泌尿道致病性大腸桿菌於鮮榨果汁之定量微生物暴露評估及其控制措施

Abstract

新鲜現榨果汁在飲用前通常未經滅菌或其他加熱處理，因此容易受到微生物污染。泌尿道致病性大腸桿菌（uropathogenic Escherichia coli, UPEC）是導致泌尿道感染（urinary tract infections, UTIs）的主要病原菌之一，佔感染病例65%至75%，被視為為新興的食源性病原菌。雖然UPEC傳統上多檢出自禽肉及其他肉類相關產品，但近年研究指出其亦可存在於新鮮蔬果中。然而，目前有關UPEC在果汁中的行為特性及其相關暴露風險的研究仍十分有限，故本研究旨在：(i) 調查臺灣市售現榨果汁中UPEC之污染情形，以識別具有較高UPEC污染風險之果汁類別；(ii) 針對高風險果汁（如甘蔗汁）建立定量微生物暴露評估，以量化消費者攝入UPEC之風險；以及 (iii) 建立UPEC於甘蔗汁中的熱失活模型，以提供可行之控制措施。

本研究自位於臺北市與新北市的飲料店、傳統市場及路邊攤，共收集120件新鲜現榨果汁樣品（包括：蘋果汁、芭樂汁、甘蔗汁及西瓜汁）進行微生物檢驗，項目包含生菌數、大腸桿菌群、以及大腸桿菌；並將疑似大腸桿菌之菌株進行分離以及鑑定。UPEC之鑑定以聚合酶連鎖反應（polymerase chain reaction, PCR）測定大腸桿菌分離菌株帶有的特定基因（c3509、c3686、chuA），確認為UPEC之菌株會再以PCR鑑定其帶有的毒力基因以及演化分型基因。結果顯示，甘蔗汁呈現最高之UPEC檢出率（9/30，30%）；自果汁分離之UPEC以演化型B1為主（12/33，36.2%），其次為演化型B2（11/33，33.3%）。而UPEC帶有的毒力基因則以fimH （26/33，78.8%）為檢出率最高，其次為毒力基因ompT（17/33，51.5%）。

根據採樣結果，市售現榨果汁中UPEC的檢出率以甘蔗汁為最高，故本研究選定甘蔗汁作為暴露風險評估與建立熱失活模型與之研究對象。本研究將微生物檢測數據整合至定量微生物暴露評估中，並透過Monte Carlo模擬（10,000次迭代）量化消費者攝食每份甘蔗汁超過不同UPEC濃度（5–8 log CFU/serving）的暴露機率。結果顯示，消費者攝入高劑量UPEC（>8 log CFU/serving）的機率為0.9%。敏感性分析指出，販售期間的儲存溫度為最具影響力之因素，而干預情境模擬結果則顯示若將零售陳列時間限縮於4或7小時內，可將暴露風險降低40%至90%。

透過建立UPEC於48、53、58、63 及 68 °C 下，在甘蔗汁以及添加檸檬酸的甘蔗汁中的熱失活模型。結果顯示，熱失活模型以Weibull模型描述為最佳。甘蔗汁中添加檸檬酸會導致UPEC耐熱性降低；且模型驗證於60 °C之結果顯示，該模型具有良好預測能力。故本研究估算了不同溫度條件下降低5至7 log菌量所需之加熱時間，可作為果汁製備及熱處理過程之安全設定參考依據。

綜上所述，本研究首次整合了臺灣本土甘蔗汁中UPEC之微生物採樣資料與暴露風險評估結果，並建立其熱失活預測模型，以凸顯有效的加熱方式與改善零售操作條件對提升產品微生物安全的重要性。本研究成果可作為此類未經滅菌處理之新鮮製備果汁，在微生物風險管理策略上之科學依據與參考建議，並有助於降低新興食源性UPEC感染對公共衛生之威脅。

Freshly prepared fruit juices are typically consumed without undergoing thermal processing, thereby increasing their susceptibility to microbial contamination. Uropathogenic Escherichia coli (UPEC), a primary etiological agent of urinary tract infections (UTIs), has increasingly been recognized as a potential foodborne pathogen. Although UPEC has been predominantly linked to poultry and meat-derived products, accumulating evidence suggests its occurrence in fresh produce. However, limited data are available regarding its distribution, survival characteristics, and associated exposure risks within fruit juice. Therefore, this study aimed to (i) investigate the prevalence of UPEC in freshly prepared fruit juices retailed in Taiwan; (ii) quantify consumer exposure risks associated with UPEC exposure through high-risk juice (sugarcane juice) consumption via quantitative microbial exposure assessment (QMEA); and (iii) establish the thermal inactivation model of UPEC in juice with high-risk (sugarcane juice) to inform feasible intervention strategies.

A total of 120 freshly prepared fruit juice samples, including apple, guava, sugarcane, and watermelon juices, were purchased from beverage shops, traditional markets, and street vendors across Taipei and New Taipei City. Microbiological analyses included enumeration of total aerobic bacteria, coliforms, and E. coli, followed by isolation of presumptive E. coli colonies. UPEC identification was performed using polymerase chain reaction (PCR) targeting specific genes (c3509, c3686, and chuA). Confirmed UPEC isolates were subsequently characterized for virulence-associated and phylogenetic genes to assess their uropathogenic potential. Among these, sugarcane juice had the highest prevalence of UPEC (30%, 9/30). Among the UPEC isolates, phylogenetic group B1 was predominant (12/33, 36.2%), followed by group B2 (11/33, 33.3%). The most frequently detected virulence genes were fimH (26/33, 78.8%), followed by ompT (17/33, 51.5%).

Given its comparatively higher prevalence of UPEC among freshly prepared fruit juices, sugarcane juice was selected as the target matrix for subsequent inactivation modeling and exposure assessment. The exposure assessment of UPEC in sugarcane juice was performed by integrating the data obtained from the microbial sampling, and a Monte Carlo simulation (10,000 iterations) was conducted . The probability of exposure exceeding potential UPEC thresholds (5–8 log CFU/serving) was quantified. The model predicted a 0.9% probability of high-level exposure (>8 log CFU/serving). Sensitivity analysis identified retail storage temperature as the most influential factor affecting exposure probability. Scenario simulations further indicated that reducing retail display time to 4 to 7 h could reduce exposure risk by up to 40–90%.

Thermal inactivation experiments were conducted in sugarcane juice and citric acid-supplemented sugarcane juice at 48, 53, 58, 63, and 68 °C. The resulting survival data were best described by the Weibull model. Compared with citric acid-supplemented sugarcane juice, UPEC exhibited higher heat resistance in sugarcane juice. Validation of the developed models at 60 °C resulted in satisfactory predictive performance, and the processing times required to achieve 5–7 log reductions were estimated to provide practical guidance for juice safety interventions.

Taken together, this study provides the first integrated evidence of both the local microbial sampling data and exposure risk of UPEC in sugarcane juice retailed in Taiwan, with the development of the predictive inactivation model, highlighting the importance of effective thermal inactivation and improved retail practices. These findings provide scientific evidence to inform microbial risk management strategies for unpasteurized fruit juices and improve public health against emerging foodborne UPEC infections.