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Thermotolerance of Rifampicin‐Resistant E scherichia coli O 157: H 7 Derivatives and Their Parental Strains in a Broth System
Author(s) -
Ko Kyung Yuk,
Geornaras Ifigenia,
Byelashov Oleksandr A.,
Paik HyunDong,
Kim KeeTae,
Sofos John N.
Publication year - 2016
Publication title -
journal of food safety
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.427
H-Index - 43
eISSN - 1745-4565
pISSN - 0149-6085
DOI - 10.1111/jfs.12207
Subject(s) - rifampicin , microbiology and biotechnology , escherichia coli , tryptic soy broth , strain (injury) , agar , chemistry , biology , bacteria , food science , antibiotics , gene , biochemistry , genetics , anatomy
Rifampicin‐resistant ( Rif R ) strains have often been used in studies of E scherichia coli O 157: H 7 to assure more specific recovery. The present study compared the heat inactivation kinetics of rifampicin‐resistant variants of pathogenic and nonpathogenic E . coli O 157 strains with those of the wild‐type parental strains. Spontaneous Rif R derivatives of 11 pathogenic and six nonpathogenic E . coli O 157 strains were selected. Stationary‐phase cells of each strain in sterile tryptic soy broth were heated at 60 C for 0, 30, 60, 90, 120, 150, 180 or 240 s, and aliquots were plated on tryptic soy agar supplemented with 0.1% pyruvate + 100 μg/mL rifampicin. D values of three pathogenic and two nonpathogenic Rif R E . coli O 157 strains were 35–70% lower ( P < 0.05) than those of their wild‐type counterparts. However, the heat resistance of most of the Rif R E . coli O 157: H 7 strains (12 strains) was similar ( P ≥ 0.05) to that of their parental counterparts. Therefore, the findings of this study demonstrated that the majority of the rifampicin‐resistant E. coli O157:H7 variants that were evaluated to assure more reliable recovery in microbial inactivation studies are suitable for use in various heat challenge studies.Practical Applications More reliable media are needed for the isolation or recovery of E . coli O 157: H 7 in inoculated challenge studies. Prior to use of rifampicin‐resistant E . coli O 157: H 7 strains in heat challenge studies, it is important that their thermal inactivation kinetics be compared with those of their wild‐type parental strains. The results of this study showed that the thermotolerance at 60 C of the majority of the tested rifampicin‐resistant E . coli O 157: H 7 variants was not different than that of the corresponding wild‐type strains. These rifampicin‐resistant strains can, therefore, be used in heat challenge studies and can be recovered with non‐selective culture media supplemented with rifampicin.