Dengue and Relative Bradycardia

a molecule-dependent target specifi city: mutations in parC are generally selected by pefl oxacin, ciprofl oxacin, and levofl oxacin, and those in gyrA are selected by sparfl oxacin, gatifl oxacin, moxifl oxacin, gemifl oxacin, and garenoxacin (5). In second-step mutants, mutations are present in both parC and gyrA and confer resistance to the antistreptococcal FQs levofl oxacin, moxifl oxacin, and gatifl oxacin. FQ resistance in GBS has been reported in Japan, the United States, and Spain (6–8). Up to now, all FQresistant GBS strains described were highly resistant because of point mutations in gyrA and parC QRDR; a parC mutation at position 79 was present in all strains. These strains were isolated from elderly adults who, in some cases, had received quinolone therapy. Low-level resistance to FQ in GBS CNR0717 was associated with a Ser 79 → Tyr mutation in parC. Therefore, although the FQ sensitivity of this strain is unknown, a fi rst-step mutant could have been selected in vivo as our patient was treated with levofl oxacin for 2 weeks. GBS is an unusual cause of acute bacterial exacerbation of chronic bronchitis compared with other respiratory pathogens such as S. pneumoniae, but pathologies associated with this bacterium are changing. Clinical microbiologists should be aware of these changes and test isolates of Streptococcus spp. for susceptibility to FQs. This report indicates that FQ resistance among streptococci is a growing concern and that levofl oxacin can select in vivo parC fi rst-step mutants that will facilitate emergence of high-level FQresistant GBS strains, as demonstrated in vitro for S. pneumoniae (9). Finally, although FQ treatment is recommended for high-risk groups with acute exacerbations of chronic bronchitis, these antimicrobial drugs must be reserved for situations in which there are no effective alternative drugs to treat infections caused by multidrug-resistant bacteria. For susceptible strains, β-lactams, which still constitute the fi rst-line recommended antimicrobial drugs, should be used for treatment of these patients (10).