摘要
目标
本研究旨在调查从印度北部商品鸡泄殖腔拭子中分离的大肠杆菌中抗生素耐药性表型的发生，同时了解其遗传基础。
方法和结果
使用圆盘扩散技术评估大肠杆菌分离株对14种不同抗生素的易感性，并通过PCR筛选22个抗生素抗性基因（ARGs）的存在。分离株对氟喹诺酮类药物（萘啶酸91%、诺氟沙星73%和环丙沙星66%）、四环素（71%）、β-内酰胺类药物（氨苄青霉素49%和阿莫西林/克拉维酸37%）、复方三恶唑（48%）、链霉素（31%）和氯霉素（28%）具有高度耐药性；对头孢唑林（13%）、阿米卡星（10%）、氨曲南（4%）、庆大霉素（4%）和头孢曲松（3%）的耐药性相对较低。63%的分离株对四种以上的药物具有耐药性。在分离株中观察到大量质粒携带的ARGs，如tetA（83%）、sul3（44%）、aadA1（44%），strA（43%）、strB（41%）、qnrS（38%）、sul2（28%）和aac（6）-Ib‐cr（15%）。百分之四十五的分离株具有五种以上不同的ARG。gyrA和parC基因中的喹诺酮类耐药性决定区（QRDR）突变被发现是喹诺酮类耐药性的主要决定因素。QRDR突变包括回旋酶-A多肽中的leu83、asn87和gly87，以及拓扑异构酶IV（由parC编码）中的ile80和lys84。
结论
我们的研究结果表明，印度家禽行业滥用抗生素作为饲料添加剂和预防药物。它还将该行业规划为ARG复制和选择的活跃热点。
研究的意义和影响
我们的研究结果将为当局制定有效策略以限制抗生素在食用动物中作为非治疗剂的使用提供证据。质粒和染色体对喹诺酮类药物的耐药性的发生可以分别驱动耐药性表型在细菌物种之间的移动和耐药性沿细菌世代的垂直移动，这可能会带来缓解挑战。
Abstract
Aim
This study aimed to investigate the occurrence of antibiotic resistance phenotype and simultaneously understand its genetic basis in Escherichia coli isolated from the cloacal swabs of commercial chickens from north India.

Methods and Results
Escherichia coli isolates were assessed for susceptibility to 14 different antibiotics using the disc‐diffusion technique and were screened for the presence of 22 antibiotic resistance genes (ARGs) by employing PCR. Isolates were found to be highly resistant to fluoroquinolones (nalidixic acid 91%, norfloxacin 73% and ciprofloxacin 66%), tetracycline (71%), beta‐lactams (ampicillin 49% and amoxicillin/clavulanic acid 37%), co‐trimoxazole (48%), streptomycin (31%) and chloramphenicol (28%); and comparatively less resistant to cefazolin (13%), amikacin (10%), aztreonam (4%), gentamicin (4%) and ceftriaxone (3%). Sixty‐three percent of isolates were resistant to more than four different drugs. Abundance of plasmid‐borne ARGs like tetA (83%), sul3 (44%), aadA1 (44%), strA (43%), strB (41%), qnrS (38%), sul2 (28%) and aac(6)‐Ib‐cr (15%) was observed among the isolates. Forty‐five percent of isolates possessed more than five different ARGs. Quinolone resistance‐determining region (QRDR) mutations within gyrA and parC genes were found to be the major determiners of quinolone resistance. QRDR mutations included leu83, asn87 and gly87 within gyrase‐A polypeptide and ile80 and lys84 within topoisomerase IV (encoded by parC).

Conclusions
Our findings suggest the abuse of antibiotics as feed additives and prophylactic drugs in Indian poultry sector. It also projects this industry as an active hotspot for the replication and selection of ARGs.

Significance and Impact of the Study
Our findings would provide evidence to the authorities for formulating effective strategies for restricting antibiotic usage as non‐therapeutic agents in food animals. Occurrence of both plasmid‐borne and chromosome‐borne resistance towards quinolones can drive movement of resistance phenotype across bacterial species and vertical movement of resistance along the bacterial generations, respectively, which can pose mitigation challenges.

https://academic.oup.com/jambio/article-abstract/132/1/268/6716431?login=false