Starvation- and stationary-phase-induced acid tolerance in Escherichia coli O157:H7

Abstract

Stationary phase and the starvation of log-phase cells increased the acid tolerance of Escherichia coli O157:H7 strains. Although the degree of acid tolerance varied, the survival of most O157:H7 strains exceeded that of other, related, pathogens in a synthetic gastric fluid. Escherichia coli O157:H7 is recognized as an important cause of hemorrhagic colitis and hemolytic uremic syndrome that is disseminated by foods, water, and person-to-person contact (13). Although ground beef has been implicated as the primary vehicle of transmission (13), outbreaks of E. coli O157:H7 involving apple cider (2), mayonnaise (27), and yogurt (24) have raised concerns about the safety of high-acid foods and the acid tolerance properties of this pathogen. In addition to epidemiological data, studies of survival in acidic foods (1, 2, 10, 23, 25, 27) demonstrate that E. coli O157:H7 is acid tolerant, particularly at lower temperatures (23, 27). Studies with nonpathogenic E. coli and Salmonella typhimurium demonstrate that prior exposure to acidic conditions or growth in a moderately acidic medium enhances survival at low pH (7, 8, 11). This inducible acid tolerance system promotes survival of S. typhimurium in cheese (20) and is important to the virulence of the organism (9). Recently, two pHdependent systems were described; one is induced in log phase, and the other is induced in stationary phase (7, 19, 26). A third system, which is pH independent, is induced by stationary phase and involves the rpoS gene encoding sigma factor 38 (14, 18, 19, 21, 26). The present study was initiated to identify environmental and physiological factors affecting acid tolerance in E. coli O157:H7 and to compare the acid tolerance of O157:H7 strains with that of other, related, pathogens. Seven strains of E. coli O157:H7 (ATCC 43889, ATCC 43894, ATCC 43895, 84-01, TB 226, TB 285, and JBL 1935); enteroinvasive E. coli serotypes O124 and O152 (10011 and 10010, respectively); enteropathogenic E. coli serotypes O111:H2 and O127:H6 (B170 and E2348169, respectively); a nonpathogenic control strain, E. coli C (Food Research Institute-Kaspar [FRIK] culture collection isolate 123); and Shigella dysenteriae type 1 (ATCC 29026) were used in these studies. Stock cultures were maintained in liquid nitrogen in 10% glycerol. Cultures were grown overnight in Trypticase soy broth (TSB) (BBL Microbiology Systems, Cockeysville, Md.) at 35ЊC with shaking (150 rpm) and transferred to fresh medium on consecutive days at least twice before use in experiments. Cultures in the logarithmic and stationary phases of growth were obtained by monitoring growth at 35ЊC in TSB spectrophotometrically: mid-log phase, A 600 ϭ 0.3 (1.2 h, ca. 1 ϫ 10 8 CFU/ml); late log phase, A 600 ϭ 0.7 (3 h, ca. 3 ϫ 10 8 CFU/ml); and stationary phase, A 600 ϭ 1.1 (7 h, ca. 1 ϫ 10 9 CFU/ml).

Cell density dependent acid sensitivity in stationary phase cultures of enterohemorrhagic Escherichia coli O157:H7

“…At the stationary phase, several bacteria exhibit a higher level of resistance to low pH, high temperature, high osmolarity and oxidative stress than the exponential phase cultures. Results from several laboratories have shown that the acid resistance in E. coli O157:H7 is much higher in the stationary phase than in the exponential phase [8,23]. Similar observations have also been made in Shigella [9], Salmonella [24] and Listeria [25].…”

Influence of prior pH and thermal stresses on thermal tolerance of foodborne pathogens

“…Therefore, decreased heat tolerance may occur due to the reduced melting point of unsaturated fatty acids within the cell membrane. Other scientist have also indicated that the stress response of bacteria to sublethal environmental stresses such as changes in temperature, starvation, or high osmolarity may provide cross-protection to a variety of postphysical and postchemical stresses including heat and acid (Allen, Lepp, McKellar, & Griffiths, 2010;Arnold & Kaspar, 1995;Erdoğrul, Erbilir, & Toroğlu, 2006;House et al, 2009;Jeong, Baumler, & Kaspar, 2006;Lange & Hengge-Aronis, 1994;Leenanon & Drake, 2001;Nair & Finkel, 2004).…”

Improving low water activity and desiccation tolerance of the biocontrol agent Pantoea agglomerans CPA-2 by osmotic treatments

“…have been extensively studied and reported. Initial investigations carried out on bacteria such as Escherichia coli (Arnold and Kaspar 1995;Poirier et al 1998), Salmonella spp. (O'Driscoll et al 1996Mattick et al 2000Mattick et al , 2001 and Listeria spp.…”