SUSCEPTIBILITY TO MACROLIDE AND BETA-LACTAM ANTIBIOTICS OF STREPTOCOCCUS-PYOGENES STRAINS ISOLATED OVER A 4-YEAR PERIOD IN CENTRAL ITALY

In vitro susceptibility to erythromycin, azithromycin, penicillin G, c eftriaxone and ceftibuten was investigated in 190 Streptococcus pyogen es strains isolated over a 4-year period (1998-1994) from patients att ending a university hospital located in central Italy. The rate of sus ceptibility to macrolide antibiotics of the S. pyogenes strains showed a progressive decrease (from 90.3% in 1991 to 79.5% in 1994), while a ll strains were susceptible to the three beta-lactam antibiotics. Owin g to the reduced prevalence of macrolide-susceptible S. pyogenes strai ns, in vitro susceptibility testing of streptococcal isolates appears to be always necessary before starting a macrolide-based chemotherapy. Concerning beta-lactams, ceftriaxone presented minimum inhibitory con centrations (MIG) always equal to or lower than those of penicillin G, while the oral long-acting cephalosporin, ceftibuten, had MICs higher than those of the other beta-lactams, although in the susceptible ran ge. Results of in vitro susceptibility testing are discussed in relati on to their implications for antimicrobial chemotherapy of S. pyogenes infections.