Topoisomerase sequences of coagulase-negative staphylococcal isolates resistant to ciprofloxacin or trovafloxacin - PubMed (original) (raw)

Topoisomerase sequences of coagulase-negative staphylococcal isolates resistant to ciprofloxacin or trovafloxacin

D T Dubin et al. Antimicrob Agents Chemother. 1999 Jul.

Abstract

Coagulase-negative staphylococcal isolates (n = 188) were screened for susceptibility to oxacillin, ciprofloxacin, and trovafloxacin, a new fluoroquinolone. At an oxacillin concentration of >/=4 microg/ml, 43% were methicillin resistant; of these, 70% were ciprofloxacin resistant (MIC, >/=4 microg/ml). Of the methicillin-resistant, ciprofloxacin-resistant isolates, 46% were susceptible to </=2 microg of trovafloxacin per ml and 32% were susceptible to </=1 microg of trovafloxacin per ml. Sixteen isolates, including twelve that expressed fluoroquinolone resistance, were chosen for detailed analysis. Identification of species by rRNA sequencing revealed a preponderance of Staphylococcus haemolyticus and S. hominis among fluoroquinolone-resistant strains. Segments of genes (gyrA and grlA) encoding DNA gyrase and DNA topoisomerase IV were sequenced. Considerable interspecies variation was noted, mainly involving noncoding nucleotide changes. Intraspecies variation consisted of coding changes associated with fluoroquinolone resistance. As for S. aureus, ciprofloxacin resistance (MIC, >/=8 microg/ml) and increased trovafloxacin MICs (0.25 to 2 microg/ml) could be conferred by the combined presence of single mutations in each gyrA and grlA gene. Trovafloxacin MICs of >/=8 microg/ml also occurred, but these required an additional mutation in grlA.

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Figures

FIG. 1

FIG. 1

Oxacillin and ciprofloxacin susceptibility distributions of coagulase-negative staphylococcal isolates compared to contemporary S. aureus isolates. The data are from the present study (A and C) and from a parallel study on S. aureus (12) (B and D). Here and in Fig. 2 the columns designated 0.125 represent MICs of ≤0.125 μg/ml.

FIG. 2

FIG. 2

Relationships between trovafloxacin and ciprofloxacin susceptibilities for methicillin-susceptible and -resistant coagulase-negative staphylococcal isolates. Ciprofloxacin MICs (ascending right to left) are plotted against trovafloxacin MICs (ascending front-to-back) for methicillin-susceptible (A) and methicillin-resistant (B) CoNS. Trovafloxacin-resistant and -intermediate isolates (MIC, ≥4 μg/ml) are indicated by the red columns.

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