MOLECULAR EPIDEMIOLOGY OF PENICILLIN-RESISTANT STREPTOCOCCUS-PNEUMONIAE ISOLATES RECOVERED IN ITALY FROM 1993 TO 1996

Thirty-nine penicillin-resistant Streptococcus pneumoniae isolates rec overed among the approximately 700 pneumococcal strains collected from 1993 to 1996 in central and northern Italy were analyzed for several characteristics, including serotype, antibiotic susceptibility profile , chromosomal relatedness (by using pulsed-field gel electrophoresis [ PFGE]), restriction fragment length polymorphism (RFLP) of the penicil lin-binding protein (PBP) genes 1A, 2X, and 2B, and the presence of a variety of antibiotic resistance genes (determined by hybridization wi th appropriate DNA probes). The MICs of penicillin for most of the iso lates (30 of 39) were high, in the range of 1 mu g/ml or higher, and t hese 30 isolates carried additional resistance traits to two or more d rugs (erythromycin, chloramphenicol, co-trimoxazole, and tetracycline) and expressed serotypes 9, 19, and 23 and three distinct PFGE pattern s, More than half (22 of 30) of the isolates for which MICs were high were identified as representatives of two widespread international epi demic clones of S. pneumoniae. The first one of these clones (seven is olates) expressed serotype 23F and possessed all properties characteri stic of the widespread Spanish/USA international clone. Seven addition al strains with serotype 19 also had the same PFGE pattern, PBP gene, and RFLP polymorphisms, and other properties typical of the serotype 2 3 Spanish/USA clone, suggesting that these strains were the products o f a capsular transformation event (from serotype 23F to serotype 19) i n which the Spanish/USA clone was the recipient. The second internatio nal clone was represented by eight serotype 9 isolates which were resi stant to penicillin and trimethoprim-sulfamethoxazole and had the mole cular properties of the French/Spanish epidemic clone, The remaining e ight isolates for which penicillin MICs were high appeared to represen t a hitherto-undescribed ''Italian'' clone; they had a novel PFGE type , unique RFLPs for the PBP genes, and resistance to tetracycline, trim ethoprim-sulfamethoxazole, and erythromycin, and the penicillin MICs f or these isolates were 2 to 4 mu g/ml.