Evaluation of the pH-dependent, stationary-phase acid tolerance in Listeria monocytogenes and Salmonella Typhimurium DT104 induced by culturing in media with 1% glucose: a comparative study with Escherichia coli O157:H7

Abstract

Aims: To comparatively evaluate the adaptive stationary-phase acid tolerance response (ATR) in food-borne pathogens induced by culturing in glucose-containing media, as affected by strain variability and antibiotic resistance, growth temperature, challenge pH and type of acidulant. Methods and Results: Antibiotic resistant or sensitive strains of Listeria monocytogenes, Salmonella including S. Typhimurium DT104, and Escherichia coli O157:H7 were cultured (30°C for 24 h; 10°C for up to 14 days) in trypticase soya broth with yeast extract (TSBYE) with 1% or without glucose to induce or prevent acid adaptation, respectively. Cultures were subsequently exposed to pH 3AE5 or 3AE7 with lactic or acetic acid at 25°C for 120 min. Acid-adapted cultures were more acid tolerant than nonadapted cultures, particularly those of L. monocytogenes and Salmonella. No consistent, positive or negative, influence of antibiotic resistance on the pH-inducible ATR or acid resistance (AR) was observed. Compared with 30°C cultures, growth and acid adaptation of L. monocytogenes and S. Typhimurium DT104 at 10°C markedly reduced their ATR and AR in stationary phase. E. coli O157:H7 had the greatest AR, relying less on acid adaptation. A 0AE2 unit difference in challenge pH (3AE5-3AE7) caused great variations in survival of acid-adapted and nonadapted cells. Conclusions: Culturing L. monocytogenes and Salmonella to stationary phase in media with 1% glucose induces a pH-dependent ATR and enhances their survival to organic acids; thus, this method is suitable for producing acidadapted cultures for use in food challenge studies. Significance and Impact of the Study: Bacterial pathogens may become acid-adapted in foods containing glucose or other fermentable carbohydrates. Low storage temperatures may substantially decrease the stationaryphase ATR of L. monocytogenes and S. Typhimurium DT104, but their effect on ATR of E. coli O157:H7 appears to be far less dramatic.

Survival or Growth of Escherichia coli O157:H7 in a Model System of Fresh Meat Decontamination Runoff Waste Fluids and Its Resistance to Subsequent Lactic Acid Stress

“…In acetic acid washings stored at 4°C, most of the colonies grown on TSAYE plates (Table 2) were surviving cells of E. coli O157: H7, since yeasts and lactic acid bacteria did not increase under refrigeration. In sterile meat washings and saline, populations on TSAYE (data not shown) were similar to those on TSAYEϩrif ( Table 1), confirming that rifampin did not affect the behavior of strain ATCC 43895rifϩ (36).…”

“…A rifampin-resistant (Rif ϩ ) (100 g/ml) derivative of the meat outbreak E. coli O157:H7 strain ATCC 43895 was used. This strain was selected for use in the present and previous (33,34,35,37) meat decontamination studies because of its high inherent acid resistance (5, 6); it was ensured that the Rif ϩ derivative showed an acid resistance as high as that of its parental strain (36). The strain was activated by two consecutive transfers (30°C, 24 h) in 10 ml of Trypticase soy broth (BBL, Becton Dickinson Co., Sparks, MD) with 0.6% yeast extract (Difco, Becton Dickinson Co., Sparks, MD) (TSBYE).…”

“…The strain was activated by two consecutive transfers (30°C, 24 h) in 10 ml of Trypticase soy broth (BBL, Becton Dickinson Co., Sparks, MD) with 0.6% yeast extract (Difco, Becton Dickinson Co., Sparks, MD) (TSBYE). Non-acid-adapted and acid-adapted inocula were prepared by transferring 0.1 ml of the activated culture in 10 ml of glucose-free TSBYE (BBL) or glucose-free TSBYE with 1% added glucose (Sigma, St. Louis, MO), respectively, as described previously (35,36). After 24 h of incubation at 30°C, the pH of the acid-adapted cultures was 5.0 Ϯ 0.1 while the pH of nonadapted cultures was 6.8 Ϯ 0.1.…”

“…Acetic acid was not used as an acidulant in this study because previous studies have shown rapid declines below the detection limit of E. coli O157:H7 when it is exposed to pH 3.5 with this acid (30,36). Specifically, a 0.2-unit difference in challenge pH (3.5 to 3.7) of TSBYE acidified with acetic acid caused great variations in survival of acid-adapted and nonadapted cells of strain ATCC 43895 (36). This suggests that reliability and reproducibility of acid challenge tests may be reduced as a result of slight differences in the pH or the volume of acetic acid added.…”

Transcriptomic and Phenotypic Responses of Listeria monocytogenes Strains Possessing Different Growth Efficiencies under Acidic Conditions

“…To accelerate the processing time and maintain acceptable flavors, meat products are often dipped into lactate and acetate mixtures. There is a possibility that transient exposures to organic acids may contribute to survival and potential persistence of L. monocytogenes strains in factory environments by selecting for acid-resistant strains (39,56,62).…”