Broth Agar Dilution Methods Research Articles

Antibacterial activity of iron oxide nanoparticles synthesized by co-precipitation technology against Bacillus cereus and Klebsiella pneumoniae

Abstract The present study investigates the synthesis and characterization of iron oxide nanoparticles (Fe3O4-NPs) for their antibacterial potential against Bacillus cereus and Klebsiella pneumonia by modified disc diffusion and broth agar dilution methods. DLS and XRD results revealed the average size of synthesized Fe3O4-NPs as 24 nm while XPS measurement exhibited the spin-orbit peak of Fe 2p3/2 binding energy at 511 eV. Fe3O4-NPs inhibited the growth of K. pneumoniae and B. cereus in both liquid and soild agar media, and displayed 26 mm and 22 mm zone of inhibitions, respectively. MIC of Fe3O4-NPs was found to be 5 μg/mL against these strains. However, MBC for these strains was observed at 40 μg/mL concentration of Fe3O4-NPs for exhibiting 40–50% loss in viable bacterial cells and 80 μg/mL concentration of Fe3O4-NPs acted as bactericidal for causing 90–99% loss in viability. Hence, these nanoparticles can be explored for their additional antimicrobial and biomedical applications.

Isolation and Identification of Chromium (VI)-Resistant Bacteria From Soltan Abad River Sediments (Shiraz-Iran)

Background: Chromium (Cr) is an important heavy metal widely used in industries. It is one of the seventeen chemicals with the highest danger to human health according to the United States environmental protection agency (USEPA). Objectives: The aim of this study was to isolate and identify Cr (VI)-resistant bacteria from Soltan Abad River sediments (Shiraz-Iran) and evaluate their potential for the detoxification of Cr (VI) to Cr (III) under environmental conditions. Materials and Methods: Bacterial isolates were identified on the basis of colony morphology, Gram staining, and biochemical tests using standard microbiological methods. The minimum inhibitory concentrations (MICs) of chromium were determined by the broth agar dilution method. Cr (VI) reduction assay was determined by measuring the absorbance of the purple complex of Cr (VI) with 1,5-diphenylcarbazide. The growth of Cr (VI)-resistant bacteria was determined at different concentrations of Cr (VI). Finally, the effects of temperature and pH on the growth of selected bacteria and Cr (VI) reduction were investigated using an Luria-Bertani (LB) medium containing 50 mg/L Cr (VI). Results: The results indicated that Pseudomonas aeruginosa and Serratia marcescens were the most resistant bacteria with MICs of 200 and 150 mg/L, respectively. Both bacteria completely reduced 25 and 50 mg/L of Cr (VI) in 36 hours and 48 hours, respectively. The growth rate of both bacteria decreased with increases in the Cr (VI) concentration, and the chromate reduction was directly correlated with the growth of the bacteria. These bacteria were capable of reducing Cr (VI) at a wide range of temperatures (25 to 45°C) and pH levels (5 to 9). The optimum medium conditions for Cr (VI) reduction and the growth of the isolates were temperatures between 30 and 40°C and a pH of 7.0 to 8.0. Conclusions: P. aeruginosa and S. marcescens can be good candidates for the detoxification of Cr (VI) in Soltan Abad River.