酸适应过程中添加牛至精油和氯化钙对沙门氏菌诱导耐酸及其并发的多重抗逆性的影响

Effect of Addition of Oregano Essential Oil and Calcium Chloride during Acid Adaptation on the Acid Tolerance Response and Concurrent Multiple Stress Resistance of Salmonella

为抑制沙门氏菌(Salmonella)在胴体有机酸喷淋减菌后的酸残留环境下产生适应性耐酸反应(acid tolerance response,ATR)及其并发的多重抗逆性,本实验在沙门氏菌酸适应过程中添加不同亚抑菌浓度牛至精油和氯化钙,通过测定适应前后沙门氏菌在酸、热、高渗及氧化环境下的存活能力,研究精油和氯化钙的添加对ATR的抑制效果,并进一步通过测定处理前后抗逆性基因的相对表达,探究其可能的作用机制。结果表明,加工过程中产生的酸残留环境(pH 5.4)可能会诱导沙门氏菌产生ATR现象并引起耐热的交叉保护作用,提示其存在潜在的食品安全风险。使用pH 3的盐酸处理适应后的菌株2 h后,1/2最小抑菌浓度(minimum inhibitory concentration,MIC)牛至精油和10 mmol/L氯化钙处理的菌落下降数比对照组增加了1.32(lg(CFU/mL)),并且两者具有协同抑制ATR的效果。酸适应过程中牛至精油和氯化钙的添加通过下调基因phoP和rpoS的表达干预双组分系统和全局转录因子的作用,从而抑制ATR的产生。亚抑菌浓度的牛至精油能够抑制酸适应后沙门氏菌耐酸与耐热这一交叉保护作用的产生,但增加了沙门氏菌对高渗环境的抵抗能力,而10 mmol/L氯化钙和亚抑菌浓度牛至精油共同作用能够降低沙门氏菌的耐渗能力。本研究有助于了解牛至精油和氯化钙对沙门氏菌酸适应过程的影响,可为工厂有机酸使用的风险控制提供理论依据。

To inhibit the development of adaptive acid tolerance response(ATR)and concurrent multiple stress resistance in Salmonella induced by the residual acid environment from carcass decontamination by organic acid spraying,the inhibitory effect of the addition of oregano essential oil and calcium chloride at different subinhibitory concentrations during acid adaptation on the ATR of Salmonella was investigated by determining the survival ability of Salmonella in acidic,thermal,hyperosmotic and oxidative environments before and after adaptation,and the possible mechanism was explored by determining the relative expression of stress resistance genes before and after treatments.The results indicated that the residual acid(pH 5.4)generated during carcass processing might induce ATR and heat-resistant cross-protection in Salmonella,suggesting a potential food safety risk.After 2 h treatment with hydrochloric acid at pH 3,the loss of the adapted strain in the 1/2 MIC oregano essential oil and 10 mmol/L CaCl_(2)treatment group increased by 1.32(lg(CFU/mL))compared with the control group,and oregano essential oil combined with CaCl_(2)had a synergistic inhibitory effect on ATR.The addition of oregano essential oil and calcium chloride during acid adaptation down-regulated the expression of the phoP and rpoS genes,which in turn intervened in the two-component system and global transcription factors,thereby suppressing ATR development.Sub-inhibitory concentrations of oregano essential oil inhibited the formation of the acid and heat resistance of acid-adapted Salmonella,but increased the resistance to hyperosmosis,whereas CaCl_(2)at a concentration of 10 mmol/L combined with sub-inhibitory concentrations of oregano essential oil reduced the osmotic resistance.The results of the current study help to understand the effects of essential oil and CaCl_(2)on the acid adaptation process of Salmonella and provide a theoretical basis for risk control for the use of organic acids in the beef industry.