台灣北部地區豬隻肉品市場與屠宰場之抗Methicillin金黃色葡萄球菌分析

Abstract

抗methicillin金黃色葡萄球菌 (methicillin-resistant Staphlococcus aureus; MRSA) 為現今社會的一重要病原，近年來有許多關於畜產相關型 (Livestock-associated, LA) MRSA的報導，更為人畜共處環境中的潛在風險，尤其是豬隻相關環境，以北美與歐洲盛行之ST398與亞洲較常分離出之ST9有更多的報告。本研究由肉品市場及屠宰場豬隻鼻腔取樣以進行LA-MRSA的盛行率調查與特性分析。使用的分型法有脈衝式膠體電泳法 (pulsed-field gel electrophoresis; PFGE) 與以PCR為基礎之鑑定法，包含multilocus sequence typing (MLST)、SCCmec typing與spa-typing。總共採集了299頭豬隻鼻腔樣本，MRSA攜帶比例為42.5% (127/299)，菌株皆為PVL gene陰性，且皆歸類於MLST ST9；依PFGE相關性分析，將166株MRSA以相似度在71%以上的條件下，摒除了一株無法用SmaI切割的菌株，可區分為5個clusters，其中有36 頭豬 (28.3%) 攜帶有2株以上分屬不同pulso-type的MRSA；SCCmec分型主要為V型 (96.4%)，另有IV型與無法鑑定的菌株；超過90%菌株的spa-typing型別為t899，另有t1939、t2922、t4132、t4358、t7616及1株無法鑑定的菌株，其中t7616是首先被發現的spa-型別。Agar Breakpoint Method結果，所有菌株對clindamycin (100%)有抗性，對ciprofloxacin (98.8%)、erythromycin (83.7%)、gentamicin (99.4%)、tetracycline (99.4%)、trimethoprim-sulfamethoxazole (90.0%)等亦皆具高度抗藥性，菌株抗藥性低於50%的藥物有chloramphenicol (42.2%) 與rifampin (13.3%)，對vancomycin皆具敏感性 (100%)；而Micro-broth Dilution Method結果，對chloramphenicol抗性比例為78.9%，rifampin為1.8%。以本研究結論，台灣最盛行的LA-MRSA型別為ST9，與某些亞洲國家之調查相同，但不是歐美盛行株ST398；畜產環境中存在於豬隻身上高盛行率且具多重抗藥性的MRSA應進一步監控，並管理相關風險。

Increasing prevalence of livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) has been described in many countries recently, such as ST398 in Europe and North America, while ST9 has been detected from swine and workers in Asia areas, such as China and Malaysia. In total, 299 swine nasal samples were collected from a meat market and a slaughterhouse in this study. Molecular techniques including multilocus sequence typing (MLST), pulse-field gel electrophoresis (PFGE), and staphylococcal chromosomal cassette mec (SCCmec) typing were applied to characterize MRSAs. The prevalence of MRSA was 42.5% (127/299). All isolates were PVL negative, and were assigned as MLST ST9. According to PFGE results, a total of 166 MRSAs were recovered. Five clusters of pulso-types were grouped with similarity of all higher than 71%, except a SmaI non-typeable strain. Thirty-six pigs (28.3%) harbored more than one MRSA strain which shared same PFGE results. The majority of the isolates (160) belonged to SCCmec type V, and 4 others were type IV, and the rest two were SCCmec non-typeable. Among spa typing, more than 90% of isolates were t899, the rest were t1939, t2922, t4132, t4358, a novel type- t7616, and a non-spa-typeable isolate. In the result of agar breakpoint method, all MRSAs were susceptible to vancomycin and resistant to clindamycin. There were more than 80% of isolates resistant to gentamicin (99.4%), tetracycline (99.4%), ciprofloxacin (98.8%), trimethoprim-sulfamethoxazole (90.0%), erythromycin (83.7%), and less than 50% to chloramphenicol (42.2%) and rifampin (13.3%). Among micro-broth dilution method, the percentage of chloramphenicol resistance was 78.9%, and rifampin resistance was 1.8%.In conclusions, high prevalence of LA-MRSA ST9 was found and the isolates were the same as those reported in some Asia countries. High prevalence of MRSA with multidrug resistance in livestock deserves public health concerns for workers in swine-associated environments.