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Identified virulence factors of Haemophilus: Antiphagocytosis


Capsule  


View the legend IS1016-V5 IS1016-bexA deletion bexB bexC bexD bsc1 bsc2 bsc3 bsc4 hcsA hcsB orf3 IS1016-V2 bexA bexB bexC bexC bexD bsc1 bsc2 bsc3 bsc4 hscA hscB orf3 IS1016-V2
Keywords: Antiphagocytosis;
Characteristics:
H.influenzae can express one or none of six antigenically distinct polysacchaide capsules, designated a through f.
Bacteria expressing the type b capsule polyribosyl ribitol phosphate (PRP) account for the overwhelming majority of invasive disease isolates.
The most systemic isolates express the type b capsule, whereas most respiratory tract isolates are uncapsulated (referred to as non-typable).
Structure features:
The cap loci for all serotypes consists of functionally unique regions I, II, and III, Regions I and III are common to all six capsular types. Region I genes (bexABCD) code for an ATP-driven capsule export apparatus. Region II contains serotype-specific biosynthesis genes. Region III genes appear to be involved in capsule postpolymerization steps.
The cap locus is flanked by IS1016, which means that recombination in the cap locus can result in amplification as well as loss of capsule genes.
The majority of cap loci in type b strains contain a partial duplication. One copy had lost approximately 1.2kb of DNA, including a substantial part of bexA gene.
Functions:
Protecting the organism from phagocytosis and the bactericidal activity of complement.
References:
Tang CM, et al., 2001. Pathogenesis of Haemophilus influenzae Infections. In Groisman EA (ed.), Principles of Bacterial pathogenesis. Academic Press. San Diego, Calif. pp. 675-716.
Noel GJ, et al., 1996. Effect of amplification of the Cap b locus on complement-mediated bacteriolysis and opsonization of type b Haemophilus influenzae. Infect. Immun. 64(11):4769-4775.
Ogilvie C, et al., 2001. Capsulation loci of non-serotype b encapsulated Haemophilus influenzae. J. Infect. Dis. 184(2):144-149.
Satola SW, et al., 2003. Complete sequence of the cap locus of Haemophilus influenzae serotype b and nonencapsulated b capsule-negative variants. Infect. Immun. 71(6):3639-3644.








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