English: Control of microbial growth via antimicrobial chemotherapy using dilutions assay

Procedures: 1. Prepare five decimal dilutions of a test antibiotic.

2. Test tubes containing 9 ml of nutrient broth (or other broth depending on the test microorganism) should be inoculated with 0.5 ml of the microorganism to be assayed.

3. Each test tube should receive 0.5 ml of the decimal dilution of the antibiotic in such a way as to allow each dilution at least one test tube for evaluation.

4. The test tubes are to be incubated at 37 ^oC for 24h. 5. After incubation, each test tube is to be observed for potential turbidity changes.

6. The minimal bacteriocidal concentration (MBC) is the concentration at which the antibiotic has prevented any change in turbidity of the broth. Subcultivating suspect test tubes on respective agar media with no antibiotic would allow visualization and confirmation.

RESULTS: Lower concentrations of the antibiotic should not be able to completely prevent microbial growth of the test microorganism. The smallest concentration where the antibiotic has prevented any growth is dubbed the minimal bacteriocidal concentration (MBC), while the smallest concentration where the antibiotic has achieved inhibited microbial growth via a reduced shift in turbidity compared to a control or a lesser concentration, is dubbed the minimal inhibitory concentration (MIC).

Planned and performed by Sofija Kostandinovska, Institute of Biology, FNSM, Ss. Cyril and Methodius University, Skopje, Macedonia.