Antibiotic-resistant invasive pneumococcal clones in Italy

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/ST63 [corrected] 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/ST63 [corrected] 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.

FIG. 1.

Phylogenetic analysis of PFGE profiles obtained among the 105 S. pneumoniae isolates. The dendrogram was constructed with PFGE profiles by similarity and clustering analysis using the unweighted pair-group method with arithmetic averages and the Dice coefficient. The genetic similarity in percentages is showed above the dendrogram. Strain code, serotype, PFGE type and subtype, and ST are marked on the right. “(P)” indicates penicillin nonsusceptibility.