AUTHOR=Chen Hong-Xian , Chen Fang-Jie , Zhou Qian-Jin , Shang Shi-Lin , Tang Biao , Xu Zhong-Jie , Duan Li-Jun , Jin Jing-Lei , Xu Gui-Zong , Yan Mao-Cang , Chen Jiong 

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

JOURNAL=Frontiers in Microbiology

VOLUME=15

YEAR=2024

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2024.1401802

DOI=10.3389/fmicb.2024.1401802

ISSN=1664-302X

ABSTRACT=<sec><title>Introduction</title><p><italic>Aeromonas</italic> spp. are ubiquitous inhabitants of ecosystems, and many species are opportunistically pathogenic to humans and animals. Multidrug-resistant (MDR) <italic>Aeromonas</italic> species have been widely detected in hospitals, urban rivers, livestock, and aquatic animals.</p></sec><sec><title>Results</title><p>In this study, we identified two <italic>Aeromonas</italic> isolates, namely <italic>Aeromonas veronii</italic> 0728Q8Av and <italic>Aeromonas caviae</italic> 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 <italic>Aeromonas</italic> isolates. Furthermore, a chromosomal <italic>mcr-3.16</italic> gene was identified in <italic>A. veronii</italic> 0728Q8Av, while a chromosomal <italic>mcr-3.3</italic> was found in <italic>A. caviae</italic> 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 <italic>mcr-3-like</italic> was found adjacent to <italic>mcr-3.16</italic> to form a tandem <italic>mcr-3.16</italic>-<italic>mcr-3-like</italic>-<italic>dgkA</italic> structure; yet, <italic>Escherichia coli</italic> carrying the recombinants of <italic>mcr-3-like</italic> did not exhibit resistance to colistin. And an incomplete <italic>mcr-3-like</italic> was found adjacent to <italic>mcr-3.3</italic> in <italic>A. caviae</italic> 1029Y16Ac, suggesting the possibility that <italic>mcr-3</italic> variants originated from <italic>Aeromonas</italic> species. <italic>In vivo</italic> bacterial pathogenicity test indicated that <italic>A. veronii</italic> 0728Q8Av exhibited moderate pathogenicity towards infected ayu, while <italic>A. caviae</italic> 1029Y16Ac was non-virulent.</p></sec><sec><title>Discussion</title><p>Thus, both <italic>Aeromonas</italic> species deserve further attention regarding their antimicrobial resistance and pathogenicity.</p></sec>