Pneumococcal vaccination does not affect the genetic diversity of Moraxella catarrhalis isolates in children.

Abstract

Moraxella catarrhalis is an acknowledged pathogen of the respiratory tract in both adults and children [1], occupying a similar niche to that of Streptococcus pneumoniae and Haemophilus influenzae. In a recent study, Veenhoven et al. [2] showed that toddlers and older children who had previously experienced episodes of acute otitis media (AOM) did not experience a reduction of AOM episodes when vaccinated with a conjugate pneumococcal vaccine followed by a polysaccharide pneumococcal vaccine. Moreover, the incidence of M. catarrhalis isolation did not differ between the two groups, while Staphylococcus aureus was isolated more often from children in the vaccinated group than from children in the control group vaccinated against hepatitis A or B (P=0.02). It was also noted that an “immediate and complete” replacement of S. pneumoniae vaccine serotypes by non-vaccine serotypes tended to occur within the vaccinated group. Since bacterial interference of M. catarrhalis by competing streptococcal species has been demonstrated in vitro [3], the present study was conducted to determine whether vaccination against S. pneumoniae (and its subsequent removal from the M. catarrhalis niche) had an effect in altering the genetic diversity of M. catarrhalis isolates compared to a control vaccinated group. During the course of the study, children were followed for a total of 18 months, with routine microbiological and clinical investigations occurring at 1, 7, 14, 20 and 26 months after vaccination as well as during any episode of AOM. Bacterial cultures were obtained from nasopharyngeal swabs collected at routine visits as well as from middle ear fluids during episodes of AOM. In total, 41 M. catarrhalis isolates obtained from 13 children vaccinated with pneumococcal vaccine and 21 M. catarrhalis isolates obtained from six children vaccinated with a control (hepatitis A or B) vaccine were genotyped using pulsedfield gel electrophoresis (PFGE) as described by Verduin et al. [4]. The results of PFGE analysis are presented as a dendrogram in Fig. 1. As an indication of pathogenic potential, all isolates were also tested for the phenotypic expression of complement resistance using the “culture and spot” test [5]. PFGE analysis of the isolates indicated the presence of four clusters comprising a wide range of genotypes. The high degree of diversity within the M. catarrhalis species has already been documented in several publications [6, 7]. No pattern could be observed between PFGE cluster and vaccination status, or PFGE cluster and the isolation of other (co-colonizing) bacteria. M. catarrhalis PFGE types belonging to different clusters were found to occur within the same patient overtime (e.g. patient 1001), an observation that also held true for PFGE types associated with episodes of AOM (e.g. patient 4025). The vast majority of isolates (56/62) were found to be resistant to the effect of complement in human serum, and there was no difference between the isolation of complement-resistant and complement-sensitive phenotypes between the two vaccinated groups (Fisher’s exact test, P=1). The percentage of complement-resistant M. catarrhalis strains isolated appears to be relatively high compared to some studies involving healthy children (90% vs 30–60% [8], respectively), though other studies have yielded results similar to ours [9]. The percentage of complementresistant isolates could have been influenced by the fact that the children enrolled in the study had previously experienced episodes of AOM disease, possibly resulting in an enhanced immune response (including complementmediated responses) against potential bacterial pathogens. J. P. Hays (*) . K. Eadie . C. M. Verduin . H. Verbrugh . A. van Belkum Department of Medical Microbiology and Infectious Diseases, Erasmus University Medical Center Rotterdam (EMCR), Dr Molewaterplein 40, 3015 GD Rotterdam, The Netherlands e-mail: j.hays@erasmusmc.nl Tel.: +31-10-4633668 Fax: +31-10-4633875