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. 2014 Jul;69(7):1785-91.
doi: 10.1093/jac/dku079. Epub 2014 May 5.

Waste water effluent contributes to the dissemination of CTX-M-15 in the natural environment

G C A Amos  1 , P M Hawkey  2 , W H Gaze  1 , E M Wellington  3
Affiliations

Waste water effluent contributes to the dissemination of CTX-M-15 in the natural environment

G C A Amos et al. J Antimicrob Chemother. 2014 Jul.

Abstract

Objectives: Multidrug-resistant Enterobacteriaceae pose a significant threat to public health. We aimed to study the impact of sewage treatment effluent on antibiotic resistance reservoirs in a river.

Methods: River sediment samples were taken from downstream and upstream of a waste water treatment plant (WWTP) in 2009 and 2011. Third-generation cephalosporin (3GC)-resistant Enterobacteriaceae were enumerated. PCR-based techniques were used to elucidate mechanisms of resistance, with a new two-step PCR-based assay developed to investigate bla(CTX-M-15) mobilization. Conjugation experiments and incompatibility replicon typing were used to investigate plasmid ecology.

Results: We report the first examples of bla(CTX-M-15) in UK river sediment; the prevalence of bla(CTX-M-15) was dramatically increased downstream of the WWTP. Ten novel genetic contexts for this gene were identified, carried in pathogens such as Escherichia coli ST131 as well as indigenous aquatic bacteria such as Aeromonas media. The bla(CTX-M-15) -gene was readily transferable to other Gram-negative bacteria. We also report the first finding of an imipenem-resistant E. coli in a UK river.

Conclusions: The high diversity and host range of novel genetic contexts proves that evolution of novel combinations of resistance genes is occurring at high frequency and has to date been significantly underestimated. We have identified a worrying reservoir of highly resistant enteric bacteria in the environment that poses a threat to human and animal health.

Keywords: CTX-M; antibiotic resistance; carbapenem resistance; environmental pathogens; β-lactamases.

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Figures

Figure 1.
Figure 1.
Counts of 3GC-resistant presumptive E. coli and PCEs from samples collected downstream and upstream of a WWTP in 2009 and 2011. Error bars are ± standard errors of biological replicates.
Figure 2.
Figure 2.
Flanking regions of blaCTX-M-15 recovered in isolates obtained during this study as confirmed by two-step PCR and sequencing. Nomenclature is an extension of a previously defined typing system.
Figure 3.
Figure 3.
Prevalence of different plasmid replicon types as validated by PCR for 41 blaCTX-M-15-bearing isolates from river sediment downstream of WWTP effluent and upstream of WWTP effluent in 2011.
See this image and copyright information in PMC

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