gyrA mutations in ciprofloxacin-resistant, methicillin-resistant Staphylococcus aureus from Indiana, Minnesota, and Tennessee.

Mutational changes occurring at amino acid codons 84 and 85 located in the gyrA gene of methicillin-resistant Staphylococcus aureus (MRSA) were studied using radiolabeled oligonucleotide probes to examine the incidence of these ciprofloxacin resistance determinants in 30 MRSA isolates from Indiana, Minnesota, and Tennessee. Four separate oligonucleotide probes, one each corresponding to the wild-type sequence, a mutation at codon 84 (nucleotide 251), a mutation at codon 85 (nucleotide 253), and mutations at both, were used to examine the total genomic DNA from each of the 30 isolates, which had been restricted, electrophoresed, and Southern blotted. The probes indicated that 15 of the 28 ciprofloxacin-resistant isolates gave results consistent with a single mutation at codon 84. Four of the 28 ciprofloxacin-resistant strains had results consistent with a mutation at codon 84 and possibly at codon 85. The two ciprofloxacin-sensitive isolates from Tennessee showed homology with the wild-type probe sequence. Five isolates (4, Minnesota; 1, Tennessee) had no homology with any probe. By oligonucleotide probes, ciprofloxacin-resistant MRSA from diverse geographic regions contained similar gyrA mutations at codons 84 or 85 in 19 of 28 ciprofloxacin-resistant isolates.