In a search for the genetic basis for the structural difference between the related Streptococcus pneumoniae capsular serotypes 15B and 15C and for the reported reversible switching between these serotypes, the corresponding capsular polysaccharide synthesis (cps) loci were investigated by keeping in mind that at the structural level, the capsules differ only in O acetylation. The cps locus of a serotype 15B strain was identified, partially PCR amplified with primers based on the related serotype 14 sequence, and sequenced. Sequence analysis revealed, among other open reading frames, an intact open reading frame (designated cps15bM) whose product, at the protein level, exhibited characteristics of previously identified acetyltransferases. Genetic analysis of the corresponding region in a serotype15C strain indicated that the same gene was present but had a premature stop in translation. Closer analysis indicated that the serotype 15B gene contained a short tandem TA repeat consisting of eight TA units. In serotype 15C, this gene contained nine TA units that resulted in a frameshift and a truncated product. Genetic analysis of 17 serotype 15B and 15C clinical isolates revealed a perfect correlation between the serotype and the length of the short tandem repeat in the putative O-acetyltransferase gene. The number of TA repeating units varied between seven and nine in the various isolates. Together, the data strongly suggest that the structural difference between serotypes 15B and 15C is based on variation in the short tandem TA repeat in the O-acetyltransferase gene and that the transition between serotypes is due to slipped-strand mispairing with deletion or insertion of TA units in the cps15bM gene. <<<

Bartonella henselae causes cat scratch disease and the vasculoproliferative disorders bacillary angiomatosis and peliosis hepatis in humans. One of the best known pathogenicity factors of B. henselae is Bartonella adhesin A (BadA), which is modularly constructed, consisting of head, neck/stalk, and membrane anchor domains. BadA is important for the adhesion of B. henselae to extracellular-matrix proteins and endothelial cells (ECs). In this study, we analyzed different B. henselae strains for BadA expression, autoagglutination, fibronectin (Fn) binding, and adhesion to ECs. We found that the B. henselae strains Marseille, ATCC 49882, Freiburg 96BK3 (FR96BK3), FR96BK38, and G-5436 express BadA. Remarkably, BadA expression was lacking in a B. henselae ATCC 49882 variant, in strains ATCC 49793 and Berlin-1, and in the majority of bacteria of strain Berlin-2. Adherence of B. henselae to ECs and Fn reliably correlated with BadA expression. badA was present in all tested strains, although the length of the gene varied significantly due to length variations of the stalk region. Sequencing of the promoter, head, and membrane anchor regions revealed only minor differences that did not correlate with BadA expression, apart from strain Berlin-1, in which a 1-bp deletion led to a frameshift in the head region of BadA. Our data suggest that, apart from the identified genetic modifications (frameshift deletion and recombination), other so-far-unknown regulatory mechanisms influence BadA expression. Because of variations between and within different B. henselae isolates, BadA expression should be analyzed before performing infection experiments with B. henselae. <<<