Emergence of a fluoroquinolone-resistant strain of Streptococcus pneumoniae in England

Objective: To determine the epidemiological relationship between pneumococci of serotype 9V, with reduced susceptibility to ciprofloxacin, penicillin and erythromycin, referred to the Reference Laboratory during 1997-2001. Methods: Isolates were characterized by multilocus sequence typing (MLST), PFGE, and sequencing of parC and gyrA. Relevant clinical data were sought. Results: Forty-eight isolates were received from nine laboratories in England, but 35 (73%) were from one laboratory in Birmingham, and were mostly from elderly patients receiving ofloxacin or ciprofloxacin for respiratory infections. There were two quinolone resistance phenotypes, with ciprofloxacin, moxifloxacin and gemifloxacin MICs of 8-32, 0.5-1 and 0.125-0.25 mg/L, and 64-256, 4-16 and 1-4 mg/L, respectively. Each of three isolates from the former group had mutations in parC, whereas each of nine isolates from the more resistant group had mutations in both parC and gyrA. Several also had increased quinolone efflux. Typing of 27 quinolone-resistant isolates showed that eight were indistinguishable from the epidemic Spain(9V)-3 (ST156) clone, while the remainder belonged to a novel but related type (ST609), that differed from Spain(9V)-3 at 2/7 alleles (2 bp changes in aroE and 1 bp change in gdh). Both MLST types were represented among isolates with high- and low-level quinolone resistance. Three of five serotype 9V isolates from Birmingham, with reduced susceptibility to penicillin and erythromycin, and ciprofloxacin MICs of 1-2 mg/L, belonged to MLST type ST609, while another was indistinguishable from the Spain(9V)-3 clone. Review of records of 32 patients from Birmingham indicated that some isolates were nosocomial, whereas others were acquired in the community. Conclusions: In the late 1990s, a quinolone-resistant strain, clonally related to Spain(9V)-3, emerged in England, principally in Birmingham.