Occurrence of the mcr-1 Colistin Resistance Gene and other Clinically Relevant Antibiotic Resistance Genes in Microbial Populations at Different Municipal Wastewater Treatment Plants in Germany

Abstract

Seven wastewater treatment plants (WWTPs) with different population equivalents and catchment areas were screened for the prevalence of the colistin resistance gene mcr-1 mediating resistance against last resort antibiotic polymyxin E. The abundance of the plasmid-associated mcr-1 gene in total microbial populations during water treatment processes was quantitatively analyzed by qPCR analyses. The presence of the colistin resistance gene was documented for all of the influent wastewater samples of the seven WWTPs. In some cases the mcr-1 resistance gene was also detected in effluent samples of the WWTPs after conventional treatment reaching the aquatic environment. In addition to the occurrence of mcr-1 gene, CTX-M-32, blaTEM, CTX-M, tetM, CMY-2, and ermB genes coding for clinically relevant antibiotic resistances were quantified in higher abundances in all WWTPs effluents. In parallel, the abundances of Acinetobacter baumannii, Klebsiella pneumoniae, and Escherichia coli were quantified via qPCR using specific taxonomic gene markers which were detected in all influent and effluent wastewaters in significant densities. Hence, opportunistic pathogens and clinically relevant antibiotic resistance genes in wastewaters of the analyzed WWTPs bear a risk of dissemination to the aquatic environment. Since many of the antibiotic resistance gene are associated with mobile genetic elements horizontal gene transfer during wastewater treatment can't be excluded.

Genomic epidemiology of multidrug‐resistant Gram‐negative organisms

“…Since its initial observation on an interspecies plasmid in 2015, mcr-1 has been identified in the human gut microbiome, wastewater, community, and animal sources. [123][124][125][126][127] This identification of a previously unknown mobile resistance element in all previously mentioned hypothesized reservoirs demonstrates for mcr-1 what is likely true for other resistance mechanisms: that the transfer and dissemination of mobile resistance is likely due to a complex chain of events that take place across multiple ecological settings. Much of the controversy over which reservoirs are the most important for breeding resistance in healthcare settings stems from the fact that the definitive studies examining relative contributions of hypothesized reservoirs of resistance for prevalent pathogens have yet to be carried out.…”

“…The debate over the relative contributions of different reservoirs to resistance dissemination within hospitals recently came to a head in the case of mcr‐1 , which confers transferrable colistin resistance. Since its initial observation on an inter‐species plasmid in 2015, mcr‐1 has been identified in the human gut microbiome, wastewater, community, and animal sources . This identification of a previously unknown mobile resistance element in all previously mentioned hypothesized reservoirs demonstrates for mcr‐1 what is likely true for other resistance mechanisms: that the transfer and dissemination of mobile resistance is likely due to a complex chain of events that take place across multiple ecological settings.…”

Massive analysis of 64’628 bacterial genomes to decipher a water reservoir and origin of mobile colistin resistance (mcr) gene variants: is there another role for this family of enzymes?

“…E. coli and E. cloacae ) collected from urban surface water, rivers or lakes 37–39 . This gene was reported from wastewater treatment plants in China 40 , in South Africa 41 , in Italia 42 , in Germany 43 or from hospital sewage water in China 44 . This variant was also reported from various bacteria isolated from other water environments, such as seawater in Algeria 45 , from top water in rural China 46 or from freshwater of intensive aquaculture in China 17 .…”

Biological HRPs in wastewater

“…Hrenovic et al (2017) have detected carbapenemresistant bacteria in influent, activated sludge, effluent, digested sludge, and stabilized sludge of the largest Croatian secondary wastewater treatment plant in Zagreb, and found that the number of carbapenem-resistant bacteria in effluent was reduced by more than 99% compared with influent while the relative abundance increased. Hembach et al (2017) have detected mcr-1 gene and some clinical-related genes (including bla CTX-M-32 , bla TEM , bla CTX-M , tet(M), bla CMY-2 , and ermB) in the influent and effluent of seven German WWTPs. Luo et al (2013) have found the NDM-1 gene in disinfected effluent from two STPs in north China with the absolute abundance of 1316 AE 232 and 1431 AE 247 copies/mL, respectively.…”