antimicrobial substancesused on non-living objects or outside the body.
Why antimicrobial technique is needed ?• Bacteria have the ability to develop resistance following repeated or subclinical (insufficient) doses• so more advanced antibiotics and synthetic antimicrobials are continually required to overcome them.
Technique in testing for Antibiotic sensitivity• The method includes several steps including :• obtaining a bacterial sample• identifying the type of bacteria in the bacterial sample• selecting a set of antibiotics based on the identity of the bacteria in the bacterial sample• obtaining a control sample from the bacterial sample
Antimicrobial agent placed on the surface of an agar plate It containingdisease agent shows medium that has been Disk inoculated with the how effective the disease agent beingantimicrobial agent diffusion tested, which will grow is. and fill the disk. size of the area Antimicrobial agent killing some of the diffuse into medium cleared disease agent around where the anitmicrobial agent was innoculated
For example . . . • Small wafers containing antibiotics are placed onto a plate which bacteria are growing. • If the bacteria are sensitive to the antibiotic, a clear ring, or zone of inhibition, is seen around the wafer indicating poor growthAntibiotic sensitivity testing
Zone sizes differ on sensitivity pattern• It has been determined that zones of inhibition of a certain diameter (varies for antibiotic and to a lesser extent, bacterial species) correlate with sensitivity or resistance to the antibiotic tested
Epsilometer test• to determine whether or not a specific strain of bacterium or fungus is susceptible to the action of a specific antibiotic.• commonly used in the setting of medicine, where a particular organism has been found to infect a patient, and the doctor treating the patient is seeking guidance on what concentration of antibiotic is suitable.
rectangular strip that has been impregnated with the drugEtest utilise by then A lawn of bacteria an exponential is spread and gradient of the grown on an agardrug to be tested Epsilometer plate test and producing Etest strip is laid into the agar on top Drug diffuse out
As a result . . . • an exponential scale printed on the strip . • After 24 hours of incubation, an elliptical zone of inhibition is produced • the point at which the ellipse meets the strip gives a reading for the minimun inhibitory concentration (MIC) of the drug.
Dilution plating technique• to reduce the concentration of microscopic organisms or cells in a sample• A series of cultures is tested with various concentration pf an antibiotic to determine minimum inhibiting concentration of antibiotic
spread bacteria over a wide areaThe numbers of bacteria count the number of colonies that grow on colonies that grow each plate are counted bacterial cell in the original sample should produce a single colony
Stokes’ Method• In original Stokes’ method the inoculum of the control strain is evenly spread over the upper and lower thirds of a plate• the test strain over the central third,uninoculated (gaps 2 – 3 mm wide are left to test from the control areas.
For example . .• In the Stokes controlled sensitivity test, a control organism is inoculated on part of a plate• the test organism is plated on the remainder.• Disks are placed at the interface and the zones of inhibition are compared.• The use of a sensitive control shows that the antibiotic is active• if the test organism grows up to the disk it may safely be assumed that the test organism is resistant to that drug.
Testing Minimum Inhibitory Concentration• In alternative measure of susceptibility is to determine the Minimum Inhibitory Concentration (MIC) and the Minimum Bactericidal Concentration (MBC) of a drug.• Both are mixed with serially diluted antibiotic solutions and a standard inoculum is applied.• After incubation, the MIC is the first broth in which growth of the organism has been
What is MinimumInhibitory concentration• Minimum inhibitory concentration (MIC), in is the lowest concentration of an antimicrobial that will inhibit the visible growth of a micro organism after overnight incubation.• Minimum inhibitory concentrations are important in diagnostic laboratories to confirm resistance of micro organisms to an antimicrobial agent and also to monitor the activity of new antimicrobial agents.
The Antibiotics are diluted to various dilutionto test the minimum inhibitory concentration