Bacteria have evolved numerous defences against antimicrobial agent and drug resistance in pathogen is on rise. This is due to rapid development of multi-drug resistance, limited anti-bacterial spectrum and adverse effects of available anti-microbial agents. This necessitates the search for new antimicrobials with diverse structures and novel mechanism of action. Flowers are mostly used for ornamental purposes and they are not frequently worked out hence marigold flower was selected for the study. The antimicrobial activity of different solvent (Hexane, Toluene, Ethyl acetate, Acetone, Methanol and Aqueous) extracts of marigold flowers were evaluated by agar well diffusion method against a panel of pathogenic microorganisms. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of acetone extract and its fraction were evaluated. B. cereus and K. pneumonia were the most sensitive organisms to acetone extract and minimum inhibitory concentration (MIC) was 78 µg/ml. Synergistic effect of acetone extract and commercial antibiotics (chloroamphenicol and ceftazidime) against pathogenic bacteria was investigated. The best synergistic activity was with combination of acetone extract and ceftazidime against B. subtilis and P. aeruginosa with FIC indices 0.312 and 0.093 respectively. Only the polar solvent acetone extract showed promising antibacterial and synergistic activity. These results indicate that combination between plant extract and the antibiotics could be useful in fighting emerging drug-resistant microorganisms and choice of the solvent plays a prominent role in evaluating antimicrobial activity of medicinal plants. Flowers can be taken as an alternative source of antimicrobial agent against the human pathogens.

Some new dihydro pyrimidinone and pyrimidinethione compounds have been synthesized and their antibacterial activities have been studied in dimethyl formamide and dimethyl sulphoxide against some Gram positive and Gram negative bacteria. For this, Agar well diffusion method is used. It is observed that inhibition depends on solvent, bacterial strain, nature and position of substitution in a compound. When the same substitution is attached to different moieties its effect on bacterial strains changes in different solvents.