Selection of a gyra mutant of mycobacterium tuberculosis resistant to fluoroquinolones during treatment with ofloxacin

A strain of Mycobacterium tuberculosisb resistant to ofloxacin was selected in a patient with a long history of multidrug-resistant tuberculosis eventually treatedby ofloxacin combined with other second-line drugs. A mutation in the gyrA gene was hypothesized to bethe mechanism of acquired resistance to ofloxacin in this strain. Chromosomal DNA of strains MTBl, isolated before treatment and susceptible to ofloxacin (MIC, 1 μg /mL), and MTB2, isolated during treatment and resistant to ofloxacin (MIC, 32 μg /mL), was amplified by polymerase chainreaction (PCR) using two oligonucleotide primers highly homologous to DNA sequences flanking the quinolone resistance-determiningregion in gyrA of mycobacteria. Comparison of the nucleotide sequences of the 150-bp fragments obtained bypeR revealeda point mutation in MTB2 leading to the substitution of histidine for aspartic acid at a positioncorresponding to residues involvedin quinolone resistance in Escherichia coli (Asp87), Staphylococcus aureus (Glu88), and Campylobacter jejuni (Asp90).