Antibiotic assays principles and precautions

Detection of Saccharomyces cerevisiae by silver nanoparticles sensitized with various lectins

Anisotropic silver nanoparticles sensitized by various lectins were applied for detection of yeast (Saccharomyces cerevisiae) which was used as a model of fungal cells. It was shown that high concentrations of yeast cells have stabilized silver nanoparticles, preventing their aggregation in the presence of NaCl whereas at low concentrations of cells, the salt has induced aggregation of nanoparticles with drastic changes in optical spectra. These changes depend on cell concentration and permit the detection of cells in the range from 3.2 × 103 to 7 × 107 cell per ml. This approach was used for the determination of these cells in urine and its applicability was demonstrated.

Virgicin, a novel lanthipeptide from Virgibacillus sp. strain AK90 exhibits inhibitory activity against Gram-positive bacteria

There is a significant increase in the discovery of new antimicrobial compounds in recent past to combat drug resistant pathogens. Members of the genus Bacillus and related genera have been screened extensively due to their ability to produce wide range of antimicrobial compounds. In this study, we have isolated and characterized a new antimicrobial peptide from a marine bacterium identified as Virgibacillus species. The low molecular mass and stability of the antimicrobial substance pointed towards the bacteriocinogenic nature of the compound. The RAST analysis of genome sequence showed presence of a putative bacteriocin biosynthetic cluster containing genes necessary for synthesis of a lanthipeptide. Translated amino acid sequence of mature C-terminal propeptide showed identity with salivaricin A (52.2%) and lacticin A (33.3%). Accordingly, the mass (2417 Da) obtained by MALDI analysis was in agreement with posttranslational modifications of the leader peptide to yield three methyl lanthionine rings and a disulfide bond between two free cysteine residues. The lanthipeptide was named as virgicin, which selectively inhibited the growth of Gram-positive bacteria and biofilm formation by Enterococcus faecalis. Inhibition of biofilm formation by E. faecalis was also observed in in vitro model experiments using hydroxyapatite discs. Thus, virgicin appears to be a promising new bacteriocin to control oral biofilm formation by selective pathogens.

Identification of small molecule inhibitors against SecA of Candidatus Liberibacter asiaticus by structure based design

Huanglongbing is the most devastating disease of citrus caused by Candidatus Liberibacter asiaticus (Las). In the present study, we report the discovery of novel small molecule inhibitors against SecA ATPase of Las by using structure based design methods. We built the homology model of SecA protein structure of Las based on the SecA of Escherichia coli. The model was used for in-silico screening of commercially available compounds from ZINC database. Using the glide flexible molecular docking method, twenty structures were chosen for in vitro studies. Five compounds were found to inhibit the ATPase activity of SecA of Las at nano molar concentrations and showed antimicrobial activities against Agrobacterium tumefaciens with MBC ranging from 128 to 256 μg/mL. These compounds appear to be suitable as lead compounds for further development of antimicrobial compounds against Las.

Rapid method for detection and detoxification of heavy metal ions in water environments using phytochelation

Phytochelatins (PCs, (gammaGlu-Cys)n-Gly (n = 2-11)) are produced by higher plants, algae, and some fungi in response to heavy metal ion exposure. A rapid and convenient method for quantifying heavy metal ion concentrations in water environments was developed using a chemically synthesized PC as a mediator. The chelating ability of the PC and quantification of the thiol group were utilized to measure heavy metal ions at low concentrations. The method requires only ten minutes for measurement and only 1 ml of a liquid sample. A range of homogeneous PCs (n = 4-7) were chemically synthesized using a peptide synthesizer. These, especially PC7, exhibited higher sensitivity and consistency of measurement than the native PC from Silene cucubalus, which produced a mixture of PC2, PC3, and PC4. Detoxification of heavy metal ions in vitro by PC was also investigated. Using the paper disc method, the cell growth inhibition zone caused by cadmium ion against Salmonella typhimurium TA1538 was significantly decreased by addition of PC. Furthermore, at the minimum inhibitory concentration of cadmium ion (200 microM) in a nutrient broth culture of S. typhimurium, cell growth was almost completely recovered by addition of PC to the medium.

Therapeutic treatment of New Zealand mouse disease by a limited number of anti-idiotypic antibodies conjugated with neocarzinostatin

-81 and NE-1 idiotypes (Id) of human nephritogenic anti-DNA antibodies are interspecies Id expressed also in NZB/W F1 mice. We tried to manipulate the synthesis of spontaneously occurring anti-DNA antibody using monoclonal anti-Id antibodies (D1E2 and 1F5) conjugated with a cytotoxic agent, neocarzinostatin (NCS). In vivo administration of anti-Id antibodies conjugated with NCS brought about an improvement in the survival rate of female NZB/W F1 mice. It also caused a retardation of development of lupus nephritis and decreased the numbers of anti-DNA-producing cells. The suppression of anti-DNA antibody synthesis was specific and Id-mediated. The results indicate that the use of a limited number of anti-Id antibodies in combination with a cytotoxic agent may be applicable therapeutically to autoimmune diseases.

Automated system for analytical microbiology V: calibration lines for antibiotics

The accuracy of an automated system for the microbiological assay of antibiotics was increased by improvement attendant to connection to an on-line computer. The system was used to investigate the suitability of four forms of interpolation formulas by assaying for chlortetracycline and erythromycin. The calibration lines were prepared as point-to-point straight-line approximations and as cubic equations. Cubic equations through four calibration points were preferred. Since the automated system was a four-channel instrument, a separate response line was prepared for each channel. Combining the four response lines into one could substantially degrade the accuracy and precision of assays. A new general equation relating the response of the test organism to concentrations of active materials was used to account for factors in addition to the antibiotic upon the dose-response line. Some of these factors were: diluents, growth substances, relative proportions of mixed antibiotics, pH and buffer capacities of the sample solution and assay broth, salts, and organic compounds in samples and not in standard solutions. The equation was used to show under what conditions the dose-response lines of mixtures and single-component antibiotics could be the same. It could also account for the nonspecific nature of turbidimetric assays. The equation showed assay biases to be caused not by differences in composition of antibiotics in standards and samples but by differences in other substances affecting growth of the test organism. A new dose-response line applicable to assays using Klebsiella pneumoniae was described.