Abstract
BackgroundStreptococcus 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.MethodsFifty-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 Chi2 and Fisher’s exact test. Clustering was performed using Bionumerics version 6.5.ResultsMLST 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.ConclusionsThere 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.
Highlights
Streptococcus pneumoniae serotype 5 is among the most common serotypes causing invasive pneumococcal disease (IPD) in The Gambia
Study area and ethical statement The Pneumococcal Surveillance Project (PSP), hosted by the Medical Research Council Unit (MRC) in collaboration with the Gambian government is aimed at evaluating the effectiveness of the introduction of pneumococcal conjugate vaccine (PCV) into The Gambia
Database showed that both sequence types (ST) 3404 and ST 3339 were unique to Gambia and Senegal (Fig. 1), implying a recent and local differentiation event
Summary
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. 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. Two-thirds of its 2236 open reading frames have been assigned roles based on their predicted gene products [2, 3]. Conserved proteins with unknown functions constitute 16 % of S. pneumoniae’s open reading frames, of which, 20 % are unique to S. pneumoniae [2, 3]. Genetic information between strains can vary by up to 10 % [2, 4]
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