Abstract
Simple SummaryThe poultry industry is one of the top agribusinesses in Nepal. However, despite the government’s restriction on the use of antibiotics as growth promotors in animals, the overuse and misuse of antibiotics can be seen all over the country. Such inappropriate use of antibiotics has led to the rise of antibiotic resistance among treatment options for both human and animal pathogens. Several findings suggest the failure of colistin, a polymyxin E antibiotic (once regarded as the last resort drug), in the treatment of human bacterial infections is due to the emergence and spread of the plasmid-mediated colistin resistance gene (mcr-1) among Gram-negative bacterial pathogens. The emergence and rapid transfer of resistant strains in poultry farms are associated with unwanted loss of livestock, economic burden and spread of drug-resistance to other animals, humans and the environment, as well. In this study, we characterized the mcr-1 gene from infected chicken livers, where prevalence was found to be alarmingly high. This study identifies the result of regulatory failures. Therefore, this report provides valuable reference to the policy makers so that a more effective policy can be formulated and implemented to curb the spread of drug-resistant pathogens.Background: Plasmid-mediated resistance to the colistin in poultry is considered as an emerging problem worldwide. While poultry constitutes the major industry in Nepal, there is a paucity of evidence on colistin resistance in Escherichia coli isolates causing natural infections in poultry. This study aimed to explore the prevalence of plasmid-mediated colistin resistance gene, mcr-1 in E. coli isolated from liver samples of dead poultry suspected of E. coli infections. Methods: A total of two hundred and seventy liver samples (227 broilers and 43 layers) from dead poultry suspected of colibacillosis were collected from post-mortem in the Central Veterinary Laboratory (CVL), Kathmandu, between 1 February and 31 July 2019. The specimens were processed to isolate and identify E. coli; an antimicrobial susceptibility test (AST) using disk diffusion method was performed with 12 different antibiotics: Amikacin (30 µg), ampicillin (10 µg), ciprofloxacin (5 µg), chloramphenicol (30 µg), cefoxitin (30 µg), ceftazidime (30 µg), ceftriaxone (30 µg), cotrimoxazole (25 µg), gentamicin (10 µg), imipenem (10 µg), levofloxacin (5 µg) and tetracycline (30 µg). Colistin resistance was determined by agar dilution method and colistin-resistant strains were further screened for plasmid-mediated mcr-1 gene, using conventional polymerase chain reaction (PCR). Results: Out of 270 liver samples, 53.3% (144/270) showed growth of E. coli. The highest number (54%; 109/202) of E. coli isolates was obtained in the liver samples from poultry birds (of both types) aged less than forty days. In AST, 95.1% (137/144) and 82.6% (119/144) of E. coli isolates were resistant against tetracycline and ciprofloxacin, respectively, while 13.2% (19/144) and 25.7% (37/144) isolates were resistant to cefoxitin and imipenem, respectively. In the same assay, 76.4% (110/144) E. coli isolates were multi-drug resistant (MDR). The phenotypic prevalence of colistin resistance was 28.5% (41/144). In the PCR assay, 43.9% (18/41) of colistin-resistant isolates were screened positive for plasmid-mediated mcr-1. Conclusion: The high prevalence of mcr-1 in colistin-resistant E. coli isolates in our study is a cause of concern for the probable coming emergence of colistin resistance in human pathogens, due to horizontal transfer of resistant genes from poultry to human isolates.
Highlights
Escherichia coli is a member of Enterobacteriaceae family of Gram-negative bacteria and a normal inhabitant of the intestinal tract of humans and animals, gut commensals can cause a variety of infections as opportunistic pathogens under favourable conditions [1]
Infections caused by pathogenic E. coli (APEC) in poultry are known as colibacillosis and are responsible for sacculitis, pericarditis, peritonitis, salpingitis, synovitis, osteomyelitis, cellulitis, coligranuloma and yolk sac infections in chicken [2]
A total of 270 liver samples (227 from broiler and 43 from layers), each obtained from individual dead birds that had died with suspected colibacillosis, were obtained from the postmortem department of the Central Veterinary Laboratory (CVL), Kathmandu
Summary
Escherichia coli is a member of Enterobacteriaceae family of Gram-negative bacteria and a normal inhabitant of the intestinal tract of humans and animals, gut commensals can cause a variety of infections as opportunistic pathogens under favourable conditions [1]. Some previous studies based on molecular characterization have confirmed the genetic similarity between E. coli strains (not APEC) isolated from poultry and those isolated from human infections [3]. The burgeoning of antimicrobial resistance (AMR) has compelled the veterinarians to prescribe the drugs which otherwise are not considered as standard regimen of therapy. One such instance is colistin, a polymyxin. Plasmid-mediated resistance to the colistin in poultry is considered as an emerging problem worldwide. This study aimed to explore the prevalence of plasmid-mediated colistin resistance gene, mcr-1 in E. coli isolated from liver samples of dead poultry suspected of E. coli infections. The specimens were processed to isolate and identify E. coli; an antimicrobial susceptibility test (AST) using disk diffusion method was performed with 12 different antibiotics: Amikacin (30 μg), ampicillin (10 μg), ciprofloxacin (5 μg), chloramphenicol (30 μg), cefoxitin (30 μg), ceftazidime (30 μg), ceftriaxone (30 μg), cotrimoxazole (25 μg), gentamicin (10 μg), imipenem (10 μg), levofloxacin (5 μg) and tetracycline (30 μg).
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