Department of Food and Biotechnology, Korea University, Sejong 30019, Republic of Korea.
Department of Animal Sciences, University of Florida, Florida, FL 32611, USA; Emerging Pathogens Institute, University of Florida, Florida, FL 32611, USA.
Int J Food Microbiol. 2022 Feb 16;363:109505. doi: 10.1016/j.ijfoodmicro.2021.109505. Epub 2021 Dec 22.
Bacillus cereus, a foodborne pathogen, is capable of forming spores and biofilms as methods to withstand environmental stresses. These bacterial structures are an issue for food safety as they aid the bacteria survive heat sterilisation processes of foods and food contact surfaces. This study was conducted to investigate the role of the biofilm structure in providing an extra layer of protection to spores against heat treatments. For this, heat resistance of B. cereus spores in intact biofilms was compared to that of planktonic spores in vitro and in a Cheonggukjang jjigae food model. Using methods developed in this study to measure the wet and dry heat resistance of spores in intact biofilms, it was found that B. cereus spores have significantly higher heat resistances when present in biofilms rather than as planktonic spores, and that dry heat is less effective than wet heat at killing spores in biofilms. In further detail, for wet heat treatments, spores in biofilms of the strain isolated from Cheonggukjang (Korean fermented whole soybean), B. cereus CH3, had generally higher wet heat resistances than the reference strain, B. cereus ATCC 10987, both in vitro and in the Cheonggukjang jjigae food model. However, the spores in biofilms of the two strains showed similar heat resistance to dry heat, with some exceptions, when biofilms were formed in vitro or in Cheonggukjang jjigae broth. Meanwhile, B. cereus ATCC 10987 spores in biofilms had higher or similar wet heat resistances in vitro compared to in Cheonggukjang jjigae broth. Wet heat resistances of B. cereus CH3 spores in biofilms were all statistically similar regardless of biofilm formation media (brain heart infusion and Cheonggukjang jjigae broths). For dry heat, spores in biofilms of both B. cereus strains were more heat resistant when biofilms were formed in the Cheonggukjang jjigae food model rather than in vitro. Altogether, heat resistances of spores in biofilms formed in vitro and in the food environment were found to be different depending on the tested B. cereus strain, but higher than planktonic spores in any case. This is the first study examining the heat resistance of B. cereus spores in intact biofilms matrices attached to the surface, both in vitro and in a food model. Therefore, this research is valuable to understand the protective effects of biofilms formed in food environments and to reduce the food safety risks associated with B. cereus.
蜡样芽胞杆菌是一种食源性致病菌，能够形成孢子和生物膜，以此来抵抗环境压力。这些细菌结构是食品安全的一个问题，因为它们帮助细菌在食品和食品接触表面的热灭菌过程中存活下来。本研究旨在调查生物膜结构在为孢子提供额外的热保护方面的作用。为此，比较了完整生物膜中蜡样芽胞杆菌孢子的耐热性与浮游孢子在体外和在朝鲜传统发酵大豆食品模型中的耐热性。使用本研究中开发的方法来测量完整生物膜中孢子的湿热和干热抗性，发现当存在于生物膜中时，蜡样芽胞杆菌孢子比浮游孢子具有更高的耐热性，并且干热在杀死生物膜中的孢子方面不如湿热有效。更详细地说，对于湿热处理，从朝鲜传统发酵大豆（韩国发酵全大豆）中分离出的菌株（CH3）的生物膜中的孢子，其在体外和在朝鲜传统发酵大豆食品模型中的湿热抗性通常高于参考菌株（ATCC 10987）。然而，当在体外或在朝鲜传统发酵大豆汤中形成生物膜时，两种菌株的生物膜中的孢子对干热的耐热性相似，有一些例外情况。同时，与在朝鲜传统发酵大豆汤中相比，ATCC 10987 孢子在生物膜中的湿热抗性在体外更高或相似。无论生物膜形成介质（脑心浸液和朝鲜传统发酵大豆汤）如何，CH3 孢子在生物膜中的湿热抗性在统计学上均相似。对于干热，当生物膜在朝鲜传统发酵大豆食品模型中形成时，两种蜡样芽胞杆菌菌株的生物膜中的孢子更耐热，而不是在体外。总之，体外和食品环境中形成的生物膜中的孢子的耐热性取决于测试的蜡样芽胞杆菌菌株，但无论哪种情况，都高于浮游孢子。这是首次研究在体外和食品模型中研究附着在表面的完整生物膜基质中蜡样芽胞杆菌孢子的耐热性。因此，这项研究对于了解食品环境中形成的生物膜的保护作用以及降低与蜡样芽胞杆菌相关的食品安全风险具有重要意义。
