總細菌與金黃色葡萄球菌在動物相關產業之暴露評估―文獻回顧與畜牧場調查

Abstract

近年來食品安全受到大眾的重視，食品生產過程之微生物汙染，包含會產生腸毒素導致食物中毒之金黃色葡萄球菌 (Staphylococcus aureus；S. aureus)，與感染後不易治療之抗藥性金黃色葡萄球菌 (Methicillin-resistant Staphylococcus aureus；MRSA)，對作為食物生產鏈源頭之畜牧場來說，更需重視這些微生物可能來帶來的危害。過去研究顯示畜牧場環境存在高濃度總細菌之粉塵，危害現場人員健康。而S. aureus與MRSA除了能在現場動物與人員身上檢出之外，也能在灰塵、空氣等環境樣本中檢測到，顯示總細菌、S. aureus與MRSA在畜牧場環境中傳播之風險。 因此本研究透過系統性文獻回顧的方式，彙整S. aureus與MRSA在畜牧場之陽性率、濃度以及影響因子。並對畜牧場進行實際現場調查，分別在現場清潔或消毒之前一天與後一天，收集乳牛場與養鴨場之高處與表面灰塵樣本，使用培養法與qPCR法，分析樣本中總活性細菌、總可培養性細菌、S. aureus濃度及MRSA陽性率，並探討其與現場特性之相關性，包含現場清潔消毒、不同舍別、環境因子與現場動物數量。 系統性文獻回顧之結果發現，動物鼻腔抹拭樣本之S. aurues陽性率，比起乳牛，小型反芻動物 (乳羊和乳山羊)之陽性率相對較高。而S. aurues除了可以在乳牛場擠奶儀器與環境地面檢出，在養豬場之空氣濃度可達103 CFU/m3。顯著影響S. aurues陽性率與濃度之因子包含動物年紀、採樣部位、季節、抗生素使用、動物數量等。而在MRSA的部分，豬隻相關場所之動物與人員樣本MRSA陽性率與主要基因型具有明顯之地域差異，歐洲地區MRSA陽性率偏高且基因型以ST398為主。而在亞洲地區之MRSA基因型以ST9為主，陽性率相對較低。在美洲與非洲大部分樣本為MRSA未檢出。顯著影響MRSA陽性率與濃度之因子包含畜牧場是否為集約模式 (集約代表動物飼養密度較高)、動物數量、現場清潔消毒、季節、抗生素使用等，且研究地點多以養豬場為主。 畜牧場現場採樣之分析結果，發現總活性細菌濃度的部分，無論是高處還是表面灰塵樣本，均為乳牛場高於養鴨場。另外乳牛場與養鴨場表面灰塵樣本並無MRSA檢出。在多變項分析結果中，廣義線性模型 (Generalized Linear Model, GLM)分析結果顯示，現場清潔消毒顯著降低乳牛場高處及表面灰塵，與養鴨場高處灰塵總活性細菌濃度，以及養鴨場表面灰塵總可培養性細菌濃度 (P<0.05)；總動物數量在乳牛場及養鴨場表面灰塵總活性細菌濃度log10值均達統計顯著 (P<0.05)；養鴨場表面灰塵總活性細菌濃度log10值與現場風速達統計顯著 (P=0.01，beta=0.83)、養鴨場表面灰塵總可培養性細菌濃度log10值與現場相對濕度達統計顯著 (P=0.02，beta=0.01)；高處灰塵之總活性細菌濃度log10值，分別與現場清潔消毒 (P<0.0001，beta=0.43)、舍別 (P<0.0001，beta=1.36)以及總動物數量 (P=0.049，beta=0.004)達統計顯著；而表面灰塵總活性細菌濃度log10值，分別與現場清潔消毒 (P=0.03，beta=0.13)、舍別 (P<0.0001，beta=1.82)、總動物數量 (P=0.009，beta=0.006)達統計顯著相關；邏輯迴歸分析結果則發現，表面灰塵之S. aureus檢出與否，與現場溫度達統計顯著 (P=0.026)。上述結果顯示現場清潔消毒、舍別與動物數量顯著影響環境中總細菌濃度，且本研究發現環境地面清潔與消毒，顯著降低乳牛場及養鴨場高處灰塵樣本總細菌濃度，但降低幅度有限，未能有效移除環境灰塵中大量的微生物。 本研究在台灣之乳牛場與養鴨場進行環境灰塵採樣，提供台灣畜牧場現場環境灰塵之總細菌及S. aureus濃度，並進一步探討其與環境特性之關聯性，發現現場清潔消毒、環境因子與動物數量對微生物之影響。

In recent years, food safety has been concerned by the public. Microbial contamination in the food production process, including the enterotoxins and antimicrobial resistance of S. aureus. Livestock farm as the source of the food production chain, more attention must be paid to the potential hazards caused by microorganisms. Researches showed that livestock farm workers are exposed to high levels of dust and bacteria, which lead to health effect. S. aureus and methicillin-resistant S. aureus (MRSA) not only found in livestock animal and workers, but also can be detected in environmental samples such as dust and air sample, indicating the risk of total bacteria, S. aureus and MRSA spreading in livestock farm environment. Thus, this study first coduct a systematic literature review, and assemble prevalence, concentration and influence factors of S. aureus and MRSA in livestock farm. Then, one duck farm and one dairy farm were selected to conduct field sampling. Environment dust sample were collected in animal farms in order to evaluate the concentration of total bacteria and S. aureus and prevalence of MRSA, then find out the factors such as disinfection and cleaning, different kinds of animal, environmental factors, and the number of animal whether it will affect the exposure indicators in animal farms or not. Systematic literature review found that the prevalence of S. aureus was higher in small ruminants such as dairy sheep and goats. S. aureus can also be detected in milking instruments and ground in dairy farms, and air concentration of S. aureus in pig farms can be up to 103 CFU/m3. Moreover, the age of animal, anatomic site of swab sampling, season, antimicrobial use, herd size, and etc. may affect the concentration and detection rate of S. aureus in animal farms. Besides, the prevalence and predominant sequence type (ST) of MRSA in pig-related place differs geographically. Prevalence of MRSA is high in Europe, and predominant sequence type is mainly ST398. Prevalence of MRSA in Asia is lower than Europe, and most stain belongs to ST9. Most of the sample were MRSA negative in America and Africa. Intensive farming or not, herd size, cleaning and disinfection, season, antimicrobial use, and etc. significantly affect the concentration and detection rate of MRSA in animal farms. And researches site were mainly pig farms. Field sampling in animal farms showed that total viable bacterial concentration of high-altitude and surface dust samples in dairy farm was higher than duck farm. And MRSA was not detected in the surface dust samples of dairy farm and duck farm. In the results of the multivariate analysis, generalized linear model (GLM) analysis showed that total viable bacterial concentration of high-altitude and surface dust samples in dairy farm and high-altitude dust samples in duck farm, and total culturable bacterial concentration of surface dust samples in duck farm were significantly correlated with cleaning and disinfection (P <0.05). Total viable bacterial concentration of surface dust samples in dairy and duck farm were significantly correlated with the number of animals (P<0.05). And total viable bacterial concentration of surface dust samples in duck farm was significantly correlated with field wind speed (P=0.01，beta=0.83). Moreover, total culturable bacterial concentration of surface dust samples in duck farm was significantly correlated with field relative humidity (P=0.02，beta=0.01). The GLM analysis also showed that total viable bacterial concentration of high-altitude dust samples was significantly correlated with cleaning and disinfection (P<.0001, beta=0.43), animal species (P<.0001, beta=1.36), and the number of animals (P=0.049, beta=0.004).The GLM analysis also showed that total viable bacterial concentration of surface dust samples was significantly correlated with cleaning and disinfection (P=0.03, beta=0.13), animal species (P<.0001, beta=1.82), and the number of animals (P=0.009, beta=0.006). Logistic regression analysis revealed that whether S. aureus was detected on the surface dust sample was statistically significant with the site temperature (P=0.026). In summary, total bacterial concentration of dust samples was significantly correlated with cleaning and disinfection, animal species, and the number of animals. Furthermore, cleaning and disinfection significantly reduced the total bacterial concentration of high-altitude dust samples in dairy and duck farm, but the reduction is limited, and failed to effectively remove a large number of microorganisms in environmental dust. This study conducted environmental sampling on dairy and duck farm in Taiwan, and evaluated the concentration of total bacteria and S. aureus and prevalence of MRSA, then find out the factors such as cleaning and disinfection, environmental factors, and the number of animal will affect the concentration of total bacteria and S. aureus in animal farms.