PubMed · 13822876
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I FINGER, E A KABAT, A E BEZER, A KIDD. 1960. Agar diffusion studies in the dextran-antidextran system.. https://pubmed.ncbi.nlm.nih.gov/13822876/
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The photodynamic activity of 5,10,15-tris[4-(3-N,N,N-trimethylammoniumpropoxy)phenyl]-20-(4-trifluoromethylphenyl)porphyrin iodide (A3B3+) has been studied in vitro on a typical Gram-negative bacterium Escherichia coli immobilized on agar surfaces. The results obtained for the tricationic A3B3+ porphyrin were compared with those of 5,10,15,20-tetra(4-N,N,N-trimethylammoniumphenyl)porphyrin p-tosylate (TTAP4+), which is a standard active sensitizer established to eradicate E. coli in cellular suspension. The photobleaching of these porphyrins in solution was evaluated by decay in absorbance and in fluorescence. In both cases, a higher photostability was found for A3B3+ than for TTAP4+. Photodynamic inactivation capacities of these sensitizers were analyzed in E. coli cells immobilized on agar surfaces. Small colonies were treated with different amount of sensitizer (0-14 nmol) and irradiated with visible light for 3h. The light source used was either a projector or midday sun. The A3B3+ porphyrin produced a growth delay of E. coli colonies on agar surfaces. Similar result was obtained irradiating only one isolated colony through an optical fiber. Under these conditions, A3B3+ porphyrin shows a high activity to inactivate localized bacterial cells. The higher photodynamic activity of A3B3+ was confirmed by mechanical spreading of the colonies before treatment. This procedure produces complete inactivation of E. coli cells on the agar surface. Therefore, tricationic A3B3+ porphyrin is an interesting sensitizer with potential applications in photodynamic inactivation of bacteria growing as localized foci of infection.
We have developed a modified migration assay system in 96-well plate format which is able to detect resistance to the macrocyclic lactone group of drugs in Haemonchus contortus. The assay involves exposure of infective stage larvae to drug for a 24 h period, then counting the numbers of larvae that are able to migrate through an agar and filter mesh system over a further 48 h. The agar barrier greatly increased the sensitivity of the assay for resistance detection compared to use of filter mesh alone. The assay was able to detect the presence of 10% resistant worms in an otherwise susceptible background. However, the assay was ineffective with Trichostrongylus colubriformis and Ostertagia circumcincta indicating that its usefulness for field monitoring will be restricted to situations where H. contortus is of most significance. A small-scale drug screening exercise showed that the assay identifies some anthelmintic activities distinct from those identified by larval development assays. The assay therefore also has a potential role in drug discovery programmes in screening for new anthelmintics.
The effect of water activity (a(w)) (0.82-0.99) on growth and ochratoxin A (OTA) production by twelve Aspergillus niger aggregate strains, cultured in Czapek Yeast Autolysate agar (CYA) and Yeast Extract Sucrose agar (YES), was studied for an incubation period of 30 days. The strains were selected to include diverse sources, different reported abilities to produce OTA and different ITS-5.8 S rDNA Restriction Fragment Length Polymorphism (RFLP) pattern. They were characterized by Random Amplification of Polymorphic DNA (RAPD) and ITS-5.8 S rDNA and 28 S rDNA (D1/D2) sequencing. Regardless of the a(w) value tested, YES was a better culture medium than CYA for OTA production. The a(w) range for OTA production was narrower than that for growth. OTA was produced from 0.90, 0.92, 0.94 or 0.96 to 0.99 a(w) depending on the strain and the culture medium. The molecular study differentiated strains into two groups which corresponded to the RFLP types N and T although it did not distinguish them by their source of isolation or OTA producing abilities. Our results show that A. niger aggregate strains are able to grow and produce OTA over a wide a(w) range. These results will lead to a better understanding of the contribution of A. niger aggregate in OTA contamination of food and feed.