Sachiko Hayakawa, Emiko Furukawa, Masato Kawamura, Toshiaki Kikuchi, Taizou Hirano, Akira Watanabe and Shigeru Fujimura
Pseudomonas aeruginosa is one of the most common causes of nosocomial infections. Hospital associated infection by multidrug resistant (MDR) strains constitute a serious problem worldwide. The aim of the present study was to evaluate whether exposure to sub-MIC levels of anti-pseudomonas antibiotics and reactive oxygen species (ROS), such as hydroxyl radicals, could lead to MDR of P. aeruginosa. P. aeruginosa standard strain PAO1 was used in this study. All five anti-pseudomonas agents, that is, piperacillin, levofloxacin, meropenem, ceftazidime and amikacin, were investigated for induction of resistance and cross-resistance in vitro. The reference strain was incubated 24 h and transferred 5 times after being exposed to 1 mM H2O2 in addition to a sub-MIC of each antibiotic by the agar dilution method. When cross-resistance to another antibiotic was confirmed, ampC, mexAB, and oprD expression and mutation of QRDR were investigated. Sub-MIC of piperacillin induced resistance to piperacillin and levofloxacin under stimulation with ROS. The mechanism of multi-resistance to β-lactams and levofloxacin was confirmed by RT-PCR. It was a decrease of oprD expression (p<0.05). The increase of MIC was inhibited by the ROS scavenger sodium zinc histidine dihydrolipoyl histidinate (DHL-His-Zn). In conclusion, for P. aeruginosa PAO1 to acquire multidrug resistance, stimulation with ROS was as important as exposure to sub-MIC of piperacillin.