Center for Food Safety, College of Agricultural and Environmental Sciences, University of Georgia, Griffin, Georgia 30223.
Department of Food Science & Technology, University of Georgia, Athens, Georgia 30602, USA.
J Food Prot. 2022 Nov 1;85(11):1614-1624. doi: 10.4315/JFP-22-042.
The effect of variations in temperature, UV radiation, and sunlight intensity on Escherichia coli, E. coli O157:H7, Salmonella Newport, and antibiotic resistant (ABR) variants of E. coli O157:H7 and Salmonella Newport exposed to sunlight was evaluated. Bacterial strains suspended in sterile deionized water at a concentration of 8 log CFU/mL were exposed to sunlight on three different days for 180 min; control treatments were stored in the dark. The mean temperature of 30.08 and 26.57°C on day 1 and day 3, respectively, was significantly different (P < 0.05). The UV intensity was significantly different on all 3 days, and sunlight intensity significantly differed on day 3 (P < 0.05). Bacterial population decline positively correlated with temperature, sunlight, and UV intensity. Differences in bacterial population declines differed among species, ABR profile, and day of exposure (P < 0.05). On day 1 and day 2, the populations of E. coli dropped below the limit of detection (1 log CFU/mL), whereas the percentage of live cells was 67 and 6.6%, respectively. The artificial neural network model developed to predict bacterial survival under different environmental conditions suggested that Salmonella cells were more resistant than E. coli cells. The ABR strains had significantly higher numbers of viable cells after sunlight exposure (P < 0.05). Sunlight-exposed cells resuscitated in tryptic soy broth varied in maximum population density and maximum specific growth rate based on bacterial species and presence of ABR. Morphological changes such as viable but nonculturable state transition and filament formation were detected in subpopulations of sunlight-exposed bacteria. Daily fluctuations in UV and sunlight intensity can result in significant variations in bacterial decline and recovery.
本研究评估了温度、紫外线辐射和阳光强度变化对大肠杆菌、O157:H7 型大肠杆菌、沙门氏菌纽波特和暴露于阳光的 O157:H7 和沙门氏菌抗抗生素（ABR）变异体的影响。将浓度为 8 对数 CFU/mL 的无菌去离子水中的细菌悬浮液在三种不同的日子里暴露在阳光下 180 分钟；对照组则储存在黑暗中。第一天和第三天的平均温度分别为 30.08°C 和 26.57°C，差异显著（P<0.05）。所有三天的紫外线强度差异显著，第三天的阳光强度差异显著（P<0.05）。细菌数量的减少与温度、阳光和紫外线强度呈正相关。不同物种、ABR 特征和暴露天数之间的细菌数量减少差异显著（P<0.05）。在第一天和第二天，大肠杆菌的数量降至检测限以下（1 对数 CFU/mL），而活细胞的百分比分别为 67%和 6.6%。为预测不同环境条件下细菌的存活情况而开发的人工神经网络模型表明，沙门氏菌比大肠杆菌更具抵抗力。暴露于阳光后，ABR 菌株的活菌数显著增加（P<0.05）。暴露于阳光的细胞在胰蛋白酶大豆肉汤中复苏，其最大种群密度和最大比生长速率因细菌种类和 ABR 的存在而有所不同。在暴露于阳光的细菌的亚群中检测到了存活但不可培养状态的转变和丝状形成等形态变化。紫外线和阳光强度的日常波动会导致细菌减少和恢复的显著变化。
