Genetic diversity and clonal patterns among antibiotic-susceptible and -resistant Streptococcus pneumoniae colonizing children: Day care centers as autonomous epidemiological units

Characterization by antibiotype of the 1,096 Streptococcus pneumoniae recov ered from 2,111 nasopharyngeal samples of children attending 16 day care ce nters (DCCs) in Lisbon, Portugal, and molecular typing of 413 drug-resistan t pneumococci (DRPn) and 89 fully drug-susceptible pneumococci (DSPn) has a llowed several conclusions. (i) There was an increase in the frequency of D RPn colonizing children in DCCs from 40% in 1996 to 45% in 1997 to 50% in 1 998. (ii) Drug resistance spread by cross-transmission of DRPn clones. A fe w (8 out of 57) DRPn clones were repeatedly isolated from a large number of children in several DCCs and during each period of surveillance, suggestin g the epidemic nature of these clones, which included lineages representing internationally spread S. pneumoniae clones. (iii) Dissemination of resist ance determinants among pneumococci colonizing the nasopharynx occurred. As sociation of identical pulsed-field gel electrophoresis patterns with diver se antibiotypes among pneumococci colonizing children suggests that the hig h prevalence of DRPn involves not only cross-transmission of resistant stra ins but also dispersal of resistance genes through recombinational mechanis ms. (iv) DCCs are autonomous epidemiological units. Among the 413 DRPn, 57 different lineages were detected; these lineages were dispersed among the 1 6 DCCs to produce unique microbiological profiles for each of the DCCs. Hig her genetic diversity and less sharing of clonal types were observed among the DSPn.