Survivability of Klebsiella aerogenes on Shell Egg Surfaces During Refrigerated Storage

It is important to understand the survivability of microorganisms on egg surfaces for egg safety and for inoculation studies in antimicrobial investigations. It is also necessary to understand the coverage of cuticle (outermost protective layer) after preparing/treating eggs for inoculation study, as the cuticle may provide antimicrobial properties. A damaged cuticle can increase the risk of bacterial penetration inside the egg. In this study, the surface of egg was spot inoculated with nonpathogenic nalidixic acid resistant Klebsiella aerogenes B 199A on farm fresh egg (control) and after two treatments: eggs washed with tap water at 40 - 46 °C for 15 s and eggs washed with tap water at 40 - 46 °C for 15 s followed by soaking in ethanol for 60 s. The control and treated eggs were stored at 4 °C for 1 h, 24 h, and 48 h. No significant differences were found in K. aerogenes recovery (5.2 - 6.1 log cfu/egg) between all the treatments and control. The non-inoculated treated and control eggs also showed no significant difference from each other for cuticle coverage analyzed after each treatment using dye staining method. Our study showed that the attachment of bacteria on the surface of shell eggs was not affected by different treatments, and the cuticle may not have provided the antimicrobial properties to inactivate K. aerogenes. These results are useful for researchers in egg safety to determine post-inoculation attachment conditions. The data from this study can also be used in predictive growth models like ComBase.

探究微生物在鸡蛋表面的存活情况，对于保障鸡蛋安全以及开展抗菌研究中的接种实验均具有重要意义。同时，在为开展接种实验制备或处理鸡蛋后，明确其角质层（cuticle，最外层保护结构）的覆盖程度同样至关重要，因为该角质层可发挥抗菌特性。受损的角质层会提升细菌侵入鸡蛋内部的风险。本研究以农场新鲜鸡蛋作为对照组，采用无致病性、耐萘啶酸（nalidixic acid）的产气克雷伯菌（Klebsiella aerogenes）B 199A对其表面进行点接种；同时设置两组处理组：其一为将鸡蛋置于40~46℃的自来水下冲洗15秒，其二为先以40~46℃的自来水冲洗15秒，随后将鸡蛋浸入乙醇中浸泡60秒。将对照组与处理组鸡蛋均置于4℃环境下分别储存1小时、24小时及48小时。各组处理组与对照组的产气克雷伯菌回收率（5.2~6.1 log CFU/枚鸡蛋）均无显著差异。采用染料染色法对各处理后的鸡蛋进行角质层覆盖度分析，结果显示未接种的处理组与对照组鸡蛋的角质层覆盖度亦无显著差异。本研究结果表明，不同处理方式未对壳蛋表面的细菌附着情况产生影响，且该角质层可能并未具备灭活产气克雷伯菌的抗菌活性。本研究结果可为鸡蛋安全领域的研究者确定接种后细菌附着条件提供参考依据。本研究产生的数据还可应用于ComBase等微生物生长预测模型中。