Heat Adaptation Improved Cell Viability of Probiotic Enterococcus faecium HL7 upon Various Environmental Stresses

Abstract

The production of viable functional probiotics presupposes stability of strain features in the final product. In previous studies, Enterococcus faecium HL7 was found to have relatively higher cell viability after freeze-drying and the long-lasting resistance to heat (60 °C) as well as higher antimicrobial activities against some of fish and human pathogens among isolated strains. For heat adaptation, E. faecium HL7 cells were exposed to 52 °C for 15 min. After adaption, slight decreases of unsaturated membrane fatty acid ratios were confirmed through fatty acid analysis. Upon subsequent exposure to various stress conditions such as HO (0.01%), ethanol (20%), acid (pH 3), and alkali (pH 12), the survival rate of heat-adapted HL7 was 10-10-fold higher than that of non-adapted one. These results highlight the potential of preconditioning treatments for maximizing survival of probiotic bacteria during development of probiotic functional foods. The cross-protection afforded by acid against thermal stress may indicate that certain common protective mechanisms are induced by both heat and acid stress. These results can be applied to enhancing the cell viability during live cell formulation of E. faecium HL7 to be used as a potential probiotics in aquaculture.

Adaptive changes in saturated fatty acids as a resistant mechanism in salt stress in Halomonas alkaliphila YHSA35

“…These agree with those obtained by several workers. Wherever they investigated that the microbial growth under biotic and/or abiotic stress has a direct influence in saturated and unsaturated fatty acids degree among the membrane (Sullivan et al, 1979;Arneborg et al, 1993;Rozes &Peres, 1998 andShin et al, 2018). Many authors reported that an increase in fatty acids saturation degree afterwards decrease the membrane fluidity (Keweloh et al, 1991;Weber &de Bont, 1996 andFakhruddin &Quilty, 2006).…”

The Inoculation of Probiotics In Vivo Is a Challenge: Strategies to Improve Their Survival, to Avoid Unpleasant Changes, or to Enhance Their Performances in Beverages

“…Another kind of pretreatment is heat adaptation based on microbial exposure to sublethal temperatures (for example, 52 • C for 15 min) [36]; this pretreatment can increase resistance to low or alkaline pHs, ROS, ethanol, spray-drying, etc.…”

Adaptive laboratory evolution of heat tolerance in Streptococcus thermophilus BIOPOP-1 and BIOPOP-2 under gradually increasing heat temperature

“…Prolonged heat treatment at constant temperature Prior to the experiment, both WT and ALE strains were adapted at sub-lethal temperature, 52°C for 15 min. Studies showed that heat adapted LABs have higher viability ratio compared to non-adapted ones [15]. Microorganisms defined their heat tolerance by D value (decimal reduction time) which is exposure time required to causes one log 10 or 90% reduction of the initial population under specified temperature [16].…”

“…The fatty acid composition and the ability of the cells to resist the above mentioned stresses are closely related. Many researches have shown that lowering concentration of unsaturated fatty acids (UFAs) or increasing concentration of saturated fatty acids (SFAs) is decreased membrane fluidity and related to higher heat tolerance [15,21,22]. S. thermophilus BIOPOP-1 (WT)'s membrane is made of seven fatty acids and that of ALE strain consists of eight fatty acids.…”

“…Also, membrane of BIOPOP-2 (WT) is made of six fatty acids and that of ALE strain is composed of seven fatty acids. They were divided into two groups: saturated fatty acids and unsaturated fatty acids [15]. The fatty acid compositions for all WT and ALE strains are summarized details in Table 2.…”