Haemophilus influenzae is a small gram-negative coccobacillus known as one of the major causes of
meningitis,
otitis media,
sinusitis and
epiglottitis, especially in childhood, as well as
infections of the lower respiratory tract,
eye infections and
bacteremia. It has several
virulence factors that play a crucial role in patient inflammatory response. Its
capsule, the adhesion
proteins, pili, the outer
membrane proteins, the
IgA1 protease and, last but not least, the lipooligosaccharide, increase the virulence of H. influenzae by participating actively in the host invasion the host by the microrganism. Some of these factors are used in
vaccine preparations. In the post-
vaccine era, an increase has been noticed in many European countries of invasive
infections caused by non-encapsulated strains of H. influenzae which have a number of
virulence factors, some of which are subject of serious research aiming at creating new
vaccines. Numerous mechanisms of antibiotic resistance in H. influenzae are known which can compromise the empirical treatment of
infections caused by this microorganism. The increasing incidence of resistance to aminopenicillins, induced not only by
enzyme mechanisms but also by a change of their target is turning into a significant problem. Resistance to other
antibiotics such as
macrolides,
tetracyclines,
chloramphenicol,
trimethoprim/sulfamethoxazole, and
fluoroquinolones, commonly used to treat
Haemophilus infections has also been described.