Fundamental studies are essential for the practice of in vitro antibacterial sensitivity test of antibiotics. In vitro minimum inhibitory concentration (MIC) of ampicillin was tested to study the conditions of selection of proper culture media using 6 standard strains of Staph. aureus, E. coli and Salmonella. Although the results of MIC tests hardly showed disparity among the culture media tested, heart infusion broth medium proved to be the best bacterial growth medium, and trypticase soy agar to be most sensitive in the MIC test. Antibacterial sensitivity was considerably influenced by the pH of the medium and bacterial cell counts. Optimal antibacterial sensitivity was obtained with a culture medium in the pH range of 7.0 to 7.5 and with bacterial cell count of 1×106/ml.
