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Applied and Environmental Microbiology, September 2006, p. 5790-5793, Vol. 72, No. 9
0099-2240/06/$08.00+0     doi:10.1128/AEM.03032-05

Transformation of the Antibacterial Agent Norfloxacin by Environmental Mycobacteria

Michael D. Adjei,1,{dagger} Thomas M. Heinze,2 Joanna Deck,1 James P. Freeman,2 Anna J. Williams,1 and John B. Sutherland1*

Divisions of Microbiology,1 Biochemical Toxicology, National Center for Toxicological Research, U.S. Food and Drug Administration, Jefferson, Arkansas2

Received 23 December 2005/ Accepted 18 June 2006

Because fluoroquinolone antimicrobial agents may be released into the environment, the potential for environmental bacteria to biotransform these drugs was investigated. Eight Mycobacterium sp. cultures in a sorbitol-yeast extract medium were dosed with 100 µg ml–1 of norfloxacin and incubated for 7 days. The MICs of norfloxacin for these strains, tested by an agar dilution method, were 1.6 to 25 µg ml–1. Cultures were extracted with ethyl acetate, and potential metabolites in the extracts were purified by high-performance liquid chromatography. The metabolites were identified using mass spectrometry and nuclear magnetic resonance spectroscopy. N-Acetylnorfloxacin (5 to 50% of the total absorbance at 280 nm) was produced by the eight Mycobacterium strains. N-Nitrosonorfloxacin (5 to 30% of the total absorbance) was also produced by Mycobacterium sp. strain PYR100 and Mycobacterium gilvum PYR-GCK. The MICs of N-nitrosonorfloxacin and N-acetylnorfloxacin were 2- to 38- and 4- to 1,000-fold higher, respectively, than those of norfloxacin for several different bacteria, including the two strains that produced both metabolites. Although N-nitrosonorfloxacin had less antibacterial activity, nitrosamines are potentially carcinogenic. The biotransformation of fluoroquinolones by mycobacteria may serve as a resistance mechanism.

* Corresponding author. Mailing address: National Center for Toxicological Research, U.S. Food and Drug Administration, 3900 NCTR Road, Jefferson, AR 72079. Phone: (870) 543-7059. Fax: (870) 543-7307. E-mail: john.sutherland{at}fda.hhs.gov.

{dagger} Present address: Norfolk Department of Public Health, 830 Southampton Ave., Norfolk, VA 23510.

Applied and Environmental Microbiology, September 2006, p. 5790-5793, Vol. 72, No. 9
0099-2240/06/$08.00+0     doi:10.1128/AEM.03032-05




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