Institute for Food Safety and Hygiene, Vetsuisse Faculty University of Zurich, 8057 Zurich, Switzerland.
Institute for Food Safety and Hygiene, Vetsuisse Faculty University of Zurich, 8057 Zurich, Switzerland.
J Dairy Sci. 2019 Apr;102(4):3274-3281. doi: 10.3168/jds.2018-15317. Epub 2019 Feb 22.
Staphylococcus aureus can be associated with subclinical, acute, chronic, and toxic cases of bovine intramammary infections, leading to considerable financial losses for the dairy industry in Switzerland and worldwide. In addition, milk products are one of the most common food categories implicated in staphylococcal food poisoning in humans. Detailed information on the population structure, as well as the virulence and resistance characteristics of Staph. aureus originating from bovine mastitis milk is needed to allow for source attribution and risk assessment of Staph. aureus in a food poisoning context and to improve therapeutic approaches in cattle. Our objective was to assess the population structure, phenotypic resistance patterns, and virulence and resistance gene profiles of Staph. aureus isolates from bovine mastitis milk in Switzerland. To this end, 58 Staph. aureus strains were characterized. The DNA microarray was used to test for the presence or absence of virulence and resistance genes. In addition, minimum inhibitory concentrations of various antimicrobial agents were determined by microdilution. To assess the population structure of the isolates, we determined clonal complexes (CC) using DNA microarray hybridization profiles and performed multilocus sequence typing and spa typing. The strains were assigned to 7 clonal complexes, 10 sequence types, and 11 spa types, with CC705 (43%), CC97 (33%), and CC20 (12%) representing the most common lineages and t529 (43%) and t267 (21%) representing the most common spa types. Only 1 isolate was assigned to CC8, a clonal lineage linked to high within-herd prevalence of mastitis. A total of 14% (n = 8) of strains were classified as resistant to penicillin, and 1 strain each was classified as oxacillin and pirlimycin resistant. Although no clinical breakpoints are available for the combination of kanamycin/cefalexin, growth of all strains was inhibited by the lowest combination of kanamycin/cefalexin concentrations tested (4 µg/mL of kanamycin and 0.4 µg/mL of cefalexin). One strain assigned to CC20, ST389, and t2094 exhibited resistance to penicillin, oxacillin, and pirlimycin as well as intermediate susceptibility to erythromycin and high minimum inhibitory concentration for several antimicrobial agents, for which no breakpoints were available.
金黄色葡萄球菌可与亚临床、急性、慢性和中毒性牛乳腺炎感染相关，给瑞士乃至全球的乳品行业带来巨大的经济损失。此外，乳制品是引发人类金黄色葡萄球菌食物中毒的最常见食品类别之一。详细了解源自牛乳腺炎牛奶的金黄色葡萄球菌的种群结构、毒力和耐药特征，有助于对金黄色葡萄球菌食物中毒进行溯源和风险评估，并改进牛的治疗方法。我们的目的是评估瑞士牛乳腺炎牛奶中金黄色葡萄球菌分离株的种群结构、表型耐药模式以及毒力和耐药基因谱。为此，我们对 58 株金黄色葡萄球菌菌株进行了特征描述。使用 DNA 微阵列检测毒力和耐药基因的存在或缺失。此外，通过微量稀释法确定了各种抗菌药物的最低抑菌浓度。为了评估分离株的种群结构，我们使用 DNA 微阵列杂交图谱确定了克隆复合体（CC），并进行了多位点序列分型和 spa 分型。这些菌株被分配到 7 个克隆复合体、10 个序列类型和 11 个 spa 类型，其中 CC705（43%）、CC97（33%）和 CC20（12%）代表最常见的谱系，t529（43%）和 t267（21%）代表最常见的 spa 类型。只有 1 株被分配到 CC8，这是一个与乳腺炎高场内流行率相关的克隆谱系。共有 14%（n=8）的菌株被归类为青霉素耐药，1 株分别被归类为耐苯唑西林和吡利霉素。虽然没有针对卡那霉素/头孢氨苄联合用药的临床折点，但所有菌株的生长均被测试的最低卡那霉素/头孢氨苄浓度组合（4μg/ml 卡那霉素和 0.4μg/ml 头孢氨苄）所抑制。一株被分配到 CC20、ST389 和 t2094 的菌株对青霉素、苯唑西林和吡利霉素耐药，对红霉素中介敏感，对几种无折点的抗菌药物的最低抑菌浓度较高。
