Population structure, epidemiology and antibiotic resistance patterns of Streptococcus pneumoniae serotype 5: prior to PCV-13 vaccine introduction in Eastern Gambia

Abstract

Background

Streptococcus pneumoniae serotype 5 is among the most common serotypes causing invasive pneumococcal disease (IPD) in The Gambia. We anticipate that introduction of the 13-valent pneumococcal conjugate vaccine (PCV-13) into routine vaccination in The Gambia will reduce serotype 5 IPD. However, the emergence of new clones that have altered their genetic repertoire through capsular switching or genetic recombination after vaccination with PCV-13 poses a threat to this public health effort. In order to monitor for potential genetic changes post-PCV-13 vaccination, we established the baseline population structure, epidemiology, and antibiotic resistance patterns of serotype 5 before the introduction of PCV-13.

Methods

Fifty-five invasive S. pneumoniae serotype 5 isolates were recovered from January 2009 to August 2011 in a population-based study in the Upper River Region of The Gambia. Serotyping was done by latex agglutination and confirmed by serotype-specific Polymerase Chain Reaction (PCR). Genotyping was undertaken using Multilocus Sequence Typing (MLST). Antimicrobial sensitivity was done using disc diffusion. Contingency table analyses were conducted using Pearson’s Chi ² and Fisher’s exact test. Clustering was performed using Bionumerics version 6.5.

Results

MLST resolved S. pneumoniae serotype 5 isolates into 3 sequence types (ST), namely ST 289(6/55), ST 3339(19/55) and ST 3404(30/55). ST 289 was identified as the major clonal complex. ST 3339, the prevalent genotype in 2009 [84.6 % (11/13)], was replaced by ST 3404 [70.4 % (19/27)] in 2010 as the dominant ST. Interestingly, ST 3404 showed lower resistance to tetracycline and oxacillin ( P < 0.001), an empirical surrogate to penicillin in The Gambia.

Conclusions

There has been an emergence of ST 3404 in The Gambia prior to the introduction of PCV-13. Our findings provide important background data for future assessment of the impact of PCV-13 into routine immunization in developing countries, such as The Gambia.