Carbapenem-Resistant Bacteria Recovered from Faeces of Dairy Cattle in the High Plains Region of the USA.

Hattie E Webb,Sophie A Granier,Kendra K Nightingale,H Morgan Scott,Guy H Loneragan,Marie Bugarel,Henk C Den Bakker,Feng Gao

doi:10.1371/journal.pone.0147363

Abstract

ObjectiveA study was conducted to recover carbapenem-resistant bacteria from the faeces of dairy cattle and identify the underlying genetic mechanisms associated with reduced phenotypic susceptibility to carbapenems.MethodsOne hundred and fifty-nine faecal samples from dairy cattle were screened for carbapenem-resistant bacteria. Phenotypic screening was conducted on two media containing ertapenem. The isolates from the screening step were characterised via disk diffusion, Modified Hodge, and Carba NP assays. Carbapenem-resistant bacteria and carbapenemase-producing isolates were subjected to Gram staining and biochemical testing to include Gram-negative bacilli. Whole genome sequencing was performed on bacteria that exhibited either a carbapenemase-producing phenotype or were not susceptible to ertapenem and were presumptively Enterobacteriaceae.ResultsOf 323 isolates collected from the screening media, 28 were selected for WGS; 21 of which were based on a carbapenemase-producing phenotype and 7 were presumptively Enterobacteriaceae and not susceptible to ertapenem. Based on analysis of WGS data, isolates included: 3 Escherichia coli harbouring blaCMY-2 and truncated ompF genes; 8 Aeromonas harbouring blacphA-like genes; 1 Acinetobacter baumannii harbouring a novel blaOXA gene (blaOXA-497); and 6 Pseudomonas with conserved domains of various carbapenemase-producing genes.ConclusionsCarbapenem resistant bacteria appear to be rare in cattle. Nonetheless, carbapenem-resistant bacteria were detected across various genera and were found to harbour a variety of mechanisms conferring reduced susceptibility. The development and dissemination of carbapenem-resistant bacteria in livestock would have grave implications for therapeutic treatment options in human medicine; thus, continued monitoring of carbapenem susceptibility among enteric bacteria of livestock is warranted.

Highlights

Carbapenems have become increasingly important as infections caused by pathogenic bacteria resistant to practically all alternative antibiotics have become globally disseminated throughout the past two decades [1, 2]
Of 323 isolates collected from the screening media, 28 were selected for WGS; 21 of which were based on a carbapenemase-producing phenotype and 7 were presumptively Enterobacteriaceae and not susceptible to ertapenem
Based on analysis of WGS data, isolates included: 3 Escherichia coli harbouring blaCMY-2 and truncated ompF genes; 8 Aeromonas harbouring blacphA-like genes; 1 Acinetobacter baumannii harbouring a novel blaOXA gene; and 6 Pseudomonas with conserved domains of various carbapenemase-producing genes

Summary

Introduction

Carbapenems have become increasingly important as infections caused by pathogenic bacteria resistant to practically all alternative antibiotics have become globally disseminated throughout the past two decades [1, 2]. It is for this reason that carbapenems are reserved as the last resort treatment of multi-drug resistant (MDR) infections in humans. The spread of carbapenem-hydrolysing enzymes among Enterobacteriaceae in hospital settings is of grave concern [3,4,5]. It is likely that the emergence and dissemination of carbapenem-resistant Enterobacteriaceae (CRE) is the consequence of increased reliance on carbapenems for treatment of MDR infections. Carbapenem resistance has become an urgent public health concern largely because CRE are commonly co- or cross- resistant to all other clinically relevant antimicrobials; this, in turn, drastically limits—or eliminates—alternative therapeutic options [6, 7]

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