Antibiotic-resistant invasive pneumococcal clones in Italy

A total of 105 multiple-antibiotic-resistant invasive pneumococcal isolates recovered in Italy from 2001 to2003 were genetically characterized. Of these, 40 were penicillin-nonsusceptible (PNSSP) and 65 were penicillin-susceptible (PSSP) Streptococcus pneumoniae strains. Among the PNSSP isolates, 8 and 11 differentrestriction profiles were obtained for the pbp2b and pbp2x genes, respectively. Clonal groups were establishedon the basis of analysis of both pulsed-field gel electrophoresis (PFGE) types and multilocus sequence typing(MLST). Several international clones, such as Spain23F-1/ST81, Spain6B-2/ST90, Spain9V-3/ST156, andSweden15A-25/ST263, were identified among the PNSSP isolates. Other, smaller clones, such as the minorSpanish 19F clone/ST88 and Denmark14-32/ST230, were also found. Among the PSSP isolates, clones relatedto England14-9/ST9, Greece6B-22/ST273, and Portugal19F-21/ST177 were found. In addition, two large clonescomprised nonvaccine serotypes. One, comprising serotype 3 isolates, corresponded to the clone Netherlands3-31/ST180; the other, comprising serotype 15B/C isolates, ST474, was not related to any previously describedclone. Two small clusters related to the newly described clones Greece21-30/ST193 and Netherlands15B-37/ST199 included isolates with unrelated PFGE profiles. An unusual finding was the inability to obtain the MLSTallelic profile for an isolate of serotype 19A, belonging to the Sweden15A-25/ST263 clone, due to a large deletionof the xpt gene. Capsular switching was observed among both PNSSP and PSSP isolates and involved alsoserotypes not included in the 7-valent pneumococcal conjugate vaccine (PCV7), such as serotypes 15B/C and19A. Since antibiotic-resistant nonvaccine serotype clones are present in Italy, continuous monitoring ofpneumococcal epidemiology should be carried out in the PCV7 era.