SmaI macrorestriction analysis of Italian isolates of erythromycin-resistant Streptococcus pyogenes and correlations with macrolide-resistance phenotypes.
High rates of erythromycin resistance among Streptococcus pyogenes strains have been reported in Italy in the last few years. In this study, 370 erythromycin-resistant (MIC, > or = 1 microg/mL) Italian isolates of this species obtained in 1997-1998 from throat swabs from symptomatic patients were typed by analyzing SmaI macrorestriction fragment patterns by pulsed-field gel electrophoresis (PFGE). Among the typable isolates (n = 341; the genomic DNA of the remaining 29 isolates was not restricted by SmaI), 48 distinct PFGE types were recognized, of which 31 were recorded in only one isolate (one-strain types). Fifty-two percent of typable isolates fell into three type clusters and 75% into six, suggesting that erythromycin-resistant group A streptococci circulating in Italy are polyclonal, but the majority of them probably derives from the spread of a limited number of clones. In parallel experiments, the 370 test strains were characterized for the macrolide resistance phenotype: 80 were assigned to phenotype cMLS, 89 to phenotype iMLS-A, 33 to phenotype iMLS-B, 11 to phenotype iMLS-C, and 157 to phenotype M. There was a close correlation between these phenotypic data and the genotypic results of PFGE analysis, the vast majority of the isolates assigned to individual PFGE classes belonging usually to a single phenotype of macrolide resistance. All of the 29 untypable isolates belonged to the M phenotype. Further correlations were observed with tetracycline resistance.
Ripa
S
S
Department of MCA Biology, University of Camerino, Italy.
Zampaloni
C
C
Vitali
L A
LA
Giovanetti
E
E
Montanari
M P
MP
Prenna
M
M
Varaldo
P E
PE
D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D015252:Deoxyribonucleases, Type II Site-Specific / Q000235:genetics*; D016521:Electrophoresis, Gel, Pulsed-Field; D004917:Erythromycin / Q000494:pharmacology*; D006801:Humans; D007558:Italy; D008826:Microbial Sensitivity Tests; D010641:Phenotype; D015183:Restriction Mapping; D013290:Streptococcal Infections / Q000453:epidemiology / Q000382:microbiology*; D013297:Streptococcus pyogenes / Q000187:drug effects*; D013753:Tetracycline Resistance
D000900:Anti-Bacterial Agents; D004917:Erythromycin; C025651:CCCGGG-specific type II deoxyribonucleases; D015252:Deoxyribonucleases, Type II Site-Specific