Chemical investigation of the methanolic extract of pomegranate fruit following antibacterial activity directed isolation led to the isolation of pelargonidin-3-galactose, cyanidin-3-glucose, gallic acid, quercetin, and myricetin. All these compounds exhibited substantial activity against species of corynebacteria, staphylococci, streptococci, Bacillus subtilis, Shigella, Salmonella, Vibrio cholera, and Escherichia coli. However, all these compounds were more active against Gram-positive species. On comparing the activity of all the isolated pure compounds, it was found that gallic acid showed the highest antibacterial activity against all the tested sensitive strains and the activity of the remaining pure compounds was almost same due to the structural similarities of the compounds. The reason for antibacterial activity of all pure compounds was attributed to their phenolic structure.

The chemical investigation of the ethanolic extract of the root bark of Onosma hispidum following antibacterial activity directed isolation led to the isolation of 4-hydroxy-3-methoxy cinnamic acid (ferulic acid) and 4-hydroxy-3-methoxy benzoic acid (vanillic acid) which have been reported for the first time in this species. In addition to these compounds, the crude ethanolic extract and methanol fraction exhibited substantial bioactivity against species of corynebacteria, enterococci, staphylococci and streptococci. Ferulic acid was found more bioactive (being relatively more hydrophobic) compared to vanillic acid.

Pseudomonas aeruginosa, in spite of being a ubiquitous organism (as it is found in soil, water, and humans), is also an opportunistic pathogen. In order to maintain its diversity in the community, it produces various toxic proteins, known as, bacteriocins. In the present study, pyocin SA189, which is a bacteriocin produced by P. aeruginosa SA189 (isolated from a clinical sample) was characterized. P. aeruginosa SA189, as identified by the conventional and 16S rRNA gene amplification, produced pyocin SA189 of molecular weight of 66 k Da. The pyocin showed antimicrobial activity against several clinically relevant Gram-positive and Gram-negative bacteria and was substantially stable for wide ranges of temperature and pH. Furthermore, the pyocin also retained its biological activity upon treatment with metal ions, organic solvents, and various proteolytic and lipolytic enzymes. The data from the growth kinetics indicated that the maximum bacteriocin production occurred in the late log phase. Overall, our results signify the potential of pyocin SA189 as a bio-control agent.

Staphylococcus aureus AB201, a clinical isolate from wound pus, produced a bacteriocin‐like inhibitory substance termed as Bac201 that exhibited a broad‐spectrum activity against both gram‐positive as well as gram‐negative bacteria. Among gram‐negative bacteria it was active against Neisseria meningitidis and Acinetobacter calcoaceticus both being gram‐negative cocci. Inhibition due to the effect of organic acids, hydrogen peroxide, or bacteriophages was excluded. This inhibitory substance could not be induced or eluted. It was partially purified to 80% saturation by ammonium sulfate precipitation resulting in maximum specific activity of 829 AU/mg (25‐fold increase). Proteolytic enzymes rapidly inactivated the antagonistic activity of the partially purified material, whereas glycolytic and lipolytic enzymes had no effect. It remained stable in the presence of mild organic solvents. It could be stored at —20 °C without loss of activity, stable at 60 °C and 80°C for 30 min, 100 °C for 20 min and autoclaving temperature (121 °C for 15 min), and exhibited activity within a wide range of pH (2.5—10). Bac201 had an estimated Mr of 41kDa, as indicated by activity detection after SDS‐PAGE. Temperature‐mediated (44 °C) plasmid curing studies suggested linkage of bacteriocin production to a 4.8 MDa plasmid. The Bac201 was bactericidal rather than bacteriolytic.

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