Escherichia coli O157:H7 had a high degree of acid resistance in the presence of osmolytes (glycerol, glycine or fructose) by altering its lipid membrane composition

Abstract

This study aims to investigate the resistance of E. coli O157:H7 to acetic acid (AA) or malic acid (MA) by adding osmolytes, such as glycerol, glycine, glucose, and fructose, in Luria-Bertani broth without NaCl (LBW/S) or phosphate buffer (PB) stored at 25 °C. In LBW/S, a significantly (p < 0.05) higher D-value of E. coli O157:H7 was observed when treated with AA and 20% glycine (D-value: 1.18–3.44) or 40% glucose (D-value: 1.05–2.52) compared to that of AA alone (D-value: 0.40–0.47). In contrast, the addition of osmolytes (i.e. 3-40% glucose, 3–40% fructose or 20% glycine) to LBW/S acidified by MA significantly decreased D-values of E. coli O157:H7, which was enumerated by using a selective medium. Furthermore, when E. coli O157:H7 was incubated in LBW/S containing AA and osmolytes at 25 °C for 3 d, this bacterium had an increased proportion of C16:0 and C17:0 cyclo (cyclopropane acid) compared to its AA-treated counterparts. Along with the altered shift in membrane phospholipids, the addition of osmolytes into a laboratory medium in the presence of nutritive substrates may increase the resistance of E. coli O157:H7 to AA.