Abstract
Colistin is considered a last-resort reserved drug for the treatment of critical human infections by Gram-negative bacteria. Phenotypic colistin-resistance is strongly associated with plasmid-mediated mobile colistin resistance (mcr) genes. The mcr-bearing Enterobacteriaceae have been detected in many countries from environments, animals, and humans. This study investigated phenotypic colistin-resistance and the distribution of mcr-1, mcr-2, mcr-3, mcr-4, and mcr-5 genes in chicken-gut bacteria in Bangladesh. Bacteria were isolated from poultry- and native-chicken droppings, and their susceptibilities to colistin were determined by agar dilution and E-test minimal inhibitory concentration (MIC) measurements. Multiplex polymerase chain reactions detected mcr-1 to mcr-5 genes. Overall, 61.7% (92/149) of the isolates showed colistin resistance by agar dilution assessment (MIC > 2.0 μg/mL). The phenotypic resistance was observed considerably higher in poultry-chicken isolates (64.6%, 64/99) than in native-chicken isolates (56%, 28/50; p = 0.373). All the resistant isolates showed MIC levels between > 2 and > 128 μg/mL. The mcr-genes (mcr-1and mcr-2 combined) were detected more in poultry gut bacteria (36.4%) than native-chicken isolates (20%, p = 0.06). Despite bacteria sources, mcr-genes appeared to be significantly associated with phenotypic colistin-resistance phenomena (p < 0.001). Prior colistin usage led to a substantial increase in the proportion of bacteria with mcr-genes and phenotypic resistance (p < 0.001).
Highlights
Colistin is considered a last-resort reserved drug for the treatment of critical human infections by Gram-negative bacteria
This study investigated the prevalence of the mcr-1 to mcr-5 genes linked to phenotypic colistin resistance in farm-origin poultry chicken bacteria and householddwelling native chicken isolates in Bangladesh
The managers were familiar with different brand names of ‘over the counter’ (OTC) antimicrobials and growth-promoting drugs used for chickens
Summary
Colistin is considered a last-resort reserved drug for the treatment of critical human infections by Gram-negative bacteria. This study investigated phenotypic colistin-resistance and the distribution of mcr-1, mcr-2, mcr-3, mcr-4, and mcr-5 genes in chickengut bacteria in Bangladesh. Prior colistin usage led to a substantial increase in the proportion of bacteria with mcr-genes and phenotypic resistance (p < 0.001). Multiple studies have reported a strong association of antimicrobial usage (AMU) in animals with the extensive AMR b urden[2,3]. Acquisition of the plasmid-mediated mobilized colistin resistance gene variant-1 (mcr-1) was first described in Enterobacteriaceae from both farm-animal products and humans[7]. This study investigated the prevalence of the mcr-1 to mcr-5 genes linked to phenotypic colistin resistance in farm-origin poultry chicken bacteria and householddwelling native chicken isolates in Bangladesh
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