Haemophilus influenzae bacteria. Coloured transmission electron micrograph (TEM) of two Haemophilus influenzae type B bacteria. These are Gram-negative, non-motile, rod-like bacteria, which are commonly found in the human upper respiratory tract. This strain, also known as Hib, is a cause of bacterial meningitis in young children. Meningitis is an inflammation of the connective tissue membranes that line the skull. Before the introduction of a Hib vaccine, it was the commonest cause of meningitis of children under the age of two. Magnification: x18, 000 at 6x7cm size.