A hemadsorption method for detection of colonies of Haemophilus influenzae type b expressing fimbriae

Abstract

Although fimbriated variants of Haemophilus influenzae type b have recently been described, cultures of most clinical isolates contain only a small proportion of fimbriated forms. Because colonies of fimbriated and nonfimbriated cells are visually indistinguishable, a rapid, simple method was developed for the identification and quantitation of colonies of fimbriated H influenzae. This procedure, also applicable to other bacteria (for example, Escherichia coli), involves transferring the colonies from agar to nitrocellulose disks and incubating the disks in a suspension of red blood cells. Colonies that contain predominantly fimbriated bacteria bind the red blood cells and appear as red dots on the nitrocellulose. This nitrocellulose hemadsorption method is described, as well as its applicability for determining the proportion of fimbriated cells in a culture, the kinetics of enrichment of fimbriated forms during enrichment procedures, and the transition rate from the nonfimbriated to the fimbriated state.