Disk diffusion test

The ZOI test, also widely known as the Kirby-Bauer disk diffusion test, is a fast in vitro but semiquantitative test [169], The original purpose of this test was to replace the MIC test for small molecule antibiotic efficacy [169], Soon, this method was adopted and modified to evaluate antimicrobial efficacy of silver and polymeric devices with eluting antimicrobial agents [170], Conunonly used eluting antimicrobial agents are zinc salt/particles [171-173], silver salt/particles [173-177], and chlorhexi-dine [178,179], These antimicrobial agents can be compounded/blended into polyurethanes or coated/adsorbed on polyurethanes. 

Ampicillin residues in cultured fish muscle have been detected by a disk diffusion assay using Bacillus stearothermophilus (ATCC 10149) as the test organism (125). In this method, fish sample was homogenized with phosphate buffer, pH 6.0, and centrifuged. The supernate was heated at 82 C for 2 min, and analyzed according to the AOAC assay including the confirmatory -lactamase step. Recoveries of ampicillin ranged from 99 to 104%, whereas the limit of determination was 0.025-1.00 g/g. This method has also been successfully applied for the determination of amoxicillin residues in catfish muscle (126). 

Newly synthesized compounds 22, 23, 25c-e, 26d and 29e were screened in vitro for their antimicrobial activities against Gram positive bacteria Staphylococcus aureus (NCTC-7447), Bacillus cereus (ATCC-14579) and Gram negative bacteria Serratia marcesens (IMRU-70) and Proteus merabitis (NTCC-289) using the paper disk diffusion method for the antibiotic sensitivity technique [60]. The tested compounds were dissolved in N,N-dimclhylformamidc (DMF) to obtain a 1 mg/mL solution. The inhibition zones of microbial growth produced by different compounds were measured in millimeters at the end of an incubation period of 48 h at 28 °C. DMF alone showed no inhibition zone. 

A short report demonstrated the absence of a reliable correlation between kiUing kinetics and normal laboratory tests for pristinamycin susceptibility testing of some pneumococci (42). Eight selected multiresistant clinical isolates and two reference pristinamycin-resistant Streptococcus pneumoniae strains were studied. Disk diffusion susceptibility and MICs were determined by the agar dilution method, and all clinical isolates appeared to be susceptible to pristinamycin, whereas the two reference strains were not. In contrast, time-kill experiments identified a limited bactericidal effect of pristinamycin in three clinical and both reference strains. These three strains had been classified as pristinamycin-resistant by the Vitek-II system, which uses a kinetic turbidimetric measurement of bacterial growth. Epidemiological information is hindered by the use of highly selected strains for the study. 

Kirby-Bauer Disk-Diffusion Method and Modified Kirby-Bauer Susceptibility Test (a. 15)... 

For antimicrobial assays, there are several common methods employed. Due to its ease of operation, the most common method used is the disk diffusion method, which involves the application of a material onto a filter paper disk, and then the disk is placed onto solid medium previously seeded with the test microorganism of interest. Sometimes, the sample is dissolved in an appropriate solvent before application onto the paper disk. This method is very common in the evaluation of antibiotics and is the method adopted by the National Committee for Clinical Laboratory Standards (NCCLS). The method depends on the aqueous solubility of the antibiotics in order to facilitate diffusion through the solid medium. Essentials oils, however, are generally hydrophobic, do not readily diffuse through an aqueous medium and, therefore, the prevalence of false negatives or reduced activity might then be anticipated. 

TESTING FOR MICROBIAL SENSITIVITY TO ANTIMICROBIAL AGENTS Bacterial strains, even from the same species, may vary widely in sensitivity to antibiotics. Information about the antibiotic sensitivity of the infecting microorganism is important for appropriate drug selection. Various methods are used to assess susceptibility, including disk-diffusion, dilution test, and automated broth dilution. The results are either reported on a semi-quantitative scale i.e., resistant, intermediate, or susceptible) or in terms of the minimal inhibitory concentration (MIC). 

Asperazine (168) showed significant leukemia-selective cytotoxicity in tests on different cell lines using the Corbett-Valeriote soft agar disk diffusion assay [187]. 

Inhibitory Data of Cassia Oil Obtained in the Agar Diffusion Test Disk Size (mm), Inhibition ... 

Inhibitory Data of Ceylon MO Cinnamon Bark Oil Obtained Disk Size (mm), in the Agar Inhibition Diffusion Test... 

Cyclic disulfides have been shown to exhibit a variety of antimicrobial properties (85,88). The compounds 1,2,5,6-tetrathiacyclooctane (29a) and 1,2,5,6,9,10-hexathiacyclododecane (29b) were tested for antimicrobial activity, using a standard disk diffusion assay. The compound (29a) exhibited moderate antimicrobial activity toward Escherichia coli. 

The library of silver-NHC compounds has been greatly expanded due to the contributions of Tacke and coworkers (13a-21) [13-17] and Roland et al. (22a-25b) [18]. Compounds 13a-21 (Figure 6.1), all bearing the acetate ligand, were evaluated for their antimicrobial efficacy against S. aureus and . coli using a qualitative Kirby-Bauer disk-diffusion method. The imidazolium salt precursors, silver acetate, and the vehicle (dimethylsulfoxide) served as controls. The results of the tests were mixed, with a number of compounds having a weak... 

In contrast, agar dilution and broth microdilution methods are able to overcome some of the limitations of the disk diffusion method. Not only are they more convenient for routine antimicrobial susceptibihty testing of bacteria in clinical laboratories, they are capable of drawing quantitative conclusions by determining the MIC values for antimicrobials, as opposed to qualitative data generated by the disk diffusion method (Kim and Kim 2007). 

Another reason for careful interpretation of the disk-diffusion assay is that it is subject to false-positive results that can be misinterpreted as antibiotic activity. For example, physical characteristics of the extract (viscosity, pH, etc.) can generate small zones of growth inhibition when bacteria are inoculated directly onto the surface of the agar plate. In addition, we have observed that some primary metabolites can inhibit growth when tested at high concentrations. It is also possible that simple molecules, or extract degradation products, can exhibit mild antibiotic properties. For these reasons, it is important that replicate extracts are tested and that small zones of inhibition are interpreted with caution. It is also important to clearly state the concentrations tested, even if naturally occurring concentrations are not known, so that activities can be reproduced and evaluated at a later time. 

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