Susceptibility to Antibiotics and Reactive Oxygen Species in Escherichia coli: A Survey of Clinical and Environmental Isolates

Aims: Some bacterial responses to oxidative stress also diminish antibiotic susceptibility; also, some antibiotics do increase oxidative stress within bacterial cells. Linkage or cross-resistance to prooxidants and antibiotics could facilitate the selection of antibiotic resistance and/or virulence. We made this survey in order to detect this possible linkage in Escherichia coli isolates.

Methodology: The susceptibility of 102 E. coli clinical (causative of urinary or gastrointestinal infections) and environmental (rural or urban dust) isolates towards paraquat, H2O2, and antibiotics was measured using disc assays. Catalase and superoxide-dismutase (SOD) activities were measured.

Results: Susceptibility to prooxidants was similar across isolates of all four sources, but urinary and urban dust isolates were more resistant to antibiotics. H2O2 "resistant" organisms had more antibiotic resistance phenotypes, particularly towards sulfadiazine and tetracycline. Paraquat "resistance" seems associated to beta-lactam resistance; but paraquat "susceptibility" seems associated to resistance towards chloramphenicol, gentamicin, ciprofloxacin and nitrofurantoin. Prooxidant disc assays correlate to catalase and superoxide-dismutase activities. A weak relationship H2O2/antibiotic-resistance, but not superoxide/antibiotic-resistance, is suggested.

Conclusion: Overall, antibiotics exerting their action through oxidative stress, do not seem to have resulted in the co-selection of oxidative stress resistance, or vice versa. However, a possible link between resistance to some antibiotics and to H2O2 might contribute to co-selection between these two chemical insults.