Department of Microbiology and Plant Pathology, University of Pretoria, Main Campus, Hatfield, Pretoria, 0002 South Africa.
J Food Prot. 2015 Apr;78(4):643-51. doi: 10.4315/0362-028X.JFP-14-486.
The potential transfer of human pathogenic bacteria present in irrigation water onto fresh produce was investigated, because surface water sources used for irrigation purposes in South Africa have increasingly been reported to be contaminated with enteric bacterial pathogens. A microbiological analysis was performed of a selected river in Limpopo Province, South Africa, that is often contaminated with raw sewage from municipal sewage works and overhead irrigated onions produced on a commercial farm. Counts of Escherichia coli, coliforms, aerobic bacteria, fungi, and yeasts and the prevalence of E. coli O157:H7, Salmonella, and Listeria monocytogenes were determined. Identities of bacterial isolates from irrigation water and onions were confirmed using matrix-assisted laser desorption ionization-time of flight mass spectrometry, PCR, and biochemical tests. To establish a potential link between the microbiological quality of the irrigation source and the onions, the E. coli isolates from both were subjected to antibiotic resistance, virulence gene, and enterobacterial repetitive intergenic consensus PCR analyses. River water E. coli counts exceeded South African Department of Water Affairs and World Health Organization irrigation water guidelines. Counts of aerobic bacteria, coliforms, fungi, and yeasts of onions from the market were acceptable according to Department of Health Directorate, Food Control, South Africa, microbiological guidelines for ready-to-eat fresh fruits and vegetables. E. coli O157:H7, Salmonella, and L. monocytogenes were not detected in onions, whereas only Salmonella was detected in 22% of water samples. Matrix-assisted laser desorption ionization-time of flight mass spectrometry and PCR identification of E. coli isolates from water and onions correlated. Of the 45 E. coli isolates from water and onions, 42.2% were resistant to multiple antibiotics. Virulence genes eae, stx1, and stx2 were detected in 2.2, 6.6, and 2.2% of the E. coli isolates, respectively. Phenotypic (antimicrobial) and genotypic (virulence gene prevalence, DNA fingerprinting) analyses showed a link between river, dam, irrigation pivot point, and onion E. coli isolates.
本研究调查了灌溉水中存在的人类致病菌转移到新鲜农产品上的潜力，因为南非用于灌溉的地表水水源中越来越多地被报道受到肠细菌病原体的污染。对南非林波波省的一条河流进行了微生物分析，该河流经常受到来自城市污水处理厂的未经处理的污水和商业农场上空灌溉洋葱的污染。对大肠杆菌、大肠菌群、需氧菌、真菌和酵母菌的数量以及大肠杆菌 O157:H7、沙门氏菌和李斯特菌的流行情况进行了测定。使用基质辅助激光解吸电离飞行时间质谱、PCR 和生化试验确认了灌溉水和洋葱中细菌分离株的身份。为了确定灌溉水源和洋葱的微生物质量之间的潜在联系，将来自两者的大肠杆菌分离株进行了抗生素耐药性、毒力基因和肠杆菌重复基因间一致性 PCR 分析。河水大肠杆菌的数量超过了南非水务局和世界卫生组织的灌溉水指南。根据南非卫生部食品控制署的微生物指南，市场上洋葱的需氧菌、大肠菌群、真菌和酵母菌数量可接受，用于即食新鲜水果和蔬菜。洋葱中未检测到大肠杆菌 O157:H7、沙门氏菌和李斯特菌，但只有 22%的水样中检测到沙门氏菌。水和洋葱中大肠杆菌分离株的基质辅助激光解吸电离飞行时间质谱和 PCR 鉴定结果相关。在来自水和洋葱的 45 株大肠杆菌分离株中，有 42.2%对多种抗生素具有耐药性。在 2.2%、6.6%和 2.2%的大肠杆菌分离株中分别检测到 eae、stx1 和 stx2 毒力基因。表型（抗菌）和基因型（毒力基因流行率、DNA 指纹图谱）分析表明，河流、水坝、灌溉枢轴点和洋葱大肠杆菌分离株之间存在联系。
