteria by a combination of resistance stability test, growth curve test, biofilm formation ability test, transcriptomics and qRT-PCR characterization and mechanism. The results of the K-B test, MIC test and PAP experiments showed that the strains D2, D8, D14, D15, and D19 were heteroresistant to amoxicillin/clavulanic acid (AMC), and the frequency of heteroresistant subpopulations ranged from 3.95 × 10−6 to 8.11 × 10−5. The resistant subpopulation resistance of strain D2 was stable and there was no growth lag. The results of transcriptomics testing confirmed that the heteroresistance mechanism involves ompF, reduced or absent ompC pore protein expression, and increased biofilm formation. This finding provides new insights into the molecular regulatory pathways involved in the development of heteroresistant strains of E. coli.

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