Zhang Guodong, Ma Li, Patel Nehal, Swaminathan Bala, Wedel Stephanie, Doyle Michael P
Center for Food Safety, University of Georgia, 1109 Experiment Street, Griffin, Georgia 30223, USA.
J Food Prot. 2007 Apr;70(4):997-1001. doi: 10.4315/0362-028x-70.4.997.
During May and June of 2005, 26 persons in several states were infected by a single strain (isolates indistinguishable by pulsed-field gel electrophoresis) of Salmonella enterica serotype Typhimurium after eating cake batter ice cream. The cake mix used to prepare the cake batter in the ice cream was implicated by epidemiologic investigation as the source of Salmonella contamination. Initial tests did not detect Salmonella in cake mix collected during the outbreak investigation. The objective of this study was to evaluate different procedures to isolate Salmonella from the implicated cake mix, cake, and ice cream. All outbreak-associated food samples (14 samples) were collected during the outbreak investigation by health departments of several of the states involved. Different combinations of Salmonella isolation procedures, including sample size, preenrichment broth, enrichment broth, enrichment temperature, and isolation medium, were used. Salmonella Typhimurium was isolated from two cake mix samples; the food isolates were indistinguishable from the outbreak pattern by pulsed-field gel electrophoresis subtyping. Universal preenrichment broth was substantially better than was lactose broth for preenrichment, and tetrathionate broth was better than was Rappaport-Vassiliadis broth for isolating Salmonella from the two positive cake mix samples. Although more typical Salmonella colonies were observed on plates from enrichment cultures grown at 35 degrees C, more confirmed Salmonella isolates were obtained from plates of enrichment cultures grown at 42 degrees C. Brilliant green agar, xylose lysine tergitol 4 agar, xylose lysine desoxycholate agar, Hektoen enteric agar, and bismuth sulfite agar plates were equally effective in isolating Salmonella from cake mix. The best combination of preenrichment-enrichment conditions for isolating the outbreak strain of Salmonella was preenrichment of cake mix samples in universal preenrichment broth at 35 degrees C for 24 h, followed by enrichment in tetrathionate broth at 42 degrees C for 24 h.
2005年5月和6月期间，几个州的26人在食用蛋糕面糊冰淇淋后感染了单一菌株（通过脉冲场凝胶电泳无法区分的分离株）的肠炎沙门氏菌鼠伤寒血清型。用于制作冰淇淋中蛋糕面糊的蛋糕预拌粉经流行病学调查被认为是沙门氏菌污染的源头。在疫情调查期间收集的蛋糕预拌粉初步检测未发现沙门氏菌。本研究的目的是评估从受牵连的蛋糕预拌粉、蛋糕和冰淇淋中分离沙门氏菌的不同程序。所有与疫情相关的食品样本（14个样本）均在疫情调查期间由几个相关州的卫生部门收集。使用了沙门氏菌分离程序的不同组合，包括样本量、预增菌肉汤、增菌肉汤、增菌温度和分离培养基。从两份蛋糕预拌粉样本中分离出了鼠伤寒沙门氏菌；通过脉冲场凝胶电泳亚型分析，食品分离株与疫情模式无法区分。通用预增菌肉汤在预增菌方面明显优于乳糖肉汤，而四硫磺酸盐肉汤在从两份阳性蛋糕预拌粉样本中分离沙门氏菌方面优于Rappaport-Vassiliadis肉汤。虽然在35℃培养的增菌培养平板上观察到更多典型的沙门氏菌菌落，但从42℃培养的增菌培养平板上获得了更多经确认的沙门氏菌分离株。亮绿琼脂、木糖赖氨酸去氧胆酸盐4琼脂、木糖赖氨酸脱氧胆酸盐琼脂、Hektoen肠道琼脂和亚硫酸铋琼脂平板在从蛋糕预拌粉中分离沙门氏菌方面同样有效。分离疫情株沙门氏菌的最佳预增菌-增菌条件组合是将蛋糕预拌粉样本在35℃的通用预增菌肉汤中预增菌24小时，然后在42℃的四硫磺酸盐肉汤中增菌24小时。
