Contribution of reactive oxygen species to pathways of quinolone-mediated bacterial cell death.
BACKGROUND
Quinolone-mediated death of Escherichia coli has been proposed to occur by two pathways. One is blocked by inhibitors of protein synthesis; the other is not. It is currently unknown how these two pathways fit with the recent observation that hydroxyl radical accumulation is associated with quinolone lethality.


METHODS
E. coli was treated with thiourea plus 2,2'-bipyridyl to block hydroxyl radical accumulation, and the effect on quinolone lethality was measured for quinolones that distinguished the two lethal pathways: oxolinic acid requires protein synthesis to kill E. coli, while PD161144, a C-8-methoxy fluoroquinolone, does not. The lethal activity of another fluoroquinolone, moxifloxacin, was partially blocked by the presence of chloramphenicol, an inhibitor of protein synthesis. That feature made it possible to determine whether the effects of chloramphenicol and thiourea plus 2,2'-bipyridyl were additive.


RESULTS
Lethal activity of oxolinic acid was completely blocked by thiourea plus 2,2'-bipyridyl and by chloramphenicol. In contrast, PD161144 lethality was unaffected by these treatments. With moxifloxacin, both chloramphenicol and thiourea plus 2,2'-bipyridyl separately exhibited the same partial inhibition of quinolone lethality. No additivity in protection from moxifloxacin lethality was observed when thiourea, 2,2'-bipyridyl and chloramphenicol were combined and compared with the effect of chloramphenicol or thiourea plus 2,2'-bipyridyl used separately.


CONCLUSIONS
Inhibitor studies indicated that hydroxyl radical action contributes to quinolone-mediated cell death occurring via the chloramphenicol-sensitive lethal pathway but not via the chloramphenicol-insensitive pathway.
Wang
Xiuhong
X
Public Health Research Institute, New Jersey Medical School, UMDNJ, 225 Warren Street, Newark, NJ 07103, USA.
Zhao
Xilin
X
Malik
Muhammad
M
Drlica
Karl
K
D015082:2,2'-Dipyridyl / Q000494:pharmacology; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001372:Aza Compounds / Q000494:pharmacology; D002701:Chloramphenicol / Q000494:pharmacology; D004926:Escherichia coli / Q000187:drug effects* / Q000378:metabolism*; D024841:Fluoroquinolones; D050296:Microbial Viability / Q000187:drug effects*; D000077266:Moxifloxacin; D010093:Oxolinic Acid / Q000494:pharmacology; D011804:Quinolines / Q000494:pharmacology; D015363:Quinolones / Q000494:pharmacology*; D017382:Reactive Oxygen Species / Q000378:metabolism* / Q000633:toxicity*
D000900:Anti-Bacterial Agents; D001372:Aza Compounds; D024841:Fluoroquinolones; D011804:Quinolines; D015363:Quinolones; D017382:Reactive Oxygen Species; D015082:2,2'-Dipyridyl; D002701:Chloramphenicol; D010093:Oxolinic Acid; D000077266:Moxifloxacin