Australian Centre for Antimicrobial Resistance Ecology, School of Animal and Veterinary Sciences, The University of Adelaide, Roseworthy, Australia; Research Centre for Infectious Diseases, School of Biological Sciences, The University of Adelaide, Adelaide, Australia.
Department of Primary Industries, New South Wales Government, Wollongbar, Australia.
Int J Food Microbiol. 2021 Feb 16;340:109042. doi: 10.1016/j.ijfoodmicro.2021.109042. Epub 2021 Jan 5.
The development of antimicrobial resistance in foodborne pathogens is a growing public health concern. This study was undertaken to determine the antimicrobial susceptibility of Salmonella enterica subspecies enterica isolated from the Australian commercial egg layer industry. S. enterica subspecies enterica (n=307) isolated from Australian commercial layer flock environments (2015-2018) were obtained from reference, research and State Government laboratories from six Australian states. All Salmonella isolates were serotyped. Antimicrobial susceptibility testing (AST) for 16 antimicrobial agents was performed by broth microdilution. Antimicrobial resistance genes and sequence types (STs) were identified in significant isolates by whole genome sequencing (WGS). Three main serotypes were detected, S. Typhimurium (n=61, 19.9%), S. Senftenburg (n=45, 14.7%) and S. Agona (n=37, 12.1%). AST showed 293/307 (95.4%) isolates were susceptible to all tested antimicrobial agents and all isolates were susceptible to amoxicillin-clavulanate, azithromycin, ceftiofur, ceftriaxone, ciprofloxacin, colistin, florfenicol, gentamicin, kanamycin and trimethoprim-sulfamethoxazole. Low levels of non-susceptibility were observed to streptomycin (2.3%, n=7), sulfisoxazole (2.0%, n=6), chloramphenicol (1.3%, n=4) and tetracycline (1.0%, n=3). Very low levels of non-susceptibility were observed to ampicillin (2/307; 0.7%) and cefoxitin (2/307; 0.7%). Two isolates (S. Havana and S. Montevideo), exhibited multidrug-resistant phenotypes to streptomycin, sulfisoxazole and tetracycline and possessed corresponding antimicrobial resistance genes (aadA4, aac(6')-Iaa, sul1, tetB). One S. Typhimurium isolate was resistant to ampicillin and tetracycline, and possessed both tetA and bla. WGS also identified these isolates as belonging to ST4 (S. Montevideo), ST578 (S. Havana) and ST19 (S. Typhimurium). The absence of resistance to highest priority critically important antimicrobials as well as the extremely low level of AMR generally among Australian commercial egg layer Salmonella isolates likely reflect Australia's conservative antimicrobial registration policy in food-producing animals and low rates of antimicrobial use within the industry.
食源性病原体中抗菌药物耐药性的发展是一个日益严重的公共卫生问题。本研究旨在确定从澳大利亚商业蛋鸡产业中分离出的肠炎沙门氏菌亚种肠炎沙门氏菌的抗菌药物敏感性。从澳大利亚六个州的参考、研究和州政府实验室获得了 2015-2018 年从澳大利亚商业蛋鸡群环境中分离出的肠炎沙门氏菌亚种肠炎沙门氏菌（n=307）。对所有沙门氏菌分离株进行血清分型。采用肉汤微量稀释法对 16 种抗菌药物进行抗菌药物敏感性试验（AST）。通过全基因组测序（WGS）鉴定重要分离株中的抗菌药物耐药基因和序列型（ST）。检测到三种主要血清型，鼠伤寒沙门氏菌（n=61，19.9%）、肠炎沙门氏菌（n=45，14.7%）和肠炎沙门氏菌（n=37，12.1%）。AST 显示 293/307（95.4%）分离株对所有测试的抗菌药物均敏感，所有分离株均对阿莫西林-克拉维酸、阿奇霉素、头孢噻呋、头孢曲松、环丙沙星、黏菌素、氟苯尼考、庆大霉素、卡那霉素和复方磺胺甲噁唑敏感。对链霉素（2.3%，n=7）、磺胺二甲嘧啶（2.0%，n=6）、氯霉素（1.3%，n=4）和四环素（1.0%，n=3）的非敏感性观察到低水平。对氨苄西林（2/307；0.7%）和头孢西丁（2/307；0.7%）的非敏感性观察到极低水平。两株分离株（哈瓦那沙门氏菌和蒙得维的亚沙门氏菌）对链霉素、磺胺二甲嘧啶和四环素表现出多药耐药表型，并携带相应的抗菌药物耐药基因（aadA4、aac(6')-Iaa、sul1、tetB）。一株鼠伤寒沙门氏菌分离株对氨苄西林和四环素耐药，同时携带 tetA 和 bla。WGS 还鉴定这些分离株属于 ST4（蒙得维的亚沙门氏菌）、ST578（哈瓦那沙门氏菌）和 ST19（鼠伤寒沙门氏菌）。澳大利亚商业蛋鸡沙门氏菌分离株对高优先级关键抗菌药物无耐药性，且抗菌药物耐药性总体水平极低，这可能反映了澳大利亚在食用动物中对抗菌药物的注册政策较为保守，以及该行业中抗菌药物的使用率较低。
