BACKGROUND: In this study, efficacy and consistency of disc diffusion (DD) and agar dilution (AD) methods in determining Helicobacter pylori susceptibility to antibiotics were evaluated using Brucella blood agar (BBA) in both methods and tetrazolium egg yolk agar (TEYA) in AD. METHODS: Twenty H. pylori isolates were tested for susceptibility to nine antibiotics; metronidazole (MTZ), clarithromycin (CLR), amoxicillin (AMX), tetracycline (TET), ofloxacin (OFX), levofloxacin (LVX), ciprofloxacin (CIP), furazolidone (FRZ), and rifampin (RIF). Antibiotics solutions were impregnated into blank paper disks on BBA in the DD method or added to BBA (ADB) or TEYA (ADT) media in the AD method. Suspensions of H. pylori isolates were surface or spot inoculated on solid media. Plates were incubated in CO2 incubator at 37°C for 5-7 days. RESULTS: The highest rate of susceptibility to MTZ (65%) was determined by DD method compared with AD method (ADB: 40%, ADT: 30%). Both methods showed similar CLR (85%) and AMX (100%) susceptibility rates. Susceptibility to remaining antibiotics, determined by DD and ADB/ADT media were in respective order as 95%, 75% / 75% for TET, 100%, 95% / 85% for FRZ, 85%, 85% / 75% for OFX, 90%, 95% / 85% for LVX, 90%, 85% / 85% for CIP, and 100%, 85% / 75% for RIF. CONCLUSION: DD and AD methods showed consistency in determining 161 (89.4%) susceptibility and resistance and inconsistency in determining 19 (10.6%) susceptibility and resistance (P < 0.05). DD is recommended as a cheap and easy method with the efficacy and precision comparable to the AD method in determining H. pylori susceptibility to antibiotics.
The treatment of Escherichia coli infections has been seriously complicated due to the appearance of multidrug-resistant isolates and the rapid distribution of extended-spectrum β-lactamase-producing species. In recent years there has been considerable effort to develop alternative therapies to traditional antibiotics for infection diseases caused by antimicrobial agents. The mechanisms by which antimicrobial compounds induce bacterial damage have been suggested to be interaction with membranes, formation of pores lined by both lipids and peptides, or by a more general “Anionic lipid clustering,” and other specific mechanisms. The major constituents of the lipid bilayer on the outer membrane of E. coli as a Gram-negative bacteria are lipopolysaccharide, zwitterionic core oligosaccharides, saturated fatty acid chains with zwitterionic phospholipid head groups, and lipid A functionalized with anionic phosphate groups. Research findings emphasize the importance of the membrane composition of E. coli in determining the susceptibility to certain antimicrobial agents, such as antimicrobial peptides (AMPs) and successful treatment.
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