Adaptive response of Vibrio cholerae and Escherichia coli to nitrofurantoin

Pretreatment with sublethal doses of nitrofurantoin induced adaptive response in both Vibrio cholerae and Escherichia coli cells as indicated by their greater resistance to the subsequent challenging doses of the same drug. Adaptive response was maximum corresponding to pretreatment drug concentrations of 0.40 microgram/ml and 0.015 microgram/ml respectively for V. cholerae OGAWA 154 (wild type) and E. coli K-12 AB 2463 (recA-) cells. Adaptive response was inhibited by chloramphenicol (100 micrograms/ml) indicating the need of concomitant protein synthesis. Induction of adaptive response in recA deficient E. coli cells indicated that it was different from the conventional "SOS" response. Melting temperature of DNA of V. cholerae cells subjected to adaptive (0.4 microgram/ml for 1 hr) and challenging (120 micrograms/ml for 1 hr) doses of nitrofurantoin (76 degrees C) was closer to that of native DNA (75 degrees C) vis-a-vis DNA isolated from nonadapted and drug treated cells (77.5 degrees C). Also, DNA isolated from V. cholerae cells subjected to adaptive and challenging doses of the drug revealed the presence of fewer interstrand cross-links (16% reversible DNA) vis-a-vis DNA from nonadapted but drug treated cells (55% reversible DNA). Photomicrographic studies revealed that V. cholerae cells that were nonadapted but drug treated grew into long filamentous forms (4.25 +/- 2.97 micron) whereas those subjected to both adaptive and challenge doses of the drug exhibited much less filamentation (2.08 +/- 0.84 micron) vis-a-vis native cells (1.42 +/- 0.5 micron). Similar results on DNA melting temperature, cross-links in DNA, and filamentation of cells were obtained for E. coli AB 2463 (recA-) cells subjected to adaptive and challenging treatments with nitrofurantoin. Almost equal degree of resistance against nitrofurantoin could be induced in both V. cholerae OGAWA 154 (wild type) and E. coli strain PJ3 (AB 1157 ada-) when these cells were pretreated with nontoxic doses of hydrogen peroxide or nitrofurantoin. Evidence obtained in this work on the nature of the nitrofuratoin induced adaptive response with particular references to the oxidative and/or alkylating DNA damages were discussed. Nitrofuratoin induced adaptive response appeared similar to that elicited by furazolidone in V. cholerae cells and appeared to be directed towards oxidative and not alkylating adaptive repair pathway.