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.

探究微生物在蛋壳表面的存活情况，对于鸡蛋安全防控以及抗菌研究中的接种实验均具有重要意义。此外，在为接种实验制备或处理鸡蛋后，还需明确其角质层（cuticle）的覆盖情况——该结构作为蛋壳最外层的保护性屏障，可发挥抗菌防护作用；若角质层受损，则会提升细菌侵入蛋内的风险。本研究以农场新鲜鸡蛋为实验材料，设置未处理对照组与两种预处理组：采用非致病性耐萘啶酸产气克雷伯菌（Klebsiella aerogenes）B 199A对各组蛋壳表面进行点接种处理。两种预处理方案分别为：方案一，用40~46℃自来水冲洗鸡蛋15秒；方案二，先用40~46℃自来水冲洗15秒，再经乙醇浸泡60秒。将对照组与预处理组的鸡蛋置于4℃环境下，分别储存1小时、24小时及48小时。各组预处理组与对照组的产气克雷伯菌回收率（5.2~6.1 log CFU/枚蛋）均无显著差异。采用染料染色法对各处理组及对照组的未接菌鸡蛋进行角质层覆盖度检测，结果显示两组间同样无显著差异。本研究结果表明，不同预处理方式不会改变细菌在蛋壳表面的附着情况，且该角质层可能并未发挥灭活产气克雷伯菌的抗菌作用。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，同时相关数据还可应用于ComBase等微生物预测生长模型中。