Search

The method described here allows to classify anaerobic bacteria isolated from clinical specimens in four categories of sensitivity or resistance to 8 antibiotics. Previous experiments using eight reference strains led to choose the pre-reduced Schaedler broth supplemented with hemin, vitamin K1, and 0.07 p. cent agar. For each group of three concentrations of antibiotics, a check sample could confirm the growth of the bacteria without antibiotic. Very few minor discrepancies were observed when the results of the classification in categories were compared to the MIC in Wilkins-Chalgren solid medium as reference method. These discrepancies were related to the inoculum and specially for fast-growing species as Bacteroides fragilis or Clostridium. The use of an inoculum standardized to 0.5 MF for slow-growing species and 0.5 MF diluted hundred fold for fast-growing one confirmed the good correlation between the two methods in a short delay.

The author tested parallely 35 Bacteroides fragilis strains by the agar diffusion method and disk technique. A notable discrepancy appears between these two procedures. No regression line can be constructe and the inhibition diameter measurement is unable to class the strain in "susceptible" or "resistant". A literature review on this theme shows that the dissociation between these two techniques were more frequent with anaerobic strains than aerobic for SMX + TMP as others antibiotics. The MIC determination by an agar dilution is the only able to these studies.