Surface structures and adherence properties of diverse strains of Haemophilus influenzae biogroup aegyptius

Abstract

Haemophilus influenzae biogroup aegyptius is an important cause of conjunctivitis and has recently been associated with Brazilian purpuric fever (BPF), a fulminant systemic disease of children. To gain insight into the bacterial factors involved in the pathogenesis of this disease, we investigated the surface structures and adherence properties of eight different strains of H. influenzae biogroup aegyptius, including both BPF and non-BPF isolates. All eight strains were able to express long peritrichous pili similar to those observed in H. influenzae. As in H. influenzae, piliation correlated with colony binding of human erythrocytes. However, two strains were capable of hemagglutination in the absence of pili; in these strains, hemagglutination was insensitive to protease treatment, suggesting a nonproteinaceous hemagglutinin. All strains possessed short, thin, surface fibers distinct from long pili and demonstrated efficient attachment to cultured human conjunctival cells. Attachment to conjunctival cells occurred independently of long pili or a capacity for hemagglutination.

HadA is an atypical new multifunctional trimeric coiled-coil adhesin ofHaemophilus influenzaebiogroupaegyptius, which promotes entry into host cells

“…Because of the similarity of HadA to TAAs, we investigated its ability to mediate in vitro bacterial adherence and invasion of Chang epithelial cells (human conjunctival cells), which represent an in vitro model to study infection of H. influenzae biogroup aegyptius (St Geme et al, 1991;Farley et al, 1992). In accordance with previous observations (Li et al, 2003), we found H. influenzae biogroup aegyptius strains resistant to genetic manipulation, and our attempts to construct an isogenic BPF hadA mutant were unsuccessful, also following a previously described method (Segada and Lesse, 1997).…”

“…Enhanced attachment to conjunctival cells was demonstrated for BPF clone strain F3031 compared with that of a non-BPF strain, but the reason for this difference remains unknown (Farley et al, 1992). Moreover, in vitro adherence of H. influenzae biogroup aegyptius to conjunctival cells occurred independently of the presence of long pili detected in some strains (St Geme et al, 1991) and of the Hap protein, which is not expressed in BPF clone strains (Kilian et al, 2002), suggesting that other adhesive factors have to be present on the bacterial surface.…”

“…The mechanism and the role of invasion in the pathogenesis of BPF are poorly understood. Although invasion of in vitro cultured epithelial cells by BPF bacteria seems to be occasional and strain-dependent (St Geme et al, 1991;Farley et al, 1992;Li et al, 2003), it is likely to play an important role during BPF disease. Entry of conjunctival cells may serve as an immune escape purpose in addition to facilitating penetration of the epithelial barrier to reach the bloodstream leading to systemic disease.…”

Evolution of the paralogous hap and iga genes in Haemophilus influenzae: evidence for a conserved hap pseudogene associated with microcolony formation in the recently diverged Haemophilus aegyptius and H. influenzae biogroup aegyptius

“…Studies reported by Qui et al (1998) indicated that human lactoferrin is capable of abolishing Hap-mediated adherence of H. influenzae. It is possible that lack of this target for lactoferrin is an advantage for strains of H. aegyptius and H. influenzae biogroup aegyptius, which may have compensated by enhanced expression of surface pili (Weyant et al, 1990;Reid et al, 1996) or other non-pilus adhesin (St Geme et al, 1991). Feavers and Maiden (1998) recently proposed that the loss of expression of porA was one of the steps in the emergence of the gonococcus from a population that is represented today by the meningococcus.…”

“…Nevertheless, a number of phenotypic differences have been demonstrated including an elongated rod shape of H. aegyptius (Pittman and Davis, 1950;Mazloum et al ., 1982), and the two taxa seem to differ with respect to pathogenic potential, although systematic evidence for this assumption is lacking. Since the discovery of BPF, H. influenzae biogroup aegyptius and H. aegyptius have often been treated as synonyms because of their mutual association with conjunctivitis, and the fact that they share a number of phenotypic traits (urease activity, inability to ferment xylose, lack of indole production, and lack of ornithine decarboxylase activity) (Brenner et al ., 1988;Musser and Selander, 1990;St Geme et al ., 1991). However, there is no direct genetic evidence to support the assumption that they are indistinguishable.…”