The variants of polymyxin susceptibility in different species of genus .

The aquatic environment is an important medium for the accumulation and dissemination of antibiotic-resistant bacteria as it is often closely related to human activities. Previous studies paid little attention to the prevalence and mechanism of polymyxin-resistant bacteria in the aquatic environment. As a Gram-negative opportunistic pathogen widely distributed in aquatic ecosystems, the antibiotic-resistant profile of spp. deserves much attention. In this study, we identified 61 spp. isolates from water samples in the section of the Yangtze River. The total polymyxin B (PMB) resistance rate of these strains was 49.18% (30/61), showing a high level of polymyxin resistance in spp. The MIC and MIC for PMB exhibited a significant discrepancy among different species ( < 0.001). The MIC and MIC for PMB in the were 128 mg/L and above 128 mg/L while in and , the MIC and MIC value were both 2 mg/L. Only two . strains (MIC = 2 mg/L) and one . strain (MIC = 0.5 mg/L) were identified as carrying mobilized polymyxin resistant gene ., and .. All genes were located in the chromosome. This is the first report that the downstream region of -3.42 was the truncated -like gene separated by the insertion sequences of IS (1,674 bp) and IS (1,084 bp). Analysis of epidemiology of -positive genomes from GenBank database showed that the genus and the aquatic environment might be the potential container and reservoir of . By the whole-genome sequencing and qRT-PCR, we inferred that the sequence differences in the AAA domain of MlaF protein and its expression level among these three species might be involved in the development of polymyxin resistance. Our study provided evidences of the possible mechanism for the variety of polymyxin susceptibility in different species of the genus and a theoretical basis for the surveillance of the aquatic environment.