The difference was due to a single point mutation in the capsule gene cpsE. The resulting loss of capsule expression had clear consequences resulting in increased bacterial

growth, adherence to epithelial cells and competence for genetic transformation. We speculate that the mutation occurred in vivo because the isolate contained an approximately 1:1 ratio of the encapsulated and nonencapsulated BGB324 clinical trial phenotypes. This is unlikely to have been achieved during the brief single laboratory culture before freezing the sample. We therefore conclude that the original colony derived directly from the patient contained a mixture of the encapsulated and nonencapsulated phenotypes. Mutations in cpsE have been shown previously to lead to loss of capsule expression in clinical isolates. In 2012, Melchiorre et al., reported two pneumococcal isolates from patients with Trichostatin A manufacturer bacteraemic pneumonia. These isolates

were nonencapsulated but with capsule operons very similar to those of serotype 7F strains. The isolates had two distinct point mutations in cpsE both resulting in premature termination of transcription, CpsE which was truncated at the C terminus and loss of encapsulation in these two strains [62]. CpsE is the initial glycosyltransferase responsible for the addition of activated glucose-phosphate to the lipid carrier in the bacterial membrane [36-40]. Laboratory-generated cpsE knock-out mutants are also nonencapsulated [12]. Here it appears that an encapsulated and nonencapsulated phenotype can co-exist in the nasopharynx. It is also the first time a naturally-occurring mutation in cpsE leading to loss of capsule expression has been described in a PLEKHB2 serotype 18C strain. Unlike the SNP described by Melchiorre et al., the SNP described here does not result in a premature stop

codon but rather an amino acid change from arginine to glycine. In addition, the location of the SNP differs from those described previously [34,35,62]. Our data suggest that the amino acid at position 379 in the cytoplasmic C terminal region of CpsE is critical for the function of the protein and therefore polysaccharide capsule production. cpsE is the first serotype specific gene following the conserved genes cpsA to cpsD [14,15]. However, there is high sequence similarity of cpsE gene throughout the serotypes [12,37-41,63,64] which raises the possibility that SNPs in cpsE may be a more general phenomenon to control capsule expression in other serotypes. This mechanism seems to be irreversible in contrast to the previously described mechanism of loss of capsule expression by spontaneous sequence duplication in the capsule operon [29,30].