Baseline Epidemiology and Genetic Structure of Streptococcus pneumoniae Serotype 6D in Southern Israel Prior to Introduction of Pneumococcal Conjugate Vaccines

Abstract

We characterized Streptococcus pneumoniae serotype 6D from among previously identified S. pneumoniae serotype 6B strains from Jewish and Bedouin children in southern Israel during a decade before vaccination. S. pneumoniae serotype 6D isolates constituted 6.7% of the presumed S. pneumoniae serotype 6B isolates. S. pneumoniae serotype 6D strains belonged to 20 sequence types that were differentially distributed between the two ethnic groups.T he discovery of a new Streptococcus pneumoniae serotype, serotype 6C, led to the logical suggestion that recombination might also produce a new member of the serogroup 6 family which would have the wciP serotype 6B (wciP 6B ) allele that differentiates S. pneumoniae serotype 6B from S. pneumoniae serotype 6A and the wciN 6C allele (1, 2). This serotype, designated S. pneumoniae serotype 6D, has been detected in both nasal carriage and invasive isolates (2-11).The 7-and 13-valent pneumococcal conjugate vaccines (PCV7 and PCV13, respectively) were introduced into the Israeli national immunization program in 2009 and 2010, respectively. Preliminary in vitro data suggest that the S. pneumoniae serotype 6B component of these vaccines elicits antibodies that are cross-opsonic to S. pneumoniae serotype 6D (12). However, clinical data are not yet available to confirm these findings. Evaluation of the prevalence of S. pneumoniae serotype 6D before and after PCV implementation would indirectly determine whether these vaccines provide protection against S. pneumoniae serotype 6D. The aim of this study was therefore to identify S. pneumoniae serotype 6D strains from among previously characterized S. pneumoniae serotype 6B isolates, explore their molecular epidemiology, and determine the circulation of S. pneumoniae serotype 6D clones among the members of two distinct ethnic subpopulations.This retrospective study was conducted in southern Israel during the decade (1999 to 2008) preceding PCV7 implementation. The study population included children Ͻ5 years of age: Jewish children with lifestyles resembling those of populations in developed countries and Muslim Bedouin children with standards of living resembling those of populations in developing countries (13). Contact between children of the two populations is rare. S. pneumoniae was cultured from four isolation sites: blood/cerebrospinal fluid (CSF), middle ear fluid (MEF), conjunctiva, and nasopharynx (14). Identification, antimicrobial susceptibility testing, and serotyping were performed as previously described (13). A PCR system targeting both wciN 6C (wciN ␤ ) and wciP 6B (wciP584a) was used to segregate S. pneumoniae serotype 6D from S. pneumoniae serotype 6B (2).Of 1,628 presumed S. pneumoniae serotype 6B isolates, 1,593 (97.9%) pneumococci, isolated from 1,201 children, were available for S. pneumoniae serotype 6D typing by PCR. S. pneumoniae serotype 6D was identified in 98/1,201 (8.2%) individuals, of which 41 individuals also presented S. pneumoniae serotype 6B during the study period. Overall, S. pneumoniae serotype 6D con...

Field Evaluation of Culture plus Latex Sweep Serotyping for Detection of Multiple Pneumococcal Serotype Colonisation in Infants and Young Children

“…Pneumococcal serotype 6D has also been described recently: this serotype may be identified as 6B using currently available antisera [14], [15]. There are no data regarding prevalence of this serotype in the study population, although given the absence of PCV use, carriage this serotype was unlikely to be common and thus antisera 6B isolates have been reported as such [16], [17]. Although commonly carried in the nasopharynx, non-typeable pneumococci were excluded from these comparisons, since the latex sweep method has no confirmatory test of pneumococcal identity except the presence of capsule.…”