Wild-type cutoff for Apramycin against Escherichia coli
Background Apramycin is used exclusively for the treatment of Escherichia coli ( E.coli ) infections in swine around the world since the early 1980s. Recently, many research papers have demonstrated that apramycin has obvious in vitro activity against multidrug-resistant Enterobacteriaceae isolated in hospitals. Therefore, ensuring the proper use of apramycin in veterinary clinics is of great significance of public health. The objectives of this study were to develop a wild-type cutoff for
... ype cutoff for apramycin against E.coli using a statistical method recommended by Clinical and Laboratory Standards Institute (CLSI) and to investigate the prevalence of resistance genes that confer resistance to apramycin in E. coli . Results Antibacterial susceptibility testing of 1230 E.coli clinical isolates from swine were determinded by broth microdilution testing according to the CLSI document M07-A9. A total number of 310 E.coli strains from different minimum inhibitory concentration (MIC) subsets (0.5-256 µg/mL) were conveniently selected for the detection of resistance genes ( aac(3)-IV ; npmA ; apmA ) in E. coli by PCR. The percentage at each MIC (0.5, 1, 2, 4, 8, 16, 32, 64, 128, and 256 µg/mL) was 0.08%, 0.08%, 0.16%, 2.93%, 31.14%, 38.86%, 12.85%, 2.03%, 1.46%, and 10.41%. The MIC 50 and MIC 90 were 16 and 64 µg/mL. All the 310 E.coli isolates were negative for npmA and apmA gene, and only the aac(3)-IV gene was detected in this study. Conclusions The wild-type cutoff for apramycin against E.coli was defined as 32 µg/mL. The prevelance of aac(3)-IV gene mainly concentrated in these MIC subsets 'MIC ≥ 64 µg⁄ mL', which indicates that the wild-type cutoff established in our study is reliable. The wild-type cutoff offers interpretion criteria of apramycin susceptibility testing of E.coli .