Pseudomonas aeruginosa is an environmentally ubiquitous and important opportunistic human pathogen responsible for life-threatening health care-associated infections. Because of its extensive repertoire of virulence determinants and intrinsic and acquired resistance mechanisms, the organism could be one of the most clinically and epidemiologically important causes of morbidity and mortality.

The aim of this study was to investigate the presence of colistin-and/or tigecycline-resistant Klebsiella spp. in influents from four wastewater treatment plants (WWTPs) which partly reflect the gut microbiome of human populations. Colistin-and tigecycline-resistant K. pneumoniae isolates (K30/ST29) were detected four times from the WWTP A for three months. Disruptions of the mgrB and ramR genes by ISEc68 and ISKpn21, respectively, were identified in those four isolates. They also shared the IncL/M 86,197-bp plasmids carrying a blaCTX-M-3 and Tn1548-associated armAThose isolates formed a distinct cluster within wgMLST clusters of ST29 K30 public reference strains of human origin, and were unique due to harboring Tn21-like mercury resistance operon transposons in addition to silver, copper, and arsenic resistance determinants. Five K. pneumoniae with different STs and 1 K. quasipneumoniae, exhibiting colistin resistance, were detected in WWTPs B, C and D. For those isolates, disruptions of mgrB by ISEc68 (3 isolates) or ISEcl1 (1 isolate), an insertion of IS2 in the mgrB promoter region (1 isolate), and an inactivation of MgrB by nonsense mutation (1 isolate) were identified.Close monitoring of those mcr-negative colistin-and/or tigecycline-resistant bacteria in wastewater influents is imperative to avoid further limiting of treatment options.

Occurrence of blaNDM-1 in a clinical isolate of Acinetobacter lwoffii in Japan: comparison of blaNDM-1-harboring plasmids between A. lwoffii and A. pittii originated from the hospital sink

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