單核球增生李斯特菌於潮鯛生魚片生產廠之污染模式調查

Abstract

李斯特菌是一種會導致高住院率及死亡率的食媒性病原菌，是全球公共衛生的重要課題。而受汙染的水產品是重要媒介之一，雖然台灣目前並沒有因食用潮鯛產品導致李斯特菌症的案例發生，但許多國家已有因生魚產品遭受該菌汙染，並且導致李斯特菌症的報告。本研究對南部兩家漁產加工廠進行縱向性長期採樣調查，共計採樣件數3577件，總陽性率18.6% (664/3577)。其中2302份來自A廠，1275份來自B廠，A廠陽性率為19.0% (437/2302)，B廠陽性率為17.8% (227/1275)。不同季節對於潮鯛生魚片加工廠內的李斯特菌陽性率並沒有差異存在。潮鯛產地皆沒有分離到任何李斯特菌，陽性率為0% (0/128) ，潮鯛加工廠的陽性率為19.1% (653/3417)，上市魚產品的陽性率為34.4% (11/32) 。其中血清型最多的為4b (46.8%)，其次為1/2b (43.7%)。加工廠內各採樣區域的陽性率在A場最高為去內臟區 (24.3%)，其次為清洗消毒區 (23.6%)；B廠最高亦為去內臟區 (23.4%)，其次為放血去鱗區 (22.3%)。A廠之李斯特菌陽性率由開工前7.3%，開工後提高至22.8%，B廠之李斯特菌陽性率由開工前9.9%，開工後提高至28.2%，顯示兩家加工廠內確實具有汙染累積的情況發生，加工環境及設備確實為重要的汙染來源之一。 在分子生物學上，使用脈衝式電泳(Pulsed Field Gel Electrophoresis, PFGE) 判斷各分離菌株，以2種限制酶ApaI及AscI進行切割後，發現開工前加工環境設備分離到的菌株持續出現在加工廠內其他作業時間及作業點，此結果指出李斯特菌於加工廠內確實有交叉汙染的情形。 本調查結果指出臺灣潮鯛加工廠內及上市產品確實有李斯特菌汙染的情形，且分離到的菌株主要血清型1/2b及4b亦為人類李斯特菌症常見之血清型。民眾有可能食用遭受汙染之加工食品而感染李斯特菌，加工廠應改善清潔流程或增加清潔工作的次數，以防止李斯特菌的汙染。政府單位也應重視其相關問題，輔導業者維護清潔加工設備，以保障食品安全衛生。

Listeria monocytogenes has been recognized as an important public health problem. Due to its invasive nature it has caused the highest hospitalization and case-fatality rate of all the foodborne pathogens. Ready-to-eat (RTE) fish products contaminated by L. monocytogenes act as a critical vehicle transmitting to humans. We performed a 2-year study at two tilapia sashimi processing plants in southern Taiwan to locate possible contamination sources.Sampling was taken from the fish farm, transportation, processing plant and final products. Processing works in the processing plants were divided into five sections including freezing, bleeding and scaling, visceral removal, cleaning and disinfection, and packaging. Before reaching the processing plant, the first sampling was taken and continued every 2 hours until the processing ended.The total prevalence of L. monocytogenes was 18.6% (664/3577) with 19.0% (437/2302) in plant A and 17.8% (227/1275) in plant B. The predominant serotypes was 4b (46.8%) and 1/2b (43.7%). Seasonal conditions had no influence on the presence of bacteria. In the working sections, the isolation rates in plant A ranged from 1.5 to 24.3% whereas it was 9.9 to 23.4% in plant B. Among them, visceral removal was found to have the highest rate of contamination. Additionally, the isolation rates increased in plant A from the time point before processing (7.3%) to the 6th hour (22.8%). The highest isolation rate in plant B occurred at the last sampling time point (28.2%). As the processing started, the L. monocytogenes isolation rate increased in both plants. The phenomenon of accumulated contamination indicates that the environment and the facilities acted as vital sources of contamination during processing. Results of molecular subtyping PFGE suggest that cross-contamination of Listeria was occurring within the processing plant. Bacteria from the facilities were also found before the fish arrived. This indicates that the environment played an important role in the contamination. This study suggests that the sanitation procedures in the plants were inadequate. Plant managers should modify cleaning and sanitation procedures as a means of reducing and controlling microbial contamination.