Gram-negative (see GRAM'S STAIN), rod-like bacteria. Often found in the respiratory tract, they may be harmless but can be responsible for several diseases. The main pathogenic species of haemophilus is H. influenzae, which may cause severe exacerbations of chronic BRONCHITIS, as well as MENINGITIS, EPIGLOTTITIS, SINUSITIS, and otitis media (see EAR, DISEASES OF). Other species may cause conjunctivitis (see EYE, DISORDERS OF) or CHANCROID. Haemophilus species are sensitive to a wide range of antibiotics, though generally resistant to penicillin. Infants are routinely immunised with Haemophilus B vaccine to prevent meningitis, septicaemia and epiglottitis – all potentially fatal diseases which have almost disappeared in the UK, with the only sufferers being those who are unimmunised or infected with the rarer non type-B organisms.