Detection of Bacteroides fragilis and Bacteroides melaninogenicus by direct immunofluorescence

A new diagnostic kit, which contains a polyvalent antiserum for either Bacteroides fragilis or Bacteroides melaninogenicus, was tested for reliability and specificity on 146 clinical samples of different origin. A correlation between the culture and immunofluorescence was observed for B. fragilis in 87.39% of cases and for B. melaninogenicus in 81.48% of cases. When pure cultures were tested, aerobically as well as anaerobically, false-positive reactions were observed with staphylococci and Clostridium ramosum spores. The well-defined morphology of these bacteria and spores allows for the elimination of any diagnostic error. The method is rapid, and the margin for error is limited. The test gives a semiquantitative idea of the number of bacteroides organisms present in the clinical specimens even in the presence of a mixed flora.