Morphological and biochemical variations of Haemophilus influenzae type b induced by pH and temperature changes

Haemophilus influenzae type b ATCC 10211 was cultured at different temperatures (25 degrees C-49 degrees C) and pH values (5.7-8.7) either in liquid or semisolid medium. Morphological variations of individual cells were noted by optical microscopy depending upon the conditions of growth. At higher temperatures filaments were produced whereby the length of individual cells increased compared to cultures grown at 37 degrees C. Filaments were also observed at lower pH values. Culture conditions also affected colonial morphology. At low pH values colonies had an enhanced lobulated contour and were more wrinkly and rougher than at higher pH. The changes in cellular and colonial morphology were correlated with distinct outer membrane protein profiles. The changes in temperature and pH did not affect identification of the microorganism by the API system.