Catania Angela Maria, Civera Tiziana, Di Ciccio Pierluigi Aldo, Grassi Maria Ausilia, Morra Patrizia, Dalmasso Alessandra
Department of Veterinary Sciences, University of Turin, Largo Braccini 2, Grugliasco, 10095 Turin, Italy.
Foods. 2021 Nov 21;10(11):2876. doi: 10.3390/foods10112876.
Processed cheese is a commercial product characterized by high microbiological stability and extended shelf life obtained through the application of severe heat treatment. However, spore-forming bacteria can survive through thermal processes. Among them, microorganisms belonging to genus have been reported. In this study, we examined the microbiological population of the first hours' production of processed cheeses in an Italian dairy plant during two seasons, between June and October 2020. Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) was used to identify bacteria colonies, allowing the isolation of and strains. These results were further confirmed by amplification and sequencing of 16 rRNA bacterial region. A multi-locus sequence type (MLST) analysis was performed to assess the genetic similarity among a selection of isolates. The fourteen strains showed two sequence types: ST-32 was observed in only one strain and the ST-371 in the remaining thirteen isolates. On the contrary, all twenty-one strains, included in the study, showed a new allelic profile for the gene, resulting in a new sequence type: ST-249. For strains, analysis of toxin genes was performed. All isolates were positive for , , and , while , , and were not detected. Moreover, the biofilm-forming ability of and strains was assessed, and all selected isolates proved to be biofilm formers (most of them were stronger producers). Considering the genetical similarity between isolates, jointly with the capacity to produce biofilm, the presence of a recurring population could be hypothesized.
加工奶酪是一种商业产品，其特点是通过严格的热处理获得高微生物稳定性和延长的保质期。然而，形成孢子的细菌可以在热加工过程中存活下来。其中，已经报道了属于该属的微生物。在本研究中，我们在2020年6月至10月的两个季节里，对意大利一家乳制品厂加工奶酪生产最初几小时的微生物群落进行了检测。使用基质辅助激光解吸电离飞行时间质谱（MALDI-TOF MS）来鉴定细菌菌落，从而分离出 和 菌株。通过对16 rRNA细菌区域的扩增和测序进一步证实了这些结果。进行多位点序列分型（MLST）分析以评估所选分离株之间的遗传相似性。这14株 菌株显示出两种序列类型：仅在一株中观察到ST-32，其余13株分离株中观察到ST-371。相反，纳入研究的所有21株 菌株，对于 基因显示出一种新的等位基因谱，产生了一种新的序列类型：ST-249。对于 菌株，进行了毒素基因分析。所有分离株 、 和 均呈阳性，而未检测到 、 和 。此外，评估了 和 菌株的生物膜形成能力，所有选定的分离株都被证明是生物膜形成菌（其中大多数是较强的生产者）。考虑到分离株之间的遗传相似性，以及产生生物膜的能力，可以推测存在一个反复出现的 种群。
