Isolation of antibacterial protein from Lactobacillus spp. and preparation of probiotic curd.

The study was aimed to isolate antagonistic lactobacilli and the molecules responsible for their antagonistic ability from curd. Preparation of probiotic curd and the ability of the selected lactobacilli to suppress the pathogen therein was also assessed. All the 116 isolates were identified as Lactobacillus spp. based on morphological, biochemical and curdling assays. Five of these lactobacilli (Lb-17, Lb-33, Lb-108, Lb-112, and Lb-N3) were found most promising to inhibit all test pathogens (Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae, Salmonella typhi and Shigella sonnei). The cell-free culture supernatants of these five lactobacilli were recorded as thermo-tolerant when subjected to heat treatment at 100 °C for 20 min. The loss in the activity after protease treatment indicated the proteinaceous nature of the antimicrobial molecule present in the culture supernatants. Active protein (19 kDa) produced by lactobacilli was confirmed by SDS-PAGE followed by agar-overlay method. Antibiotic sensitivity assay revealed that the selected Lactobacillus spp. isolates were resistant to methicillin and vancomycin. Probiotic curd prepared by using Lb-108 and Lb-N3 was found to be superior to rest of the three isolates based on organoleptic tests and shelf-life. Complete inhibition of all the test pathogens in curd was shown by Lb-108 and Lb-N3. Inhibition spectrum, production of thermostable protein and preparation of quality curd suggest Lb-108 and Lb-N3 as promising candidates to prepare probiotic curd.

Effect of fungicides on growth and on DNA, RNA and protein anabolism of a Rhizobium sp.

Eleven fungicides were examined for their effect on the growth and anabolism of Rhizobium sp. in pure culture. Of these, only 4 were found to inhibit growth of rhizobia at a concentration as low as 10 micrograms/ml. Growth inhibition by these fungicides appeared to be primarily due to inhibition of respiration, although thiophanate and anilazine also affected DNA and RNA synthesis, respectively. Inhibition is, however, transitory and the bacterium has the ability to overcome this initial inhibition without mutation.

Effect of anilazine on growth, respiration and enzyme activity of Escherichia coli.

The effect of anilazine on growth, respiration and enzyme activity of E. coli has been studied. Anilazine delays the growth of E. coli by prolonging the lag period. It inhibits glucose oxidation by 60% and succinate oxidation by 100%. It also inhibits in vitro succinic dehydrogenase activity. It seems that the inhibition of E. coli by anilazine is because of inhibition of respiratory enzymes.