For strains Rd and 486, siaP mutants with a deficient TRAP transport system were clearly attenuated, with low or undetectable SN-38 bacterial counts in the middle ear after two days (Figure 4). All middle ears (100%) inoculated with strains 486 and Rd developed high-density infection compared

to the absence of middle ear disease in animals challenged with siaP mutants; 486siaP (0/4 ears culture positive; p = 0.02), RdsiaP (0/4 ears culture positive; p = 0.03). For strain 375, the attenuation was less marked (Figure 4) and not statistically significant for the siaP mutant compared to the wild-type strain (375siaP 3/6 ears culture positive; p = 0.39, but sample for 375 wild type was from only 2 animals). This is possibly due to the low levels of LPS sialylation observed for strain 375. Strain RdnanA which showed enhanced LPS sialylation in vitro was of equivalent virulence to the parent strain in the Selleckchem MK-4827 middle ear of Selleck LDN-193189 the chinchilla (Figure 4) (no statistically significant difference between Rd and RdnanA (4/4 ears culture positive; p = 0.31)). Figure 4 Effect of mutation of siaP , siaR and crp on bacterial counts of H. influenzae strains from the middle ear of chinchillas when compared to wild type strains. Animals were inoculated with between 60 and 100 organisms directly into the middle ear bullae. Each data point represents the average number

of organisms ml-1 of exudate or washings from the middle ear for typically four animals at different times (days) following inoculation. Shown are wild type and isogenic strains for: panel (a), NTHi 486; panel (b), Rd; panel (c), NTHi 375. The lower detection limit Venetoclax price is a bacterial count of 2.00. Sialylation of H. influenzae LPS is adaptive and is subject to complex regulation Sialic acid may be incorporated into LPS or utilized as a source of carbon and nitrogen

for NTHi. In the host, given the context of the complex array of other potential nutrients available to H. influenzae and the two potential fates for Neu5Ac in the bacterium, it is reasonable to assume that sugar utilization in H. influenzae is regulated at the genetic level. The intervening 353 bp between the sets of divergently transcribed sialometabolism genes include the binding sites for the regulatory proteins SiaR and CRP [12]. In our experiments, mutation of siaR showed somewhat different phenotypes dependent upon the strain background. Compared to wild type, the RdsiaR mutant strain showed little difference in LPS phenotype (Figure 2d), but was slightly more susceptible to killing in the serum bactericidal assay following growth in the presence of added exogenous sialic acid (Figure 3a). A reduction of serum resistance of a 486siaR mutant (Figure 3b) compared to the parent strain is consistent with some LPS truncation (Figure 2d), although the reason for this is unknown.