Table of Contents
What is the disk diffusion test used for?
In diagnostic laboratories, the disk diffusion test is used to determine the susceptibility of clinical isolates of bacteria to different antibiotics.
What is disc diffusion method for antimicrobial activity?
The method consists of placing paper disks saturated with antimicrobial agents on a lawn of bacteria seeded on the surface of an agar medium, incubating the plate overnight, and measuring the presence or absence of a zone of inhibition around the disks (Figure 1).
What is the principle of the agar disc diffusion method?
This method is based on the principle that antibiotic-impregnated disk, placed on agar previously inoculated with the test bacterium, pick-up moisture and the antibiotic diffuse radially outward through the agar medium producing an antibiotic concentration gradient.
Can a antibiotic disc wipe out the entire bacterial lawn?
Since it’s very unlikely that one antibiotic disk will kill all the bacteria on the plate, I suggest you use a method like what Asyed suggested earlier: increasing the number of antibiotic disks on each plate until all the bacteria are killed.
What is the size of antibiotic disc?
Each antibiotic sensitivity disc is 1/4″ diameter. These antibiotic discs are used for bacteria sensitivity testing and allow you to test up to two different bacteria cultures with four different antibiotics.
What does the Zone of inhibition tell you?
The Zone of inhibition is a circular area around the spot of the antibiotic in which the bacteria colonies do not grow. The zone of inhibition can be used to measure the susceptibility of the bacteria to wards the antibiotic.
What does a clear zone of inhibition mean?
After a certain point, its concentration is so low that it can no longer inhibit the growth of the bacterium. Therefore, there is an area around the disks that will be clear against a dense growth (lawn) of the bacterium surrounding it, this zone of clearance is defined as the zone of inhibition.
What do the numbers on an antibiotic disk represent?
Letters on the discs give the identity and concentration in micrograms of the antibiotic in the disc. ATM, aztreonam; C, chloramphenicol; CIP, ciprofloxacin; CN, gentamicin; CT, colistin; DA, clindamycin; E, erythromycin; FOX, cefoxitin; LZD, linezolid; MEM, meropenem; TE, tetracycline; TOB, tobramycin; VA, vancomycin.
Is disk diffusion test accurate?
Across all 115 specimens, the disk diffusion tests produced good categorical agreements, exhibiting concordance of 93.1%, 92.1%, and 90.4% with agar dilution and 93.0%, 92.1%, and 90.4% with Etest®, for CRO, CFX, and CPD, respectively.
What does a big zone of inhibition mean?
Large zones of inhibition indicate that the organism is susceptible, while small or no zone of inhibition indicateresistance. An interpretation of intermediate is given for zones which fall between the accepted cutoffs for the other interpretations.
What is a zone of inhibition and what does it indicate?
zone of inhibition: This is an area of media where bacteria are unable to grow, due to presence of a drug that impedes their growth. minimum inhibitory concentration: This is the lowest concentration of an antimicrobial drug that prevents visible growth of a microorganism after overnight incubation with media.
What is disk diffusion Antimicrobial Susceptibility Testing?
Disk diffusion antimicrobial susceptibility testing for clinical and epidemiologic purposes Antimicrobial susceptibility testing is one of the most important and useful tests performed by the clinical microbiology laboratory.
What is the discs-diffusion test?
The discs-diffusion test is based on the fact that for a given antibiotic, the size of the zone inhibition is inversely related to MIC (determined by dilution method) of the strain being tested when the test conditions are held constant.
Can erythromycin disk diffusion susceptibility be used as a screening test?
Given the practicality of disk diffusion and the availability of disks and controls, it has been suggested that at least erythromycin disk diffusion susceptibility could be used as a screening test . This would be feasible given the potential to use isolation agar that is devoid of selective supplement.
How does the antibiotic concentration gradient method work?
This method works because the antibiotic in the disc diffuses out into the agar, creating a concentration gradient. The concentration of antibiotic near the disc is high and gradually decreases the farther from the disc it diffuses.