[Susceptibility of vertically transmitted Group B streptococci to antimicrobial agents. Multicenter study].

INTRODUCTION

To investigate the susceptibility of group B streptococci (GBS) to macrolides and lincosamides and assess alternatives for intrapartum chemoprophylaxis in women allergic to penicillin and colonized by a GBS strain resistant to these antibiotics.

METHODS

Multicenter study performed with 131 strains isolated between 1997-2002 from newborns diagnosed with early-onset GBS disease and 479 strains collected in 2002 from the vagina or rectum of pregnant women.

RESULTS

All the GBS (100%) were susceptible to penicillin, ampicillin, vancomycin, quinupristin/dalfopristin, levofloxacin and teicoplanin. Resistance rates were as follows: 12.45% to erythromycin and azithromycin, 11.80% to clindamycin, 11.31%, to josamycin, 1.80% to telithromycin and 0.32% to fosfomycin. Seventy-nine strains had a constitutive MLSB phenotype of resistance, 4 an inducible MLSB phenotype, 3 an M phenotype and 3 were resistant to clindamycin but susceptible to macrolides. The MIC for erythromycin and azithromycin was > 32 mg/L in more than 85% of GBS strains with a constitutive MLSB phenotype, from 0.5 to 4 mg/L in those with an inducible MLSB, and 4 mg/L in those with phenotype M. Fifty-one telithromycin-sensitive strains (all with a constitutive MLSB phenotype) showed induced resistance to telithromycin when erythromycin was present. No significant differences in antimicrobial resistance were found between GBS strains producing invasive neonatal disease and maternal isolates, or among strains from different geographic areas.

CONCLUSIONS

The high rate of resistance to macrolides and lincosamides in our area makes susceptibility testing mandatory for GBS strains isolated from pregnant women allergic to penicillin.