Nasopharyngeal co-colonization with Staphylococcus aureus and Streptococcus pneumoniae in children is bacterial genotype independent.

Bacterial interference between Staphylococcus aureus and Streptococcus pneumoniae in the nasopharynx has been observed during colonization, which might have important clinical implications for the widespread use of pneumococcal conjugate vaccine in young children. This study aimed to determine whether the capacity of Staph. aureus to compete with Strep. pneumoniae is dependent on bacterial genotype. Demographic and microbiological determinants of carriage of specific genotypes of Staph. aureus in children were also studied. Children (n=3198) were sampled in the nasopharynx to detect carriage of Staph. aureus, Strep. pneumoniae and Neisseria meningitidis. Staph. aureus genotypes and pneumococcal sero- and genotypes were determined. Age, gender, zip code, active smoking and co-colonization with N. meningitidis or Strep. pneumoniae, both vaccine- and non-vaccine types, were not associated with colonization by specific Staph. aureus genotypes. Based on the whole-genome typing data obtained, there was no obvious correlation between staphylococcal and pneumococcal genotypes during co-colonization. Passive smoking showed a significant association (P=0.003) with carriage of a specific Staph. aureus cluster. This study suggests that there are no major differences between Staph. aureus clones (with different disease-invoking potential) in their capacity to compete with Strep. pneumoniae subtypes. Further studies should demonstrate whether differences in bacterial interference are due to more subtle genetic changes.

Identification of DNA sequence variation in Campylobacter jejuni strains associated with the Guillain-Barré syndrome by high-throughput AFLP analysis.

BACKGROUND: Campylobacter jejuni is the predominant cause of antecedent infection in post-infectious neuropathies such as the Guillain-Barré (GBS) and Miller Fisher syndromes (MFS). GBS and MFS are probably induced by molecular mimicry between human gangliosides and bacterial lipo-oligosaccharides (LOS). This study describes a new C. jejuni-specific high-throughput AFLP (htAFLP) approach for detection and identification of DNA polymorphism, in general, and of putative GBS/MFS-markers, in particular. RESULTS: We compared 6 different isolates of the "genome strain" NCTC 11168 obtained from different laboratories. HtAFLP analysis generated approximately 3000 markers per stain, 19 of which were polymorphic. The DNA polymorphisms could not be confirmed by PCR-RFLP analysis, suggesting a baseline level of 0.6% AFLP artefacts. Comparison of NCTC 11168 with 4 GBS-associated strains revealed 23 potentially GBS-specific markers, 17 of which were identified by DNA sequencing. A collection of 27 GBS/MFS-associated and 17 enteritis control strains was analyzed with PCR-RFLP tests based on 11 of these markers. We identified 3 markers, located in the LOS biosynthesis genes cj1136, cj1138 and cj1139c, that were significantly associated with GBS (P = 0.024, P = 0.047 and P < 0.001, respectively). HtAFLP analysis of 13 highly clonal South African GBS/MFS-associated and enteritis control strains did not reveal GBS-specific markers. CONCLUSION: This study shows that bacterial GBS markers are limited in number and located in the LOS biosynthesis genes, which corroborates the current consensus that LOS mimicry may be the prime etiologic determinant of GBS. Furthermore, our results demonstrate that htAFLP, with its high reproducibility and resolution, is an effective technique for the detection and subsequent identification of putative bacterial disease markers.

Natural population dynamics and expansion of pathogenic clones of Staphylococcus aureus.

The population structure of Staphylococcus aureus carried by healthy humans was determined using a large strain collection of nonclinical origin (n = 829). High-throughput amplified fragment length polymorphism (AFLP) analysis revealed 3 major and 2 minor genetic clusters of S. aureus, which were corroborated by multilocus sequence typing. Major AFLP cluster I comprised 44.4% of the carriage isolates and showed additional heterogeneity whereas major AFLP groups II and III presented 2 homogeneous clusters, including 47.3% of all carriage isolates. Coanalysis of invasive S. aureus strains and epidemic methicillin-resistant S. aureus (MRSA) revealed that all major clusters contained invasive and multiresistant isolates. However, clusters and subclusters with overrepresentation of invasive isolates were also identified. Bacteremia in elderly adults, for instance, was caused by a IVa cluster-derived strain significantly more often than by strains from other AFLP clusters. Furthermore, expansion of multiresistant clones or clones associated with skin disease (impetigo) was detected, which suggests that epidemic potential is present in pathogenic strains of S. aureus. In addition, the virulence gene encoding Panton-Valentine leukocidin was significantly enriched in S. aureus strains causing abscesses and arthritis in comparison with the carriage group. We provide evidence that essentially any S. aureus genotype carried by humans can transform into a life-threatening human pathogen but that certain clones are more virulent than others.