Department of Animal Science, University of Wyoming, Laramie, WY 82071, USA.
Int J Food Microbiol. 2012 Oct 15;159(3):186-92. doi: 10.1016/j.ijfoodmicro.2012.09.007. Epub 2012 Sep 19.
Escherichia coli (E. coli) O157:H7 remains a major food safety concern associated with meat, especially beef products. Shiga toxins (Stx) are key virulence factors produced by E. coli O157:H7 that are responsible for hemorrhagic colitis and Hemolytic Uremic Syndrome. Stx are heat stable and can be absorbed after oral ingestion. Despite the extensive study of E. coli O157:H7 survival during meat processing, little attention is paid to the production of Stx during meat processing. The objective of this study was to elucidate the effect of salt, an essential additive to processed meat, at concentrations relevant to meat processing (0%, 1%, 2%, 3%, W/V) on Stx2 production and Stx2 prophage induction by E. coli O157:H7 strains. For both E. coli O157:H7 86-24 and EDL933 strains, including 2% salt in LB broth decreased (P<0.05) E. coli O157:H7 population, but increased (P<0.05) Stx2 production (as measured relative to Log(10)CFU) compared to that of the control (1% salt). Supplementing 3% salt decreased (P<0.05) both E. coli O157:H7 number and Stx2 production. Quantitative RT-PCR indicated that stx2 mRNA expression in culture media containing 2% salt was greatly increased (P<0.05) compared to other salt concentrations. Consistent with enhanced Stx2 production and stx2 expression, the 2% salt group had highest lambdoid phage titer and stx2 prophage induction among all salt treatments. RecA is a key mediator of bacterial response to stress, which mediates prophage activation. Quantitative RT-PCR further indicated that recA mRNA expression was higher in both 2% and 3% salt than that of 0% and 1% salt treatments, indicating that stress was involved in enhanced Stx2 production. In conclusion, salt at the concentration used for meat processing enhances Stx production, a process linked to bacterial stress response and lambdoid prophage induction.
大肠杆菌（E. coli）O157:H7 仍然是与肉类相关的主要食品安全问题，尤其是牛肉产品。志贺毒素（Stx）是大肠杆菌 O157:H7 产生的关键毒力因子，负责引起出血性结肠炎和溶血性尿毒症综合征。Stx 具有热稳定性，可在口服摄入后被吸收。尽管已经广泛研究了大肠杆菌 O157:H7 在肉类加工过程中的存活情况，但在肉类加工过程中 Stx 的产生却很少受到关注。本研究的目的是阐明盐（加工肉类的必需添加剂）的浓度（0％，1％，2％，3％，W/V）对大肠杆菌 O157:H7 菌株产生 Stx2 和诱导 Stx2 前噬菌体的影响。对于大肠杆菌 O157:H7 86-24 和 EDL933 菌株，与对照相比（1％盐），LB 肉汤中添加 2％盐（P<0.05）降低了大肠杆菌 O157:H7 种群，但增加了（P<0.05）Stx2 的产生（相对于 Log10CFU 测量）。补充 3％盐（P<0.05）均降低了大肠杆菌 O157:H7 数量和 Stx2 的产生。定量 RT-PCR 表明，含 2％盐的培养基中 stx2 mRNA 的表达大大增加（P<0.05）与其他盐浓度相比。与增强的 Stx2 产生和 stx2 表达一致，2％盐组在所有盐处理中具有最高的 lambdoid 噬菌体效价和 stx2 前噬菌体诱导。RecA 是细菌应激反应的关键介导物，可介导前噬菌体的激活。定量 RT-PCR 进一步表明，2％和 3％盐处理中的 recA mRNA 表达均高于 0％和 1％盐处理，表明应激反应参与了增强的 Stx2 产生。总之，用于肉类加工的盐浓度增强了 Stx 的产生，这一过程与细菌应激反应和 lambdoid 前噬菌体诱导有关。
