Selection of a gyrA mutant of Mycobacterium tuberculosis resistant to fluoroquinolones during treatment with ofloxacin.

A strain of Mycobacterium tuberculosis resistant to ofloxacin was selected in a patient with a long history of multidrug-resistant tuberculosis eventually treated by ofloxacin combined with other second-line drugs. A mutation in the gyrA gene was hypothesized to be the mechanism of acquired resistance to ofloxacin in this strain. Chromosomal DNA of strains MTB1, isolated before treatment and susceptible to ofloxacin (MIC, 1 microgram/mL), and MTB2, isolated during treatment and resistant to ofloxacin (MIC, 32 micrograms/mL), was amplified by polymerase chain reaction (PCR) using two oligonucleotide primers highly homologous to DNA sequences flanking the quinolone resistance-determining region in gyrA of mycobacteria. Comparison of the nucleotide sequences of the 150-bp fragments obtained by PCR revealed a point mutation in MTB2 leading to the substitution of histidine for aspartic acid at a position corresponding to residues involved in quinolone resistance in Escherichia coli (Asp87), Staphylococcus aureus (Glu88), and Campylobacter jejuni (Asp90).