Antimicrobial activity of silver nanoparticles is gaining importance due its broad spectrum of targets in cell compared to conventional antimicrobial agents. In this context, silver nanoparticles were synthesized by gamma irradiation-induced reduction method of acrylamide and itaconic acid with irradiation dose up to 70 kGy. Silver nanoparticles were examined by Fourier-transform infrared, scanning electron microscopic images (SEM), and ultraviolet-visible spectrophotometer. The particle size was determined by X-ray diffraction, transmission electron microscopy (TEM), and dynamic light scattering. The antibacterial effect was studied by disk diffusion method against some bacterial pathogenic strains. Silver nanoparticles showed promising activity against Pseudomonas aeruginosa and slightly active against Escherichia coli, methicillin-resistant Staphylococcus aureus, and Klebsiella pneumonia. The bactericidal effect of silver nanoparticles was tested against P. aeruginosa. The killing rate of P. aeruginosa was found to be 90 % of viability at (100 μl/ml) of silver nanoparticles. Exposure of P. aeruginosa cells to silver nanoparticles caused fast loss of 260 nm absorbing materials and release of potassium ions. The TEM and SEM observation showed that silver nanoparticles may destroy the structure of bacterial cell membrane in order to enter the bacterial cell resulting in the leakage of the cytoplasmic component and the eventual death.
Background: Misuse of antibiotics in veterinary medicine has the potential to generate residues in animal derived products, which could contributing to the development of an important health risk either through the exposure to antibiotic residues or the transfer of antibiotic resistance among foodborne pathogens as well. Tetracycline (TE) and eptomycin (ST) are commonly used as antibiotics in the Egyptian animal husbandry. The objective of this study, quick detection of TE and ST in fresh local beef tissue samples using radioimmunoassay Charm II technique, isolation and identification of relevant highly resistant bacterial strains. In addition to investigating the effect of gamma radiation on the susceptibility of such resistant strains to TE and ST. Results: Tetracycline (TE) was detected in all collected samples, while ST was detected in 38.46% (5/13) and 87.5% (7/8) of meat and liver samples, respectively. Fifty-one bacterial isolates were isolated from the tested samples, among them, the highest resistant isolates to TE or ST were identified as Streptococcus thoraltensis, Proteus mirabilis (2 isolates) and E. coli (3 isolates). Among them, the highest D 10-values in phosphate buffer; 0.807 and 0.480; kGy were recorded with S. thoraltensis and E. coli no.3, respectively. Such values increased to record 0.840 and 0.549 kGy, respectively after artificial inoculation into meat, indicating increased resistance to gamma radiation. Gamma radiation at dose 3 kGy increased the susceptibility of S. thoraltensis up to 50% to TE and ST, while the sensitivity of E. coli no.3 reached up 56% to both antibiotics at the same dose. Conclusions: High prevalence of TE in all fresh collected tissue samples suggests an extensively use of TE as antimicrobial in conventional beef production as compared to ST in the Egyptian cows' husbandry. Moreover, irradiation of food from animal origin by gamma radiation could potentially provide protection against resistant strains. In spite of limited samples used in this study, our data could raise the concerns of public health professionals about a withdrawal period before animals slaughtering, and address the importance of gamma radiation to minimize the hazards of foodborne resistant bacteria.
A b s t r a c tGamma irradiation is used on Penicillium cyclopium in order to obtain mutant cells of high L-asparaginase productivity. Using gamma irradiation dose of 4 KGy, P. cyclopium cells yielded L-asparaginase with extracellular enzyme activity of 210.8 ± 3 U/ml, and specific activity of 752.5 ± 1.5 U/mg protein, which are 1.75 and 1.53 times, respectively, the activity of the wild strain. The enzyme was partially purified by 40-60% acetone precipitation. L-asparaginase was immobilized onto Amberlite IR-120 by ionic binding. Both free and immobilized enzymes exhibited maximum activity at pH 8 and 40°C. The immobilization process improved the enzyme thermal stability significantly. The immobilized enzyme remained 100% active at temperatures up to 60°C, while the free asparaginase was less tolerant to high temperatures. The immobilized enzyme was more stable at pH 9.0 for 50 min, retaining 70% of its relative activity. The maximum reaction rate (V max ) and Michaelis-Menten constant (K m ) of the free form were significantly changed after immobilization. The K m value for immobilized L-asparaginase was about 1.3 times higher than that of free enzyme. The ions K + , Ba 2+ and Na + showed stimulatory effect on enzyme activity with percentages of 110%, 109% and 106% respectively. K e y w o r d s: Penicillium cyclopium, Amberlite IR-120, gamma irradiation, ionic binding immobilization, L-asparaginase
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