Department of Nutrition and Food Science, University of Ghana, Accra, Ghana.
Department of Veterinary Medicine, University of Cambridge, United Kingdom.
Int J Food Microbiol. 2018 Jul 20;277:41-49. doi: 10.1016/j.ijfoodmicro.2018.04.025. Epub 2018 Apr 14.
Consumer perception of poor hygiene of fresh milk products is a major barrier to promotion of milk consumption as an intervention to alleviate the burden of malnutrition in Ghana. Fresh milk is retailed raw, boiled, or processed into unfermented cheese and spontaneously fermented products in unlicensed outlets. In this study, we have determined microbiological quality of informally retailed fresh milk products and characterized the genomic diversity and antimicrobial resistance (AMR) patterns of non-typhoidal Salmonella (NTS) in implicated products. A total of 159 common dairy products were purchased from five traditional milk markets in Accra. Samples were analysed for concentrations of aerobic bacteria, total and fecal coliforms, Escherichia coli, staphylococci, lactic acid bacteria and yeast and moulds. The presence of Salmonella, E. coli O157:H7, Listeria monocytogenes and Staphylococcus aureus were determined. AMR of Salmonella against 18 antibiotics was experimentally determined. Genome sequencing of 19 Salmonella isolates allowed determination of serovars, antigenic profiles, prediction of AMR genes in silico and inference of phylogenetic relatedness between strains. Raw and heat-treated milk did not differ significantly in overall bacterial quality (P = 0.851). E. coli O157:H7 and Staphylococcus aureus were present in 34.3% and 12.9% of dairy products respectively. Multidrug resistant (MDR) Salmonella enterica serovars Muenster and Legon were identified in 11.8% and 5.9% of unfermented cheese samples respectively. Pan genome analysis revealed a total of 3712 core genes. All Salmonella strains were resistant to Trimethoprim/Sulfamethoxazole, Cefoxitin, Cefuroxime Axetil and Cefuroxime. Resistance to Chloramphenicol (18%) and Ciprofloxacin (100%), which are first line antibiotics used in treatment of NTS bacteremia in Ghana, was evident. AMR was attributed to presence and/or mutations in the following genes: golS, sdiA for cephalosporins, aac(6')-Iy, ant(9) for aminoglycosides, mdtK, gyrA, gyrB, parC, parE for quinolones and cat1, cat4 for phenicols. Phylogenetic analysis based on accessory genes clustered S. Legon strains separately from the S. Muenster strains. These strains were from different markets suggesting local circulation of related strains. Our study justifies consumer resistance to consumption of unripened soft cheese without further lethal heat treatment, and provides evidence that supports the Ghana Health Service recommendation for use of 3rd generation cephalosporins for the treatment of MDR NTS infections.
消费者对新鲜奶制品卫生状况的认知是推广牛奶消费以缓解加纳营养不良负担的主要障碍。新鲜牛奶在未经许可的摊位上以生奶、煮沸奶或加工成未经发酵的奶酪和自然发酵产品的形式零售。在这项研究中，我们已经确定了非正规销售的新鲜奶制品的微生物质量，并对相关产品中的非伤寒沙门氏菌（NTS）的基因组多样性和抗生素耐药性（AMR）模式进行了特征描述。从阿克拉的五个传统牛奶市场购买了 159 种常见乳制品。样品分析了需氧细菌、总大肠菌群和粪便大肠菌群、大肠杆菌、葡萄球菌、乳酸菌和酵母及霉菌的浓度。检测了沙门氏菌、大肠杆菌 O157:H7、单核细胞增生李斯特菌和金黄色葡萄球菌的存在情况。通过实验确定了沙门氏菌对 18 种抗生素的耐药性。对 19 株沙门氏菌分离株进行基因组测序，可确定血清型、抗原谱，预测体内的 AMR 基因，并推断菌株之间的系统发育关系。生奶和热处理奶在总体细菌质量方面无显著差异（P=0.851）。大肠杆菌 O157:H7 和金黄色葡萄球菌分别存在于 34.3%和 12.9%的乳制品中。在未发酵奶酪样本中分别发现了 11.8%和 5.9%的多重耐药（MDR）沙门氏菌肠炎血清型门斯特和莱贡。泛基因组分析共发现 3712 个核心基因。所有沙门氏菌菌株均对甲氧苄啶/磺胺甲恶唑、头孢西丁、头孢呋辛酯和头孢呋辛耐药。对氯霉素（18%）和环丙沙星（100%）的耐药性明显，氯霉素和环丙沙星是加纳用于治疗 NTS 菌血症的一线抗生素。耐药性归因于以下基因的存在和/或突变：头孢菌素的 golS、sdiA，氨基糖苷类的 aac(6')-Iy、ant(9)，喹诺酮类的 mdtK、gyrA、gyrB、parC、parE 和酚类的 cat1、cat4。基于辅助基因的系统发育分析将 S. Legon 菌株与 S. Muenster 菌株分开聚类。这些菌株来自不同的市场，表明相关菌株在当地循环。我们的研究证明了消费者对未经成熟的软奶酪的抵制，在未经进一步致命热处理的情况下，消费者不会食用这些奶酪，并提供了支持加纳卫生服务部门建议使用第三代头孢菌素治疗多重耐药 NTS 感染的证据。
