Abstract
BackgroundPlasmid-mediated resistance to the last-resort drugs: carbapenems and colistin is an emerging public health threat. The studies on the prevalence and co-expression of resistant genes among livestock and human pathogens are rare in Nepal. This is the first study in Nepal exploring the prevalence and co-existence of colistin resistance gene, mcr-1 along with carbapenemase resistance gene, OXA-48 in Escherichia coli isolated from poultry and clinical specimens.MethodsA total of 240 rectal swabs from chickens of five different poultry farms of Kathmandu valley and 705 mid-stream urine samples from human subjects attending Kantipur Hospital, Kathmandu were collected between August, 2018 and March, 2019. Rectal swabs and urine specimens were cultured. E. coli isolated from the specimens were screened for antimicrobial susceptibility testing (AST) using disk diffusion method’. Minimum inhibitory concentration (MIC) of colistin was determined by agar dilution method using 0.5 µg/ml to 32 µg/ml. The E. coli isolates were first screened for mcr-1 followed by screening for OXA-48 genes using conventional Polymerase chain reaction (PCR).ResultsOf the total samples analyzed, E. coli was isolated from 31.7% (76/240) of poultry and 7.9% (56/705) of clinical specimens. In AST, 80% (61/76) of E. coli from poultry and 79% (44/56) from clinical specimens were MDR. The phenotypic prevalence of colistin resistance in poultry specimens were 31.6% (24/76) and clinical specimens were 21.4% (12/56). In PCR assay, 27.6% (21/76) of poultry and 19.6% (11/56) of clinical isolates had colistin resistant mcr-1 gene. MICs value of E. coli isolates ranged from 4 to 32 (µg/ml) in both clinical and poultry isolates. Prevalence of co-existing carbapenem resistance gene, OXA-48, among colistin resistant mcr-1 positive isolates was 38% (8/21) in poultry specimens and 18.2% (2/11) in clinical specimens.ConclusionsThe high prevalence of colistin and carbapenem resistant genes, and their co-existence in plasmid DNA of E. coli isolates in this study suggests the possible spread to other animal, human and environmental pathogens. Molecular methods in addition to the conventional diagnostics in laboratories can help in early diagnosis, effective management and control of their potential transmission.
Highlights
Plasmid-mediated resistance to the last-resort drugs: carbapenems and colistin is an emerging public health threat
Two earlier mechanisms: natural and phenotypic mechanisms were suggested among colistin resistant strains, the former occurring via mutations of bacterial genomes while the latter was the result of adaptive mechanism [3]
The main objective of this study was to explore the prevalence and co-existence of colistin resistance gene, mcr-1 along with carbapenemase resistance gene, OXA-48 in Escherichia coli isolated from poultry farms located in Kathmandu, Kavrepalanchok and Bhaktapur and human specimens from patients attending Kantipur Hospital, Tinkune, Kathmandu between August, 2018 and March, 2019
Summary
Plasmid-mediated resistance to the last-resort drugs: carbapenems and colistin is an emerging public health threat. The studies on the prevalence and co-expression of resistant genes among livestock and human pathogens are rare in Nepal. This is the first study in Nepal exploring the prevalence and co-existence of colistin resistance gene, mcr-1 along with carbapenemase resistance gene, OXA-48 in Escherichia coli isolated from poultry and clinical specimens. The plasmid-encoded colistin resistant gene, mcr-1 was first reported in E. coli isolates from livestock and human specimens in China [1]. Until the discovery of mcr-1, all reported polymyxin resistance mechanisms were chromosomally mediated, due to mutation and regulatory changes [2], and had never been reported to occur via horizontal gene transfer [3]. Insertion of mcr-1 into E. coli chromosomes may enable it to become intrinsically resistant, which is expected to become more prevalent in future [8]
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