Identification, prevalence and population structure of non-typable Streptococcus pneumoniae in carriage samples isolated from preschoolers attending day-care centres.

The authors aimed to get insights into the population structure of non-(sero)typable pneumococci (NTPn), a specific group of natural atypical pneumococci whose identification is often difficult, and which has remained insufficiently studied. A total of 265 presumptive NTPn, isolated between 1997 and 2003 from the nasopharynx of children, were characterized. Strains were confirmed to be pneumococci on the basis of bile solubility, and PCR detection or Southern blotting hybridization of lytA and psaA, genes ubiquitous in this species. Multilocus sequence typing (MLST) was used to exclude two isolates that gave ambiguous results. Non-typability was confirmed by the Quellung reaction using Omniserum. A total of 213 isolates were considered to be true NTPn. The molecular analysis of the true NTPn by PFGE and MLST showed that this population was genetically diverse, although a dominant cluster, accounting for 66 % of the isolates, was identified. Antimicrobial resistance was observed in most genetic backgrounds, and multidrug resistance to penicillin, erythromycin, clindamycin, tetracycline and sulfamethoxazole-trimethoprim was associated with strains belonging to the dominant cluster. Comparison with PFGE fingerprints and sequence types of large collections of serotypable strains showed that the genetic backgrounds of all but two NTPn were different from those found in serotypable strains. In addition, we found that NTPn strains with similar genetic backgrounds to those identified in our study had been isolated from disease sources in other countries. These observations seem to indicate that NTPn have diverse genetic backgrounds and may have evolved as a distinct group of pneumococcal isolates.

Properties of novel international drug-resistant pneumococcal clones identified in day-care centers of Lisbon, Portugal.

In this study, 61 drug-resistant Streptococcus pneumoniae strains were characterized by multilocus sequence typing (MLST). These strains were representatives of 26 major clones (defined using pulsed-field gel electrophoresis) accounting for 93% of the 1,285 drug-resistant Streptococcus pneumoniae isolates recovered from the nasopharynges of healthy children attending day-care centers in Lisbon during 2001 to 2003. Using MLST, 13 of the 26 clones were found to be identical or closely related to 11 Pneumococcal Molecular Epidemiology Network (PMEN) clones, 4 clones were found to be unique as there were no identical or highly related allelic profiles deposited in the MLST database, and the remaining 9 clones had sequence types that matched or differed at a single or double locus from allelic profiles available in the MLST database. These nine clones were of serotypes 33F, 10A, 19A, 19F, 6A, 20, 24F, and 3, one was nontypeable, and, by MLST, they were found to be identical or highly related to isolates from disease origin that were dispersed internationally. Since the majority of these clones had serotypes that are not included in the 7-valent conjugate pneumococcal vaccine, monitoring of these clones is important for surveying their possible spread in the future. We propose the inclusion of these novel international clones in the PMEN.

Effect of the seven-valent conjugate pneumococcal vaccine on carriage and drug resistance of Streptococcus pneumoniae in healthy children attending day-care centers in Lisbon.

AIMS: Prospective study to evaluate the impact of the 7-valent pneumococcal conjugate vaccine (Prevenar) on the nasopharyngeal (NP) carriage of drug-resistant Streptococcus pneumoniae (DRPn), by healthy children attending day-care centers (ages 6 months-6 years). METHODS: Vaccinees (238 children) who received vaccine and controls (457 children) were followed for carriage of total S. pneumoniae and DRPn and for the serotypes and genetic backgrounds of DRPn during 6 consecutive sampling periods between May 2001 and February 2003. RESULTS: We detected no significant differences between vaccinees and the control group in the total carriage rate of Pn (average, 68%) or in the frequency of carriage of DRPn (average, 38%), including the frequency of penicillin-nonsusceptible strains (average, 24%). In contrast, there was a decline in the carriage of DRPn with vaccine serotypes which was compensated by the appearance and gradual increase in the frequency of DRPn expressing unusual serotypes (6A, 10A, 15A and 15C, 19A, 23A, 33F) which were not present in the vaccine as well as an increase in nontypable strains. The majority of the DRPn with unusual serotypes showed different pulsed field gel electrophoresis patterns indicating replacement of the original resistant flora by other clonal types of drug-resistant bacteria. Antibiotic consumption and the frequency of respiratory tract infections were similar among the vaccinees and controls. CONCLUSIONS: Pneumococcal vaccination did not change the frequency of carriage of drug-resistant strains being the initially dominant vaccine serotypes replaced by others expressing nonvaccine serotypes. Reduction in the carriage of DRPn may require a combination of the conjugate vaccine and a decrease in antibiotic pressure.