First reported detection of the mobile colistin resistance genes,mcr-8 andmcr-9, in the Irish environment

Abstract

The emergence and dissemination of mobile colistin resistance (mcr) genes across the globe poses a significant threat to public health, as colistin remains one of the last line treatment options for multi-drug resistant infections. Environmental samples (157 water and 157 wastewater) were collected in Ireland between 2018 and 2020. Samples collected were assessed for the presence of antimicrobial resistant bacteria using Brilliance ESBL, Brilliance CRE, mSuperCARBA and McConkey agar containing a ciprofloxacin disc. All water and integrated constructed wetland influent and effluent samples were filtered and enriched in buffered peptone water prior to culture, while wastewater samples were cultured directly. Isolates collected were identified via MALDI-TOF, were tested for susceptibility to 16 antimicrobials, including colistin, and subsequently underwent whole genome sequencing. Overall, eightmcrpositive Enterobacterales (onemcr-8 and sevenmcr-9) were recovered from six samples (freshwater (n=2), healthcare facility wastewater (n=2), wastewater treatment plant influent (n=1) and integrated constructed wetland influent (piggery farm waste) (n=1)). While themcr-8 positiveK. pneumoniaedisplayed resistance to colistin, all sevenmcr-9 harbouring Enterobacterales remained susceptible. All isolates demonstrated multi-drug resistance and through whole genome sequencing analysis, were found to harbour a wide variety of antimicrobial resistance genes i.e., 30 ± 4.1 (10-61), including the carbapenemases,blaOXA-48 (n=2) andblaNDM-1 (n=1), which were harboured by three of the isolates. Themcrgenes were located on IncHI2, IncFIIK and IncI1-like plasmids. The findings of this study highlight potential sources and reservoirs ofmcrgenes in the environment and illustrate the need for further research to gain a better understanding of the role the environment plays in the persistence and dissemination of antimicrobial resistance.

Seasonal Patterns in Mobile Colistin Resistance Gene Variants in Wastewater Bioaerosols and Liquid Sludge

“…15,54−56 Interestingly, while mcr-8 was the second most abundant variant in this study, it has not previously been identified in municipal wastewater and is most often associated with aquatic environments. 15,57,58 The mcr-10 variant was detected only in air samples collected during the spring and summer seasons and was not detected in any WWTP liquid samples. Likewise, mcr-3 was observed in air samples from each WWTP and in liquid samples from WWTP 1 during the fall season.…”

“…However, even with this limitation, the results of this study support previous findings that observed a range of mcr variants in hospital and municipal wastewater. 15,[54][55][56][57]59,60 Additionally, this study is one of the first to examine seasonal patterns of mcr abundance and expands the understanding of environmental routes of mcr dissemination with the identification of mcr variants in WWTP bioaerosols.…”

“…In liquid samples, mcr-8 containing contigs were site specific and associated with Stenotrophomonas, Acinetobacter, Ramlibacter, Azospiro, and an unclassified Burkholderiaceae. While K. pneumoniae is the most commonly identified mcr-8 host, 53,57 it has also been identified in a Stenotrophomonas strain isolated from poultry farm sewage. 71 The mcr-9 variant was identified only in air collected at WWTP 2 and was associated with Salmonella enterica.…”