Salad dressing spoilage by Bacillus amyloliquefaciens with gas formation

Abstract B. amyloliquefaciens is a Gram-positive, aerobic, motile rod, often found in soil, which has been described as a plant growth promoter and is used in several industrial processes. This study reports an episode involving the gassy spoilage of salad dressing caused by B. amyloliquefaciens in a production facility located in Rio de Janeiro, Brazil. Nine B. amyloliquefaciens strains were isolated from spoiled salad dressings, the sugar used as a raw material in the manufacture and from the production plant. A genotypic analysis of the isolates by Rep-PCR generated eight band profiles grouped in five Rep-PCR clusters. When re-inoculated into fresh salad dressing three B. amyloliquefaciens isolates belonging to the Rep-PCR clusters A, D and E were able to reproduce the gassy spoilage process, whereas the isolates belonging to the Rep-PCR clusters B and C did not produce any visible spoilage, suggesting that these isolates were not directly involved in the spoilage process. The predominant Rep-PCR cluster, cluster A, included strains isolated from barbecue and passion fruit seed salad dressings and from sugar (raw material), suggesting it is a common source of contamination for such salad dressings.摘要：解淀粉芽孢杆菌（B. amyloliquefaciens）是一类革兰氏阳性、需氧且具有运动性的杆状细菌，广泛存在于土壤中，被证实可作为植物生长促生剂，并已应用于多项工业生产流程。本研究报道了一起发生在巴西里约热内卢某生产设施内，由解淀粉芽孢杆菌引发的沙拉酱产气变质事件。研究人员从变质沙拉酱、生产所用原料糖以及生产设施中分离得到9株解淀粉芽孢杆菌分离株。通过重复基因外回文序列PCR（Rep-PCR）对分离株进行基因型分析，共获得8条条带图谱，可划分为5个Rep-PCR聚类簇。将属于聚类簇A、D、E的3株解淀粉芽孢杆菌分离株重新接种至新鲜沙拉酱中，可成功重现产气变质过程；而属于聚类簇B和C的分离株未引发任何可见变质现象，提示此类分离株并未直接参与本次变质事件。占主导地位的Rep-PCR聚类簇A涵盖了分离自烧烤酱、西番莲籽沙拉酱及原料糖的菌株，表明该聚类簇是此类沙拉酱的常见污染来源。