摘要
      新鲜蔬菜与食源性疾病的爆发密切相关；然而，我国对新鲜蔬菜微生物质量的系统分析和新鲜农产品食源性病原体的分子信息报道较少。在此，我们通过最可能数法评估了大肠杆菌的流行病学流行率，并对从中国陕西省零售新鲜蔬菜中回收的沙门氏菌和耐环丙沙星大肠杆菌进行了鉴定。进行了抗微生物药敏试验、血清型测定、多位点序列分型（MLST）、核心基因组多位点序列分类（cgMLST），抗生素耐药性编码基因（ARG）注释、毒力因子预测和功能分类。在2020年10月至2021年9月期间，576份样本（即西红柿、生菜、菠菜和卷心菜）被发现大肠菌群呈阳性，大肠菌群的流行呈季节性趋势。西安市超市蔬菜大肠菌群显著低于其他城市（P<0.01）。沙门氏菌和CIPR大肠杆菌阳性蔬菜的检出率分别为1%（6/576）和0.7%（4/576）。所有分离株均表现出对≥1种抗生素的耐药性，92.9%（13/14）具有多重耐药性。菠菜中一株产超广谱β-内酰胺酶（ESBL）的CIPR大肠杆菌不仅对三种第三代头孢菌素具有耐药性，而且对两种多粘菌素也具有耐药性。在9个沙门氏菌分离株中，鉴定出5种不同的血清型（肠炎沙门氏菌、印第安纳沙门氏菌，鼠伤寒沙门氏菌的单相变体、阿戈纳沙门氏菌和Gallinarum沙门氏菌）、4种序列型（ST；ST11、ST13、ST17和ST34）和7种核心基因组ST（cgST）。将5株CIPR大肠杆菌分为3个血清型（O101:H4、O8:H18和O11:H25）、3个ST（ST44、ST48和ST457）和4个cgST。在喹诺酮类耐药性决定区（QRDR）中，ParC中Thr57Ser/Ser80Arg和GyrA中Ser83Phe/Asp87Gly的氨基酸突变共存可能是萘啶酸耐药性的原因。在8个血清型中鉴定出8个明确的毒力谱。值得注意的是，cdtB和pltA仅编码伤寒毒素，仅从S.Indiana中检测到伤寒分离株，并首次在新鲜蔬菜中检测到与猪食物链密切相关的单相鼠伤寒分离株。总之，我们的研究结果表明，该省新鲜蔬菜上的大肠菌群污染很普遍。大多数沙门氏菌和CIPR大肠杆菌分离株具有表型和遗传多样性，可以通过携带多种ARG和毒力基因来抵抗多种抗生素。
Abstract
Fresh vegetables are closely associated with foodborne disease outbreaks; however, systematic analysis of the microbiological quality of fresh vegetables and molecular information on foodborne pathogens in fresh produce are poorly reported in China. Here, we evaluated the epidemiological prevalence of coliforms via the most probable number method and characterized Salmonella and ciprofloxacin-resistant (CIPR) Escherichia coli isolates recovered from retail fresh vegetables in Shaanxi Province, China. Antimicrobial susceptibility testing, serotype determination, multilocus sequence typing (MLST), core genome multilocus sequence typing (cgMLST), antibiotic resistance encoding gene (ARG) annotation, virulence factor prediction, and functional classification were performed. Between October 2020 and September 2021, 576 samples (i.e., tomatoes, lettuces, spinaches, and cabbages) were found to be positive for coliforms, and the prevalence of coliforms showed a seasonal trend. Coliform counts of vegetables in supermarkets in Xi'an were significantly lower (P < 0.01) than that in other cities. The detection rates of Salmonella and CIPR E. coli-positive vegetables were 1 % (6/576) and 0.7 % (4/576), respectively. All isolates exhibited resistance to ≥1 antibiotics, and 92.9 % (13/14) were multidrug-resistant. One extended spectrum β-lactamase (ESBL)-producing CIPR E. coli isolate in spinach was resistant to not only three third-generation cephalosporins but also to two polymyxins. Among nine Salmonella isolates, five different serovars (S. Enteritidis, S. Indiana, monophasic variant of S. Typhimurium, S. Agona, and S. Gallinarum), four sequence types (STs; ST11, ST13, ST17, and ST34), and seven core genome STs (cgSTs) were identified. Five CIPR E. coli strains were assigned to three serovars (O101:H4, O8:H18, and O11:H25), three STs (ST44, ST48, and ST457), and four cgSTs. Coexisting amino acid mutations of Thr57Ser/Ser80Arg in ParC and Ser83Phe/Asp87Gly in GyrA in quinolone resistance-determining regions (QRDRs) might be causes for nalidixic acid resistance. Eight definite virulence profiles in eight serovars were identified. Notably, cdtB and pltA only encoded typhoid toxins and were just detected from S. Typhoid isolates were also detected from S. Indiana and monophasic S. Typhimurium, which are closely associated with swine food chain were first detected in fresh vegetables. In conclusion, our findings suggest that coliform contamination on fresh vegetables is prevalent in this province. Most Salmonella and CIPR E. coli isolates were phenotypically and genetically diverse and could resist multiple antibiotics by carrying multiple ARGs and virulence genes.

https://www.sciencedirect.com/science/article/abs/pii/S0168160522005256