Two colistin resistance-producing strains, isolated from coastal waters in Zhejiang, China: characteristics, multi-drug resistance and pathogenicity.

Introduction: spp. are ubiquitous inhabitants of ecosystems, and many species are opportunistically pathogenic to humans and animals. Multidrug-resistant (MDR) species have been widely detected in hospitals, urban rivers, livestock, and aquatic animals.

Results: In this study, we identified two isolates, namely 0728Q8Av and 1029Y16Ac, from coastal waters in Zhejiang, China. Both isolates exhibited typical biochemical characteristics and conferred MDR to 11 kinds of antibiotics, remaining susceptible to ceftazidime. Whole-genome sequencing revealed that both isolates harbored multiple antibiotic resistance genes (ARGs) and several mobile genetic elements (MGEs) on the chromosomes, each containing a resistance genomic island (GI), a typical class 1 integron, a transposon, and various insertion sequences (ISs). Most ARGs were situated within the multiple resistance GI, which contained a class 1 integron and a transposon in both isolates. Furthermore, a chromosomal gene was identified in 0728Q8Av, while a chromosomal was found in 1029Y16Ac. Both mcr-3 variants were not located within but were distanced from the multidrug resistance GI on the chromosome, flanking by multiple ISs. In addition, a was found adjacent to to form a tandem -- structure; yet, carrying the recombinants of did not exhibit resistance to colistin. And an incomplete was found adjacent to in 1029Y16Ac, suggesting the possibility that variants originated from species. bacterial pathogenicity test indicated that 0728Q8Av exhibited moderate pathogenicity towards infected ayu, while 1029Y16Ac was non-virulent.

Discussion: Thus, both species deserve further attention regarding their antimicrobial resistance and pathogenicity.