Effect of gamma irradiation on antibacterial activities of chitosan is described. Chitosan was prepared from crab shells via demineralization, deproteinization, decoloration and deacetylation. Chitosan solutions (2%) were prepared in 1% acetic acid and irradiated at 0, 5, 15 and 25 kGy. The degree of deacetylation and viscosity-average molecular weight of the chitosan were determined. Susceptibility tests of E. coli and S. parathyphi against the chitosan were determined. E. coli was more susceptible to lower concentrations of chitosan solutions. Irradiated chitosan in solutions exerted a slightly faster inhibition on both E. coli and S. parathyphi than the unirradiated chitosan solution, but there was no difference observed between irradiated and unirradiated chitosan in solutions after 48 hours of incubation. The degree of susceptibility of both E. coli and S. parathyphi to irradiated chitosan in solutions was not significantly affected by the irradiation dose.
A total of 63 samples including ewe milk, yoghurt and traditional buttermilk were collected from Myaneh and Hashrood (Azarbayjan-e-Sharqi, Iran) and screened for the presence of Lactic Acid Bacteria (LAB). Based on routine cultural characteristic, general morphological and biochemical assay, 77 out of 168 bacterial isolates were identified as LAB. These isolates were examined for the presence of inhibitory activity against other randomly selected LAB isolates. Thirty-three strains showed antagonistic activity against the closely related LAB strains and were further challenged against other gram-positive and gram-negative pathogens including Listeria monocytogenes, Staphylococcus aureus and Salmonella entritidis. Based on their zones of inhibition diameters the isolates showing maximum inhibitory activity against these pathogens were selected for detailed investigations. The selected isolates were identified to species level by 50CHL API system and were challenged to heat, acid and bile salt. Most of the strains were able to survive at different pH ranges, while one strain of Pedicoccus acidilactici and Lactobacillus paracasei were able to tolerate all ranges of pH during 24 h of incubation. In addition, Lactobacillus brevis was found as the most resistant strain being able to resist all concentrates of bile after 4 h. The results indicated the probiotic potential of the isolates, as majority of the selected LAB isolates were capable of resisting high temperatures, acidic pH values and bile concentrations of 0.7%.