Hiromitsu Fujiwara

First Streptococcus agalactiae Isolates Highly Resistant to Quinolones, with Point Mutations in gyrA and parC

ABSTRACT 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.

The indirect pathogenicity of Stenotrophomonas maltophilia.

Stenotrophomonas maltophilia has at least two inducible beta-lactamases, L1 and L2, which can hydrolyze almost all classes of beta-lactam antimicrobial agents. This study was done to verify the indirect pathogenicity of S. maltophilia that could promote the growth of other beta-lactam agent-susceptible bacteria in a mixed culture. We counted CFU of beta-lactam agent-susceptible bacteria under the presence of imipenem or ceftazidime in a pure culture and mixed culture with S. maltophilia. Our results showed that beta-lactamase leaking from S. maltophilia can encourage the growth of Serratia marcescens and Pseudomonas aeruginosa even if imipenem or ceftazidime was supplemented. This study discovered a blind spot in chemotherapy against an indirect pathogen such as S. maltophilia.