Trends in drug resistance, serotypes, and molecular types of Streptococcus pneumoniae colonizing preschool-age children attending day care centers in Lisbon, Portugal: a summary of 4 years of annual surveillance

Abstract

Of the nasopharyngeal cultures recovered from 942 day care center (DCC) attendees in Lisbon, Portugal, 591 (62%) yielded Streptococcus pneumoniae during a surveillance performed in February and March of 1999. Forty percent of the isolates were resistant to one or more antimicrobial agents. In particular, 2% were penicillin resistant and 20% had intermediate penicillin resistance. Multidrug resistance to macrolides, lincosamides, and tetracycline was the most frequent antibiotype (17% of all isolates). Serotyping and molecular typing by pulsed-field gel electrophoresis were performed for 202 out of 237 drug-resistant pneumococci (DRPn). The most frequent serotypes were 6B (26%), 14 (22%), 19F (16%), 23F (10%), and nontypeable (12%). The majority (67%) of the DRPn strains were representatives of nine international clones included in the Pneumococcal Molecular Epidemiology Network; eight of them had been detected in previous studies. Fourteen novel clones were identified, corresponding to 26% of the DRPn strains. The remaining 7% of the strains were local clones detected in our previous studies. Comparison with studies conducted since 1996 in Portuguese DCCs identified several trends: (i) the rate of DRPn frequency has fluctuated between 40 and 50%; (ii) the serotypes most frequently recovered have remained the same; (iii) nontypeable strains appear to be increasing in frequency; and (iv) a clone of serotype 33F emerged in 1999. Together, our observations highlight that the nasopharynxes of children in DCCs are a melting pot of successful DRPn clones that are important to study and monitor if we aim to gain a better understanding on the epidemiology of this pathogen.

FIG. 1.

Distribution of antimicrobial resistance among S. pneumoniae isolates recovered in different day care centers. White bars, isolates resistant to penicillin; gray bars, isolates intermediately resistant to penicillin; dashed bars, isolates susceptible to penicillin but resistant to other antimicrobial agents; black bars, isolates susceptible to all antimicrobial agents tested.

FIG. 2.

PFGE profiles of some drug-resistant S. pneumoniae clones isolated from children attending day care centers in Lisbon, Portugal. The λ ladder and R6 are indicated and were used as molecular weight markers. Clonal types of strains identical to PMEN representatives are designated by the PFGE code letter and the PMEN code between the brackets; other clonal types are designated by the serotype and PFGE code letter. NT, nontypeable.

FIG. 3.

Comparison of 4 years of the study. White bars, isolates resistant to penicillin; light gray bars, isolates intermediately resistant to penicillin; dark gray bars, isolates susceptible to penicillin but resistant to other antimicrobial agents; black bars, isolates susceptible to all antimicrobial agents tested. The total number of pneumococci was 277, 354, 465, and 591 in the four consecutive years, respectively.