Browsing by Subject "384-well plate"

Background: Antibiotics have been an important factor in the dramatic decrease of infectious disease mortality in the 20th century. Bacteria are, however, very quick to respond to the changes in their environment because of their short life cycle. Thus, the development of bacterial antibiotic resistance is a natural consequence of the enormous worldwide antibiotic use. The current situation is that the antibiotic resistance develops faster than novel antibiotics are found and developed. The three main resistance strategies of Gram-negative bacteria are: modification of the antibiotic target, enzymatic inactivation of the antibiotic and reduce of the intracellular antibiotic concentration by changing the function of the outer membrane. To decrease the intracellular antibiotic concentration bacteria use efflux pumps. RND efflux pumps are the most important family of efflux pumps regarding antibiotic resistance. They typically function as a part of a tripartite structure which allows the efflux of antibiotics to the extracellular space. Multiple inhibitors have been developed against RND efflux pumps but none has reached the clinical stage of drug development. Objectives: Development and testing of a 384-well plate method for screening efflux pump inhibitors for E. coli (BAA1161) efflux pumps. Methods: Verifying that the absorbance measurement is a sensitive enough method for measuring the bacterial (BAA1161) growth in 384-well plate format. The antibiotic chosen to be used in the screening method was piperacillin and the positive control efflux pump inhibitor was mefloquine. Determining the minimum growth inhibiting concentrations (MICs) of piperacillin and mefloquine in 96- and 384-well plate formats. Verification of the synergistic growth inhibitory effect of piperacillin and mefloquine with the checkerboard method in 96- and 384-well plate formats. Determining the positional effect in the 384-well plate. Determining the highest DMSO concentration without effect on the growth of BAA1161. Screening of 126 natural compounds in 384-well plates to test the developed method. Screening was done in quadruplicates based on the growth inhibitory effect of the natural compounds when combined with piperacillin. Dose-response assay was conducted in combination with and without piperacillin with the compounds that showed growth inhibiting effect during screening. Results and discussion: Absorbance measurement was sensitive enough method for measuring the BAA1161 growth in the 384-well plate. MIC value of mefloquine was 32 μg/ml in both plate formats. Piperacillin’s MIC was 1024 μg/ml in the 96-well plate, but on the 384-well plate there was variation in the MIC. Piperacillin and mefloquine showed synergistic effect on BAA1161 growth inhibition in the checkerboard assays. Positional effect could not be determined, because of the variation in the BAA1161 growth inhibition effect of piperacillin. This randomly occurring phenomenon were piperacillin inhibited BAA1161 growth completely or almost completely with sub-MIC concentration was encountered in all the subsequent experiments in the 384-well plate format. One possible reason for this phenomenon, occuring in the 384-well plate format, could be piperacillin heteroresistance of BAA1161 strain. In the test screen, four compounds, which all included gallic acid ester, showed promising activity. These compounds were: epigallocatechin gallate, hamamelitannin, isopropyl gallate and octyl gallate. In the dose-response assay, hamamelitannin’s and octyl gallate’s effect was synergistic with piperacillin. Conclusions: The developed method can be used to screen novel efflux pump inhibitors. However, to increase the reliability of the method, further optimization is required to eliminate the variability in the effect of piperacillin. When plate format of a method is changed, factors which could affect the functionality of the method in the new format should be carefully assessed. Based on the test screed, gallic acid esters are interesting compounds which combined effects with antibiotics should be studied in the future experiments.