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 1,096Streptococcuspneumoniaerecovered from 2,111 nasopharyngeal samples ofchildrenattending 16daycarecenters(DCCs) in Lisbon, Portugal, and molecular typing of 413 drug-resistantpneumococci (DRPn) and 89 fully drug-susceptible pneumococci (DSPn) has allowed several conclusions. (i) There was an increase in the frequency of DRPncolonizingchildrenin DCCs from 40% in 1996 to 45% in 1997 to 50% in 1998. (ii) Drug resistance spread by cross-transmission of DRPn clones. A few (8 out of 57) DRPn clones were repeatedly isolated from a large number ofchildrenin several DCCs and during each period of surveillance, suggesting the epidemic nature of these clones, which included lineages representing internationally spread S.pneumoniaeclones. (iii) Dissemination of resistance determinants among pneumococcicolonizingthe nasopharynx occurred. Association of identical pulsed-field gel electrophoresispatternswith diverse antibiotypes among pneumococcicolonizingchildrensuggests that the high prevalence of DRPn involves not only cross-transmission ofresistantstrains but also dispersal of resistance genes through recombinational mechanisms. (iv) DCCs areautonomousepidemiologicalunits. Among the 413 DRPn, 57 different lineages were detected; these lineages were dispersed among the 16 DCCs to produce unique microbiological profiles for each of the DCCs. Highergeneticdiversityand less sharing ofclonaltypes were observed among the DSPn.