Micromethod for determination of antibacterial capacity in amniotic fluid.

A new method for assessing antibacterial activity in amniotic fluid (AF) is presented. Sample sizes of 100 microliter were incubated at 37 degrees C in an equal amount of growth medium with inoculated bacteria. The quantification of bacterial growth was established by measuring the change in optical density with an automated spectrophotometer. In this study, Escherichia coli, type K 12, was used for inoculation and the bacterial growth was assessed after 6, 18, 30, 42, and 54 hours' incubation. The variation coefficients in intra-assay and interassay measurements were 3.8 and 5.2%, respectively. Shaking of the incubated sample significantly changed the results by increasing the number of viable cells in the most probable number method and decreasing the optical density difference in the spectrophotometric method. Nevertheless, the correlation between the results in both methods was good (r = 0.94, p less than 0.05, and r = 0.98, p less than 0.01, respectively). By filtering the AF sample before incubation, a great deal of antibacterial activity was removed. The reproducibility, simplicity, and rapidity of this spectrophotometric method of assessing antibacterial activity in AF may make it a useful clinical tool.