Abstract: 【Objective】 To improve the isolation efficiency of Staphylococcus aureus (SA) from milk samples and rapidly assess the qualitative risk in provoking clinical mastitis caused by the isolates. 【Methods】 Targeted isolation of SA in milk sample was carried out using Staphylococcus selective medium and CHROM chromogenic media, and the quantitative determination of hemolysin method was established to evaluate the virulence of SA isolates. 【Results】 In the experiment, 27, 21 and 17 SA isolates were isolated respectively from 64 clinical mastitis milk samples, 157 subclinical mastitis milk samples and 213 healthy milk samples. Among these isolates, 9 (33.3%), 1 (4.8%) and 2 (11.8%) isolates had hemolysin secretion of more than 1,500 VH50 U/mL (virulent); 1 strain (4.8%), 13 strains (61.9%) and 4 strains (23.5%) had hemolysin secretion between 1,000 and 1,500 VH50 U/mL (Moderate virulent), respectively; 2 strains (11.8%), 7 strains (33.3%) and 11 strains (64.7%) had hemolysin secretion of less than 1,000 VH50 U/mL (weak virulence), respectively. Spearman rank correlation coefficient analysis showed that the occurrence of clinical mastitis was positively correlated with infection hemolysin secretion (> 1,000 VH50 U / mL) isolates (ρ= 1), and negatively correlated with infection hemolysin secretion < 1,000 VH50 U / mL (weakly virulent) strains (Ρ =-1). 【Significance】 SA targeted isolation method could improve the isolation efficiency and reflect the actual infection rate of SA in dairy farms. Quantitative determination of hemolysin could be used to evaluate the virulence of SA. The risk of clinical mastitis could be preliminarily predicted according to the infection situation of moderate and strong virulent isolates. In addition, it is feasible to improve the cure rate of SA clinical mastitis and reduce the spread of drug-resistant isolates by cooperating with clinical drug sensitivity test.

Key words: dairy cows; clinical mastitis; Staphylococcus aureus; targeted isolation; virulence evaluation

摘要： 【目的】研究奶牛养殖场中金黄色葡萄球菌(Staphylococcus aureus,SA)的分离效率,快速评估分离株致临床型乳腺炎的风险。【方法】使用葡萄球菌选择培养基结合CHROM SA显色培养基对乳样中的SA进行靶向分离,经斯皮尔曼等级相关系数分析,建立定量测定分泌性溶血素评价SA毒力的方法。【结果】对采集的64份临床型乳腺炎、157份隐性乳腺炎和213份健康乳样进行SA分离,从中分别分离出27株、21株和17株SA菌;对应样本分离株中,溶血素分泌量≥1 500 VH50 U/mL(强毒力)的菌株分别为9株(33.3%)、1株(4.8%)和2株(11.8%)、溶血素分泌量在1 000~1 500 VH50 U/mL(中等毒力)的菌株1株(4.8%)、13株(61.9%)和4株(23.5%)、溶血素分泌量<1 000 VH50 U/mL(弱毒力)的2株(11.8%)、7株(33.3%)和11株(64.7%)。临床型乳腺炎的发生与感染溶血素分泌量≥1 000 VH50 U/mL(中、强毒力)菌株呈正相关(ρ=1,P=0.006 9),与感染溶血素分泌量<1 000 VH50 U/mL(弱毒力)菌株呈负相关(ρ=-1,P=0.10)。【结论】靶向分离方法提高了SA分离效率,可真实反应奶牛养殖场中SA感染率;定量测定溶血素可用于SA毒力评价,根据中、强毒力菌株的感染情况可以初步预测临床型奶牛乳腺炎发生风险,配合临床药物敏感性试验有可能提高SA性临床型乳腺炎的治愈率,减少耐药株的扩散。

关键词: 奶牛, 临床型乳腺炎, 金黄色葡萄球菌, 靶向分离, 毒力评价