First Streptococcus agalactiae isolates highly resistant to quinolones, with point mutations in gyrA and parC.

Three isolates of Streptococcus agalactiae highly resistant to multiple fluoroquinolones were isolated in Japan. Compared with susceptible strains of S. agalactiae, these quinolone-resistant strains had double point mutations within the quinolone resistance-determining regions of gyrA and parC; Ser-81 was changed to Leu (TCA --> TTA) in the amino acid sequence deduced from gyrA, and Ser-79 was changed to Phe (TCC --> TTC) in the amino acid sequence deduced from parC. Comparative sequence analysis revealed the possibility of gene transfer between S. agalactiae and another beta-hemolytic streptococcus, Streptococcus difficile.