Importantly, in the chinchilla model of OM, mutation of siaR in strains Rd, 375 and 486 produced strains that were virulent (Figure 4), although
we cannot rule out some difference in bacterial titres during the course of disease. Thus, siaR is not essential for virulence in this model. There is a consensus sequence for CRP binding (TGTGATCAACTTCTCA) within the DNA region intergenic between nanE and siaP [12, 29], consistent with the role of CRP in regulating Neu5Ac uptake genes. Of the mutant strains with crp inactivated, only NTHi 486 displayed any alteration in LPS profile (Figure 2d) and some increased serum sensitivity compared to the parent strain (Figure 3b). Significantly, in vivo in the chinchilla, each of the strains Rdcrp, 375crp and 486crp were virulent (Figure Nivolumab concentration 4). To investigate
in more detail the interdependence Erlotinib of genes involved in sialometabolism, we compared gene expression in wild type and mutant strains following growth in the presence or absence of exogenous Neu5Ac. RT-PCR analysis of total RNA extracted from strain Rd mutated in each of the genes nanA, siaR, nanK, nanE, siaP, siaQM, HI0148 and crp was performed using internal pairs of primers specific for each gene of interest (Table 1) and the levels of expression compared using the RT-PCR amplification product for the housekeeping gene, frdB, as a control between samples. The level of transcript for each sialometabolism gene was generally greater in the siaR mutant background when compared L-gulonolactone oxidase to the wild type strain, although the results proved difficult to quantify (data not shown). This would be consistent with SiaR exerting a regulatory (negative) effect on sialometabolism gene expression, i.e. acting as a repressor . The corresponding change
in expression of multiple genes might suggest some co-regulation or co-dependence. Using primer pairs targeted against the 5′ and 3′ ends of adjacent genes across the region, RT-PCR analysis showed some co-transcripts for most gene pairs across the sialometabolism region (Figure 5). Figure 5 PCR amplification for cDNA of sialometabolism genes from strain Rd showing co-transcripts for adjacent gene pairs. cDNA was made after bacteria were grown in BHI in the presence of sialic acid. RT-PCR products shown are in lane 2, nagA/nagB; lane 3, nagB/nanA; lane 4, nanA/siaR; lane 5, siaR/nanK; lane 6, nanK/nanE; lane 7, siaP/siaQM; lane 8, siaQM/HI0148. Lane 1 shows the 1 kb DNA ladder marker with the 1.6 kb band marked by an arrow. We obtained quantitative data for the changes in the level of expression of representative sialometabolism genes (siaR, nanE, siaP, HI0148) by q-PCR. These data confirmed the key observation from our initial microarray experiment , i.e.