北台灣寵物及其畜主之金黃色葡萄球菌腸毒素之分子流行病學研究

Abstract

本研究針對台灣北部地區（台北市、台北縣、桃園縣），無金黃色葡萄球菌感染臨床症狀之寵物及其畜主之鼻腔以棉棒採樣，分離出金黃色葡萄球菌並檢測其腸毒素之基因型，並使用逆向被動乳膠凝集法（reverse passive latex agglutination, RPLA）檢測其傳統型腸毒素A、B、C、D、E之表現型，及使用限制酵素SmaI切割細菌之DNA後，進行脈衝式膠體電泳（Pulse-field gel electrophoresis, PFGE）分析菌株之相關性，並且作抗生素感受性試驗，以了解不同腸毒素基因型和抗藥性與其脈衝式膠體電泳分析分析結果之關係。結果共分離到116株金黃色葡萄球菌，之中有74株（63.8%）至少帶有一種腸毒素基因，最常被偵測到的腸毒素基因型為sea、seb、sek、sep、seq、egc等，另外，採集於人的分離株（95株）帶有腸毒素基因之比例（69.5%），顯著高於分離自寵物（狗與貓）之分離株（21株）（38.1%）（P < 0.05）。本研究分離得到的116株金黃色萄球菌中，鑑定出23株為抗methicillin金黃色葡萄球菌（Methicillin-resistant Staphylococcus aureus, MRSA），另外93株為對methicillin具感受性之金黃色葡萄球菌（Methicillin-sensitive Staphylococcus aureus, MSSA），並且MRSA有顯著高的比率帶有腸毒素基因（91.3%），MSSA的比率則較低（57%）（P < 0.01）。本研究有45.7%的分離株帶有與葡萄球菌性食物中毒有重要相關性的傳統型腸毒素基因型，這些菌株為引起葡萄球菌性食物中毒之可能潛在的危險因子。在脈衝式膠體電泳的相關性樹狀圖分析中，許多腸毒素基因如seb、sed、sek、sep、seq、egc可以發現帶有這些基因的菌株之間彼此可見有群聚現象，推測腸毒素的基因主要藉由菌株傳播（clonal spread）來散佈，因此特定的病原性菌株會有他們的地域性及族群分布特性，而脈衝式膠體電泳可能為病原株的追蹤有所助益。

In order to investigate the Staphylococcus aureus enterotoxin genotypes and phylogenetic relatedness, samples were collected with nasal swab from pet and their owners and using Pulse-field gel electrophoresis (PFGE) patterns of these isolates to analyze their phylogenetic relatedness with enterotoxin genotypes and antimicrobial susceptibility. The commercial RPLA test kit SET-RPLA detecting enterotoxins A, B, C, D, and E was available for this study to compare with the strain genotypes. The results of our previous sampling show that the strains of methicillin-resistant Staphylococcus aureus (MRSA) have a higher percentage (91.3%) of harboring enterotoxin genes than the methicillin-sensitive S. aureus (MSSA) do (57%) (P < 0.01), and the most frequent enterotoxin genotypes detected from free clinical complains pets and humans are sea, seb, sek, sep, seq and egc. To compare the se gene prevalence of isolates from human and pet, the human origins (66/95, 69.5%) were higher than the pet origins (8/21, 38.1%) (P < 0.05). Certain degree of relatedness between enterotoxin genotypes and PFGE phylogenetic dendrogram has been observed, and several enterotoxin genotypes, such as seb, sed, sek, sep, seq and egc have a trend to clump themselves into 60 - 100% cluster similarity. Perhaps that can explain why the distributions of se genes are variable with different origins and areas. Antimicrobial susceptivity test show that MRSAs had a higher resistance to the antibiotics than the MSSAs, and some resistance strains have high phylogenetic relatedness. As these results, S. aureus enterotoxin genes and antimicrobial resistance presents clustered appearance, for the reason that the pathogenic strains should also have their regional and clonal distribution and that would be helpful for tracing the source of pathogenic strain.