Staphylococcus aureus mutants isolated via exposure to nonfluorinated quinolones: detection of known and unique mutations.
The in vitro development of resistance to the new nonfluorinated quinolones (NFQs; PGE 9262932, PGE 4175997, and PGE 9509924) was investigated in Staphylococcus aureus. At concentrations two times the MIC, step 1 mutants were isolated more frequently with ciprofloxacin and trovafloxacin (9.1 x 10(-8) and 5.7 x 10(-9), respectively) than with the NFQs, gatifloxacin, or clinafloxacin (<5.7 x 10(-10)). Step 2 and step 3 mutants were selected via exposure of a step 1 mutant (selected with trovafloxacin) to four times the MICs of trovafloxacin and PGE 9262932. The step 1 mutant contained the known Ser80-Phe mutation in GrlA, and the step 2 and step 3 mutants contained the known Ser80-Phe and Ser84-Leu mutations in GrlA and GyrA, respectively. Compared to ciprofloxacin, the NFQs were 8-fold more potent against the parent and 16- to 128-fold more potent against the step 3 mutants. Mutants with high-level NFQ resistance (MIC, 32 microg/ml) were isolated by the spiral plater-based serial passage technique. DNA sequence analysis of three such mutants revealed the following mutations: (i) Ser84-Leu in GyrA and Glu84-Lys and His103-Tyr in GrlA; (ii) Ser-84Leu in GyrA, Ser52-Arg in GrlA, and Glu472-Val in GrlB; and (iii) Ser84-Leu in GyrA, Glu477-Val in GyrB, and Glu84-Lys and His103-Tyr in GrlA. Addition of the efflux pump inhibitor reserpine (10 microg/ml) resulted in 4- to 16-fold increases in the potencies of the NFQs against these mutants, whereas it resulted in 2-fold increases in the potencies of the NFQs against the parent.
Roychoudhury
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S
Health Care Research Center, Procter & Gamble Pharmaceuticals, Mason, Ohio 45040, USA. roychoudhury.s@pg.com
Twinem
T L
TL
Makin
K M
KM
Nienaber
M A
MA
Li
C
C
Morris
T W
TW
Ledoussal
B
B
Catrenich
C E
CE
D042462:4-Quinolones; D000890:Anti-Infective Agents / Q000494:pharmacology*; D004269:DNA, Bacterial / Q000032:analysis; D005798:Genes, Bacterial; D005838:Genotype; D008826:Microbial Sensitivity Tests; D009154:Mutation / Q000235:genetics; D013211:Staphylococcus aureus / Q000187:drug effects / Q000235:genetics*
D042462:4-Quinolones; D000890:Anti-Infective Agents; D004269:DNA, Bacterial