Antibiotic-Resistant Invasive Pneumococcal Clones in Italy

Abstract

ABSTRACT A total of 105 multiple-antibiotic-resistant invasive pneumococcal isolates recovered in Italy from 2001 to 2003 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 different restriction profiles were obtained for the pbp2b and pbp2x genes, respectively. Clonal groups were established on the basis of analysis of both pulsed-field gel electrophoresis (PFGE) types and multilocus sequence typing (MLST). Several international clones, such as Spain 23F -1/ST81, Spain 6B -2/ST90, Spain 9V -3/ST156, and Sweden 15A -25/ST263, were identified among the PNSSP isolates. Other, smaller clones, such as the minor Spanish 19F clone/ST88 and Denmark 14 -32/ST230, were also found. Among the PSSP isolates, clones related to England 14 -9/ST9, Greece 6B -22/ST273, and Portugal 19F -21/ST177 were found. In addition, two large clones comprised nonvaccine serotypes. One, comprising serotype 3 isolates, corresponded to the clone Netherlands 3 -31/ST180; the other, comprising serotype 15B/C isolates, ST474, was not related to any previously described clone. Two small clusters related to the newly described clones Greece 21 -30/ST193 and Netherlands 15B -37/ST199 included isolates with unrelated PFGE profiles. An unusual finding was the inability to obtain the MLST allelic profile for an isolate of serotype 19A, belonging to the Sweden 15A -25/ST263 clone, due to a large deletion of the xpt gene. Capsular switching was observed among both PNSSP and PSSP isolates and involved also serotypes not included in the 7-valent pneumococcal conjugate vaccine (PCV7), such as serotypes 15B/C and 19A. Since antibiotic-resistant nonvaccine serotype clones are present in Italy, continuous monitoring of pneumococcal epidemiology should be carried out in the PCV7 era.