Effect of β-lactam antibiotic resistance gene expression on the radio-resistance profile of O157:H7.

Some pathogens might develop favorable global adaptation in response to certain stress treatments resulting in enhanced virulence and/or resistance to a different stress. β-lactam resistance, as well as and genes involved in this resistance, were studied to evaluate their possible role in O157:H7 () radioresistance. adapted to 25, 15 or 7 μg/mL of kanamycin or carbenicillin, were produced and treated with sensitization (0.4 kGy) or lethal (1.5 kGy) irradiation doses. In O157:H7, irradiation treatment at 0.4 kGy dose increased and expression respectively by 1.6 and 2-fold in the wild type strain (Wt) but up to by 2.4 and 3.4-fold when the strain was beforehand adapted to 25 μg/mL of carbenicillin (Carb25). Accordingly, Δ and Δ mutants and adapted to 25 μg/mL of kanamycin were more sensitive to 0.4 kGy treatment than Wt. While, Carb25 or overexpression of and provided complete resistance to 0.4 kGy and were even able to survive and grow after exposure to a normally lethal 1.5 kGy irradiation dose. We further noticed that these strains can tolerate other stresses like oxidative, cold and heat shocks. This demonstrates that carbenicillin adaptation promotes resistance to γ-irradiation and to other stresses, likely at least through increased AmpC and AmpG expression. These results are important for the food industry and particularly when considering the use of irradiation for food preservation of meat obtained directly from animals fed β-lactam antibiotics.