Methods: Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were used to measure the size and shape of NPs. Minimum inhibitory concentrations (MIC) of nano-silver on selected beneficial microbes and Ralstonia solanacearum were measured using the microdilution broth method. The percentage of seed germination was measured under in vitro conditions.
Results: NPs were spherical with a size of 16 ± 6 nm. Nano-silver at 12-40 mg l-1 inhibited the growth of bacteria. Seed application at 40 mg l-1 protected seeds from R. solanacearum and improved the rate of seed germination.
METHODS: B. subtilis was exposed to 5 to 150 μg/mL of ZnO NPs for 24 h. The parameters employed to evaluate the antimicrobial potential of ZnO NPs were the growth inhibitory effect on B. subtilis, the surface interaction of ZnO NPs on the bacterial cell wall, and also the morphological alterations in B. subtilis induced by ZnO NPs.
RESULTS: The results demonstrated a significant (p <0.05) inhibition of ZnO NPs on B. subtilis growth and it was in a dose-dependent manner for all the tested concentrations of ZnO NPs from 5 to 150 μg/mL at 24 h. Fourier transformed infrared (FTIR) spectrum confirmed the involvement of polysaccharides and polypeptides of bacterial cell wall in surface binding of ZnO NPs on bacteria. The scanning electron microscopy (SEM) was used to visualize the morphological changes, B. subtilis illustrated several surface alterations such as distortion of cell membrane, roughening of cell surface, aggregation and bending of cells, as well as, the cell rupture upon interacting with ZnO NPs for 24 h.
CONCLUSION: The results indicated the potential of ZnO NPs to be used as an antibacterial agent against B. subtilis. The findings of the present study might bring insights to incorporate ZnO NPs as an antibacterial agent in the topical applications against the infections caused by B. subtilis.
STUDY DESIGN: The MICs for 135 clinical isolates of N. gonorrhoeae were determined by a modified Kirby-Bauer method recommended by the National Committee for Clinical Laboratory Standards against penicillin, cefuroxime, ceftriaxone, norfloxacin, tetracycline, kanamycin, spectinomycin, and azithromycin. The MIC of azithromycin was determined by both the E-test and agar dilution method. All tests were done simultaneously.
RESULTS: The MIC of azithromycin to all 135 isolates ranged from 0.078 to 0.25 microgram/ml with the agar dilution method and from 0.016 to 0.50 microgram/ml with the E-test. The MIC50 and MIC90 of azithromycin were 0.064 microgram/ml and 0.125 microgram/ml, respectively, by the agar dilution method, whereas they are slightly higher by the E-test method. Seventy-six of the isolates were beta-lactamase producers and 69 were high-level tetracycline-resistant N. gonorrhoeae. There was no difference in the MIC50 and MIC90 of azithromycin in these groups of isolates. The percentage agreement within the acceptable +/-1 log2 dilution difference between MICs obtained by E-test and those obtained by the agar dilution method was 97.8%.
CONCLUSIONS: Azithromycin has a very good in vitro antigonococcal activity, and the E-test is a reliable method to determine the MIC of azithromycin against N. gonorrhoeae.