Environmental and Pathogenic Carbapenem Resistant Bacteria Isolated from a Wastewater Treatment Plant Harbour Distinct Antibiotic Resistance Mechanisms.

Micaela Oliveira,Inês Leonardo,Mónica Nunes,Ana Silva,Maria Barreto Crespo

doi:10.3390/antibiotics10091118

Abstract

Wastewater treatment plants are important reservoirs and sources for the dissemination of antibiotic resistance into the environment. Here, two different groups of carbapenem resistant bacteria—the potentially environmental and the potentially pathogenic—were isolated from both the wastewater influent and discharged effluent of a full-scale wastewater treatment plant and characterized by whole genome sequencing and antibiotic susceptibility testing. Among the potentially environmental isolates, there was no detection of any acquired antibiotic resistance genes, which supports the idea that their resistance mechanisms are mainly intrinsic. On the contrary, the potentially pathogenic isolates presented a broad diversity of acquired antibiotic resistance genes towards different antibiotic classes, especially β-lactams, aminoglycosides, and fluoroquinolones. All these bacteria showed multiple β-lactamase-encoding genes, some with carbapenemase activity, such as the blaKPC-type genes found in the Enterobacteriaceae isolates. The antibiotic susceptibility testing assays performed on these isolates also revealed that all had a multi-resistance phenotype, which indicates that the acquired resistance is their major antibiotic resistance mechanism. In conclusion, the two bacterial groups have distinct resistance mechanisms, which suggest that the antibiotic resistance in the environment can be a more complex problematic than that generally assumed.

Highlights

The increasing dissemination of carbapenem resistant bacteria represents a major worldwide problem and an important threat to human health [1]
Environmental and potentially pathogenic carbapenem resistant bacteria were detected at high concentrations in wastewater influent and discharged effluent samples (Supplementary Table S1)
And despite the possible bias induced by this methodology, in which pathogenic carbapenem resistant bacteria are able to grow in the environmental carbapenem resistant bacteria plates, at 30 ◦ C, most of the identified bacteria were described as having an environmental origin, three potentially pathogenic bacteria for both humans and animals were isolated

Summary

Introduction

The increasing dissemination of carbapenem resistant bacteria represents a major worldwide problem and an important threat to human health [1]. In terms of clinical relevance and global distribution, the most important carbapenemases are: (1) Class A serine β-lactamases, encoded by blaKPC -type genes; (2) Class B metallo-βlactamases, encoded by blaNDM , blaIMP , and blaVIM -type genes; and (3) Class D serine-βlactamases, encoded by blaOXA-48 -type genes [5,8] These carbapenemase-encoding genes can be found in the bacterial chromosome, but more often in conjugative plasmids, which promotes their horizontal transfer between resistant and non-resistant bacteria. Bacteria can be resistant to carbapenems due to mutations causing loss of expression of porin-encoding genes; as a result of the overexpression of genes encoding for efflux pumps; or due to mutations that modify the production levels or the binding affinities of the penicillin-binding proteins [1,5] These non-enzyme mediated resistance mechanisms, known as intrinsic resistance mechanisms, can occur alone or together with the production of extended-spectrum β-lactamases, cephalosporinases, and/or carbapenemases, generating well-known carbapenem resistance phenotypes [1,5]

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