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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
Author(s) -
Samelis J.,
Ikeda J.S.,
Sofos J.N.
Publication year - 2003
Publication title -
journal of applied microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.889
H-Index - 156
eISSN - 1365-2672
pISSN - 1364-5072
DOI - 10.1046/j.1365-2672.2003.02013.x
Subject(s) - listeria monocytogenes , salmonella , escherichia coli , library science , microbiology and biotechnology , biology , bacteria , computer science , genetics , gene
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 3·5 or 3·7 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 0·2 unit difference in challenge pH (3·5–3·7) 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 acid‐adapted 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 stationary‐phase ATR of L. monocytogenes and S . Typhimurium DT104, but their effect on ATR of E. coli O157:H7 appears to be far less dramatic.