Lin Yawei, Peterson Carolyn, Marks Bradley P, Bergholz Teresa M
Department of Food Science and Human Nutrition, Michigan State University, East Lansing, Michigan, USA.
Department of Biosystems and Agricultural Engineering, Michigan State University, East Lansing, Michigan, USA.
Appl Environ Microbiol. 2025 Apr 23;91(4):e0017725. doi: 10.1128/aem.00177-25. Epub 2025 Mar 31.
Previous studies have shown that using a surface growth method for preparing inoculum impacted pathogen population stability and inactivation kinetics. Here, we quantified the desiccation survival and responses to tempering treatment of and Shiga-toxin producing (STEC) on wheat grain when grown using five different methods: broth, lawn-aerobic, lawn-anaerobic, lawn-acid-adapted, and lawn-low inoculum. Three strains of and STEC each were individually inoculated onto wheat grain, conditioned to 0.45 and stored up to 24 weeks. Pathogen survival curves on grain were different when inoculated with a lawn-grown culture compared to broth-grown. Acid adaptation of STEC led to increased ( < 0.001) tolerance to desiccation, while no change in desiccation tolerance was observed. While most survival curves were better described by the log-linear model, survival of pathogens from broth-grown inoculum was better characterized by the Weibull model. Five-strain cocktails of each species were inoculated onto wheat, stored for 1, 2, 7, 28, and 84 days, followed by tempering for 18 h with three chemical interventions: water (control), 800 ppm chlorine, 5% lactic acid (LA) + 26.6% NaCl and 5% sodium bisulfate (SBS). These treatments led to different ( < 0.001) average reductions of 0.52, 1.04, 1.43, and 1.96 log CFU/g, respectively. The length of storage and inoculum growth method affected ( < 0.001) pathogen survival during tempering. In general, pathogens inoculated on grain survived better during tempering when inoculum was prepared by acid-adapted ≥ lawn-aerobic ≥ low inoculum > lawn-anaerobic = broth.IMPORTANCEOutbreaks linked to wheat flour increased interest in evaluating pathogen survival kinetics. With minimal information on how foodborne pathogens contaminate wheat grain, the "worst-case scenario" should be identified to characterize pathogen survival kinetics on grain and be used to assess the effectiveness of food safety interventions. Using an antimicrobial solution during wheat tempering, an existing unit operation where grain is exposed to water prior to milling into flour can be a cost-effective way to mitigate the risk of foodborne pathogens. The lack of consistent inoculum preparation methods makes it difficult to compare results across studies evaluating tempering treatments. We assessed five different inoculum growth methods to quantify pathogen survival during desiccation and long-term storage and pathogen inactivation efficacy of several existing tempering solutions. In addition, these data provide insights on statistically important parameters to consider for low-moisture food challenge study experimental design, such as inoculum growth, inoculation level, and pathogen adaptation.
以往的研究表明，采用表面生长法制备接种物会影响病原体种群稳定性和失活动力学。在此，我们对使用五种不同方法（肉汤法、好氧平板法、厌氧平板法、酸适应平板法和低接种量平板法）在小麦籽粒上生长的单核细胞增生李斯特菌和产志贺毒素大肠杆菌（STEC）的干燥存活情况及对回温处理的反应进行了量化。将三株单核细胞增生李斯特菌和三株STEC分别接种到小麦籽粒上，调节至0.45的水分含量并储存长达24周。与肉汤培养接种相比，用平板培养物接种时，籽粒上的病原体存活曲线有所不同。STEC的酸适应导致对干燥的耐受性增加（P<0.001），而未观察到单核细胞增生李斯特菌干燥耐受性的变化。虽然大多数存活曲线用对数线性模型能更好地描述，但肉汤培养接种物中的病原体存活情况用威布尔模型能更好地表征。将每种菌的五株菌混合接种到小麦上，储存1、2、7、28和84天，然后用三种化学干预措施进行18小时的回温处理：水（对照）、800 ppm氯、5%乳酸（LA）+26.6%氯化钠和5%硫酸氢钠（SBS）。这些处理分别导致平均减少量不同（P<0.001），分别为0.52、1.04、1.43和1.96 log CFU/g。储存时间和接种物生长方法影响（P<0.001）回温期间病原体的存活。一般来说，当接种物通过酸适应法制备时，接种在籽粒上的病原体在回温期间存活得更好，其次是好氧平板法≥低接种量法>厌氧平板法=肉汤法。
与小麦粉相关的疫情增加了对评估病原体存活动力学的兴趣。由于关于食源性病原体如何污染小麦籽粒的信息极少，应确定“最坏情况”以表征病原体在籽粒上的存活动力学，并用于评估食品安全干预措施的有效性。在小麦回温过程中使用抗菌溶液，这是一种在磨粉前使籽粒接触水的现有单元操作，可能是降低食源性病原体风险的一种经济有效的方法。缺乏一致的接种物制备方法使得难以比较评估回温处理的各项研究结果。我们评估了五种不同的接种物生长方法，以量化干燥和长期储存期间病原体的存活情况以及几种现有回温溶液的病原体灭活效果。此外，这些数据为低水分食品挑战研究实验设计中要考虑的统计学上重要的参数提供了见解，如接种物生长、接种水平和病原体适应性。
