Prevalence and genetic analysis of mcr-3-positive Aeromonas species from humans, retail meat, and environmental water samples [PublishAheadOfPrint]

The mobile colistin-resistance gene mcr-3 is globally disseminated in both Enterobacteriaceae and Aeromonas species, the latter of which potentially serves as a reservoir for this gene. Here, we investigated the prevalence of mcr-3 from rectal swabs of humans, food-producing animals and their products, and the aquatic environment, and investigated the genetic relationships between the mcr-3-positive isolates. An enriched broth screening method was used to detect mcr-3 in samples, and species identification of isolates from the positive samples was carried out by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and shotgun sequencing. All mcr-3-positive isolates were subjected to antimicrobial susceptibility testing, conjugation, and whole genome sequencing. Ten Aeromonas isolates, two from human rectal swabs, one from pork, three from chicken meat, and four from the aquatic environment, were positive for mcr-3, but only two showed resistance to colistin. Besides the mcr-3-variants identified before– the novel variants were termed mcr-3.13 to mcr-3.18 – all isolates also harbored mcr-3-like genes downstream of the mcr-3 variants. The MCR-3.13 to MCR-3.18 proteins exhibited only 84–85% amino acid identity to the original MCR-3 protein. Whole genome sequence analysis indicated diversity within the genetic environment of mcr-3-positive Aeromonas isolates, and possible transmission between different sources in China, and even worldwide. Close relationships between mcr-3-positive and -negative Aeromonas isolates suggested that mcr-3 might be common in Aeromonas species, which are not inherent hosts of mcr-3 but may act as an important reservoir of this mobile colistin-resistance gene.

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