In agreement with data presented here, Takamatsu et al. showed that CC1 isolates contained all srt genes, whereas CC29 isolates lacked srtBCD genes [34]. However, none of our serotype 9 isolates contained the srtBCD gene cluster, whereas this cluster was detected in a Japanese serotype 9 isolate [34]. This could imply geographical variation. Moreover, the

revs gene is absent from all cluster B isolates, with the exception of cluster B5 isolates. This regulator influences expression of putative virulence factors [35]. Therefore, lack of revs might affect virulence of isolates. The IgA1 protease gene was found to be absent in all serotype 9 isolates, and displayed extensive sequence variation in serotype 7 isolates. All serotype 2 isolates including the avirulent isolates contained the IgA1 protease gene. Zhang et al. showed that most BGB324 research buy pathogenic serotype 2 isolates contained DNA/RNA Synthesis inhibitor the IgA1 protease gene, whereas the gene was sparsely found in non-invasive serotype 2 isolates [36]. In the latter study mainly isolates obtained in China were used. Sequence variation among isolates belonging to cluster B was observed for other putative virulence genes as well, like ofs, glnA, fbps and apuA. The ofs gene was highly conserved among virulent serotype

1 and 2 isolates but showed extensive sequence diversity in avirulent serotype 2 and serotype 7 isolates, as was also described by Takamatsu et al [15]. Interestingly, at least two of the ofs positive serotype 7 strains do not express OFS in vitro, as shown in the serum opacification assay [37]. This suggests the presence of silent ofs genes. A silent epf gene was present in isolates in cluster B3. Two of the B3 isolates (22083R1 and 8186) expressed the enlarged version of MRP, but none of the probes used for the CGH hybridized to the mrp gene, suggesting extensive Fenbendazole sequence variation exists between different serotype 9 isolates. The presence of a mrp gene in the two isolates was confirmed

by PCR analysis (data not shown). Serotype 9 isolates were distributed among 2 virulence clusters, V6 and V7 that differed considerably in their distribution of putative virulence genes. This suggests differences in virulence exist among serotype 9 isolates that were not identified in our experimental infection model. Avirulent MRP-EF- serotype 2 isolates clustered together with serotype 7 isolates both by CGH as well as by MLST. Such a clustering is in agreement with previous studies [24, 25]. The clustering strongly suggests similarity in genetic background between the isolates and could suggest that the avirulent serotype 2 isolates originated from serotype 7 isolates after the exchange of the capsular genes. Capsular exchange has been described for other streptococci like GBS [38] and Streptococcus pneumonia [39].