A Microbiological Method for the Assay of Subtilin

Introducing Larger plate and Optimum Distribution Pattern in Microbiological assay

First, clinical sample antibiotic assay process. 1966, Appl. Microbiol. 14:2:170–177. This modified agar-disks diffusion experiment employs big glass plates to enable 81 replications per plate. With an agar punch, more than agar disks may be made fast. The savings in zone of inhibition (zoi) from high repeated concentrations of diverse antibiotics with big plates and agar-disks makes it economically possible to employ pooled any antibiotic concentrate. Methods for creating disk diffusion agar and inhibiting bacterial susceptibility degradation are provided. Preparing and maintaining assay organisms is described. Instead of diluting antibiotic tablets to a small range at various concentrations to spread the agar well, they are tested immediately to avoid contamination at the tested concentrations. This is conceivable owing to antibiotic mobility (dilution) and curvilinear computations between area and antibiotic concentrations. This approach has been adapted to many antibiotics. With this technology, vast numbers of antibiotic disks may be tested quickly and accurately. Solid media can be used for antimicrobial susceptibility testing. Solids tests are straightforward and affordable, but they aren't quantitative. Antimicrobial agent diffusion may impair the accuracy of plate-based tests. After applying the above, we evaluated this assumption using the "Eight Queens Puzzle Model" of antibiotic dispersion and a disc diffusion test to estimate the connection between agar depth and area of inhibition and to determine the ideal agar depth. Our studies with agar-diffusion in plates and agar thickness demonstrated that this model describes antibiotic zoi sizes accurately. However, linear regression to explain the link between agar thickness and growth inhibition zone for Staphylococcus aureus and Escherichia coli treated with various antibiotic discs, three groups, the first group (erythromycin) emerged-zone equal sizes for both bacteria. Both bacteria were susceptible to gentamicin and ceftriaxone. Ciprofloxacin's three-group model fit best. Streptomycin's residual deviation was the same for both bacteria. The concentration dependency in the streptomycin group was greater than linear, which may imply a range of low susceptibility rather than a single cut-off dose.

Molecular mechanism of target recognition by subtilin, a class I lanthionine antibiotic

The increasing resistance of human pathogens to conventional antibiotics presents a growing threat to the chemotherapeutic management of infectious diseases. The lanthionine antibiotics, still unused as therapeutic agents, have recently attracted significant scientific interest as models for targeting and management of bacterial infections. We investigated the action of one member of this class, subtilin, which permeabilizes lipid membranes in a lipid II-dependent manner and binds bactoprenyl pyrophosphate, akin to nisin. The role the C and N termini play in target recognition was investigated in vivo and in vitro by using the natural N-terminally succinylated subtilin as well as enzymatically truncated subtilin variants. Fluorescence dequenching experiments show that subtilin induces leakage in membranes in a lipid II-dependent manner and that N-succinylated subtilin is roughly 75-fold less active. Solid-state nuclear magnetic resonance was used to show that subtilin forms complexes with membrane isoprenyl pyrophosphates. Activity assays in vivo show that the N terminus of subtilin plays a critical role in its activity. Succinylation of the N terminus resulted in a 20-fold decrease in its activity, whereas deletion of N-terminal Trp abolished activity altogether.