Sublethal concentrations of undissociated acetic acid may not always stimulate acid resistance in Salmonella enterica sub. enterica serovar Enteritidis Phage Type 4: Implications of challenge substrate associated factors

Abstract

Acid adaptation enhances survival of foodborne pathogens under lethal acid conditions that prevail in several food-related ecosystems. In the present study, the role of undissociated acetic acid in inducing acid resistance of Salmonella Enteritidis Phage Type 4 both in laboratory media and in an acid food matrix was investigated. Several combinations of acetic acid (0, 15, 25, 35 and 45 mM) and pH values (4.0, 4.5, 5.0, 5.5, 6.0) were screened for their ability to activate acid resistance mechanisms of pathogen exposed to pH 2.5 (screening assay). Increased survival was observed when increasing undissociated acetic acid within a range of sublethal concentrations (1.9-5.4 mM), but only at pH 5.5 and 6.0. No effect was observed at lower pH values, regardless of the undissociated acetic acid levels. Three combinations (15mM/pH5.0, 35mM/pH5.5, 45mM/pH6.0) were selected and further used for adaptation prior to inoculation in commercial tarama (fish roe) salad, i.e., an acid spread (pH 4.35 ± 0.02), stored at 5˚C. Surprisingly and contrary to the results of the screening assay, none of the acid adaptation treatments enhanced survival of Salmonella Enteritidis in the food matrix, as compared to non-adapted cells (control). Further examination of the food pH value, acidulant and storage (challenge) temperature on the responses of the pathogen adapted to 15mM/pH5.0, 35mM/pH5.5 and 45mM/pH6.0 was performed in culture media. Cells adapted to 35mM/pH5.5 were unable to induce acid resistance when exposed to pH 4.35 (tarama salad pH value) at 37˚C and 5˚C, whereas incubation under refrigeration (5˚C) at pH 4.35 sensitized 45mM/pH6.0 adapted cells against the subsequent acid and cold stress. In conclusion, pre-exposure to undissociated acetic acid affected the adaptive responses of Salmonella Enteritidis Phage Type 4 in a concentration-and pH-dependent manner, with regard to conditions prevailing during acid challenge.

In Vitro Investigation of the Antibacterial Activity of Nine Commercial Water Disinfectants, Acidifiers, and Glyceride Blends against the Most Important Poultry Zoonotic Bacteria

“…Water sanitation and/or acidification is a promising practice for lowering the use of antibiotics in human and veterinary medicine [ 18 , 19 , 20 ]. However, the existence of knowledge gaps on the antibacterial activity of the commercially available water disinfectants, acidifiers, and glyceride blends, as well as the potential for microbes to develop resistance to these alternative biocides [ 27 , 28 , 29 , 30 ], emphasizes the significance of future research [ 39 ].…”

“…There are many knowledge gaps concerning the ability of bacteria to develop resistance to these alternative antimicrobials [ 27 , 28 , 29 , 30 ]. There is evidence that residual levels of applied acidic blends or disinfectants may trigger adaptation to oxidative stress by genetic mutations and/or horizontal transfer of antimicrobial resistance genes among the exposed bacteria [ 29 , 30 ].…”

Inhibition of Cronobacter sakazakii in an infant simulator of the human intestinal microbial ecosystem using a potential synbiotic

“…For example, Zhang et al (2020) reported that SCFAs in a broth medium with a pH of 6.5 were able to inhibit the growth of E. coli, whereas a neutral pH stimulated its growth. Foodborne pathogens, including C. sakazakii, can develop acid resistance when exposed to sub-lethal concentrations of acetate, although the adaptation is influenced by the acid concentration and the pH of the environment (Arnold et al, 2001;Álvarez-Ordóñez et al, 2012;Gavriil et al, 2020). E. coli can adapt to the acid stress induced by SCFAs at a neutral pH by regulating the expression of rpoS (Arnold et al, 2001).…”