Minimum inhibitory concentration of active crude extracts
were determined by broth microdilution method as recom-
mended by National Committee for Clinical Laboratories
Standards [10]. The tests were performed in 96 wells mi-
crotiter plates, twofold dilutions of all extracts and standard
antibiotic were made in Muller-Hinton Broth (MHB) rang-
ing from 1 to 512 μg/ml. Each inoculum was prepared in the
same medium at a density adjusted to a 25% transmittance
turbidity standard (108 cfu/ml) and diluted to 1:100 for the
assay. After inoculation, each well contained approximately
5 × 105 cfu/ml. The fi nal volume in the wells was 200 μl.
After 24 hrs of incubation at 37°C, the calculated amount of
nitrogen dried cyanobacterial material present in the most
diluted extract that inhibit a visible growth was defi ned as
MIC.