Clonal diversity of invasive Streptococcus pneumoniae from Portuguese children

Abstract number: 1133_63

Serrano I., Carriço J., Aguiar S., Melo-Cristino J., Ramirez M.

Objective:  

To identify the clones responsible for invasive disease among Portuguese children.

Methods:  

A recent (1999–2002) collection of 82 invasive isolates recovered from children <6 years old in Portugal was characterized using a combination of macrorestriction profiling, using SmaI and pulsed field gel electrophoresis (PFGE), and multi-locus sequence typing (MLST). The Bionumerics software was used to make UPGMA (unweighed pair group method with arithmetic mean) dendrograms of PFGE fragment patterns. The dice similarity coefficient was used with optimization and position tolerance settings of 1.0 and 1.5%. Among the 18 serotypes detected, serotypes 14 (25.6%), 23F (17.1%), 1 (12.2%), and 6B (9.8%) were the most prevalent.

Results:  

We found 42 sequence types (ST), including 12 novel STs, corresponding to 27 different lineages by e-BURST analysis. By combining the PFGE and MLST data we were able to infer the genetic lineages of the majority of the isolates. Among serotype 14, most isolates (16/21) were clustered with the Spain9V-3 clone, including representatives of ST156, 557, and the new ST790. Another cluster with 4 strains included ST15, related to the England14-9 clone, and ST409. Among serotype 23F the majority of the isolates (12/14) were grouped into a single cluster that included ST338, the same ST as the Colombia23F-26 clone, and the new ST1371. Serotype 1 was clustered into two main lineages, one including representatives of ST306 and 228 (7/10), and the other ST304 and 350 (3/10). In serotype 6B most isolates (5/8) were included in a cluster with ST273 the same ST of the Greece6B-22 clone, and the new ST1224. The other strain was ST887 related to Poland6B-20. Among penicillin non-susceptible strains 80.5% were related to two lineages, Spain9V-3 expressing serotypes 14 and 9V (18/36) and Colombia23F-26 (11/36), and the remaining isolates belonged to other internationally disseminated clones - Spain23F-1, Greece6B-22, and Poland6B-20.

Conclusions:  

Representatives of 6 internationally disseminated clones were found among invasive isolates recovered from children <6 years old, accounting for 91.6% of the penicillin non-susceptible isolates. The most frequent lineages were related to Spain9V-3 (23.2%) and Colombia23F-26 (14.6%). This study provides a baseline for detecting potential effects of the use of the 7-valent conjugated vaccine on the distribution of individual genetic lineages within this population.