Dipartimento di Scienze Agrarie, Alimentari ed Ambientali, Università Politecnica delle Marche, via Brecce Bianche, 60131 Ancona, Italy.
Department of Agricultural, Forest, and Food Science, University of Turin, Largo Paolo Braccini 2, Grugliasco, Torino, Italy.
Food Res Int. 2022 Dec;162(Pt B):112083. doi: 10.1016/j.foodres.2022.112083. Epub 2022 Oct 28.
The present research reports the results of a long-term study (70 days) of the dynamics of Staphylococcus aureus artificially inoculated in a Tenebrio molitor rearing chain for human consumption. To this end, a rearing substrate consisting of organic wheat middlings was spiked with S. aureus to obtain three initial contamination levels, namely 1 (low level), 5 (medium level) and 7 (high level) Log colony forming unit per gram. Microbial viable counting coupled with metataxonomic analysis were performed to evaluate: i) the persistence and growth of S. aureus in the rearing substrate; ii) the colonization and growth of S. aureus in the insect larvae; iii) the occurrence and load of S. aureus in the frass (excrement from larvae mixed with substrate residues); iv) the presence of S. aureus enterotoxins in the rearing substrate, frass, and larvae. The results of the present study highlighted that wheat middlings contaminated with S. aureus do not represent a suitable environment for the multiplication of the pathogen, irrespective of the initial contamination level. Of note, frass originated from the larvae reared on contaminated wheat middlings might potentially represent a source of S. aureus, with cell loads depending on the initial contamination level. A complex resident microbiota was revealed by metataxonomic analysis. Interestingly, co-occurrence/co-exclusions analysis did not reveal associations between the target microorganism and the microbiota of wheat middlings, larvae, or frass. Considering safety aspects of larvae, the results overall collected suggested that, under the applied conditions, T. molitor represents an inhospitable or even hostile environment for S. aureus, with this latter showing counts below the detection limit in the larvae at the end of the 70-day rearing trial, irrespective of the initial contamination level. The results also suggested that a combination of bactericidal factors, including unfavorable environmental conditions (such as low a of wheat middlings and frass), might have established in the rearing chain. Finally, the absence of staphylococcal toxins suggests that, even when S. aureus is present at high contamination levels, it is not able to produce toxins in wheat middlings, larvae, or frass.
本研究报告了一项为期 70 天的人工接种金黄色葡萄球菌在用于人类消费的黄粉虫饲养链中的动态的长期研究结果。为此，用金黄色葡萄球菌对由有机小麦次粉组成的饲养基质进行了接种，以获得三个初始污染水平，即 1（低水平）、5（中水平）和 7（高水平）每克菌落形成单位。进行了微生物活菌计数和分类组学分析，以评估：i）金黄色葡萄球菌在饲养基质中的存活和生长；ii）金黄色葡萄球菌在昆虫幼虫中的定植和生长；iii）在虫粪（幼虫与基质残渣混合的粪便）中金黄色葡萄球菌的出现和负荷；iv）在饲养基质、虫粪和幼虫中金黄色葡萄球菌肠毒素的存在。本研究的结果表明，无论初始污染水平如何，用金黄色葡萄球菌污染的小麦次粉都不能为病原体的繁殖提供合适的环境。值得注意的是，由饲养在受污染的小麦次粉上的幼虫产生的虫粪可能潜在地成为金黄色葡萄球菌的来源，其细胞负荷取决于初始污染水平。分类组学分析揭示了复杂的驻留微生物群。有趣的是，共现/排除分析并未发现目标微生物与小麦次粉、幼虫或虫粪的微生物群之间存在关联。考虑到幼虫的安全性，总体而言，研究结果表明，在应用条件下，黄粉虫对金黄色葡萄球菌来说是一个不适宜甚至敌对的环境，在 70 天的饲养试验结束时，无论初始污染水平如何，金黄色葡萄球菌的计数均低于检测限。研究结果还表明，在饲养链中可能建立了包括不利环境条件（如小麦次粉和虫粪的低 a 值）在内的杀菌因子的组合。最后，没有金黄色葡萄球菌毒素表明，即使金黄色葡萄球菌的污染水平很高，它也不能在小麦次粉、幼虫或虫粪中产生毒素。
