抗生素英文课件精品kirbybauer

Kirby-Bauer Test,Testing for Antibiotic Resistance,Why bother testing?,K-B Test is routinely done to monitor the prevalence of antibiotic resistant bacteria Observe for a trend in order to take precautionary measures For example: development of new drugs determining the molecular basis for resistance and modify existing drugs accordingly,Procedures,Prepare a pure culture (18-24 hrs) of the sample on a non-selective medium Adjust turbidity until it is equivalent to the 0.5 McFarland Turbidity Standard,0.5 McFarland Standard,Sample,Within 15 minutes of adjusting the turbidity dip a sterile cotton swab into the sample streak a lawn of bacteria on Mueller-Hinton agar,Leave the lid agar for 3-5 minutes (no more than 15 minutes) to allow plate to dry,Procedures,Procedures,Apply antibiotic impregnated disks on the bacterial lawn Important: where the disk drops is where it stays Incubate for 16-18 hours at 33 2oC unless otherwise instructed,Note: 1) For testing Staphylococci with oxacillin use M-H agar supplemented with 2% NaCl incubate for 24 hours at 33 2oC For testing Staphylococci with vancomycin use unsupplemented M-H agar incubate for 24 hours at 33 2oC,Results,Antibiotics diffuse out onto the agar Concentration of antibiotics decrease as they diffuse further away from the disks After incubation, observe for a clearing on the bacterial lawn (zone of inhibition),Bacterial growth,Zone of inhibition,Results,Measure the diameters of the zone of inhibition Interpret the results as “resistant” or “susceptible” according to the guideline provided by the NCCLS Interpretation of the zone of inhibition is different for each bacteria-antibiotic combination,E-test,Same principle as the Kirby-Bauer Test Uses a plastic strip with a predefined gradient of antibiotic concentration Results are read directly on the strip where the zone of inhibition intersects with the strip,Results,Interpret results as “resistant” or “susceptible” according to the guidelines provided in the package insert For ambiguous results, refer to the provided reading guide for : Organism related effects Drug related effects Resistance mechanism related effects Technical and handling effects,API Staph Test,Identification of the genera Staphylococcus Micrococcus Kocuria 20 microtubules with dehydrated substrates plus one lysostaphin resistance test,Procedures,Prepare the incubation box Prepare pure culture (18-24 hrs) on P agar or Columbia blood agar Make a homogeneous bacterial suspension using the API Staph Medium Adjust turbidity equivalent to 0.5 McFarland,P agar,API Staph Medium,0.5 McFarland Standard,Procedures,Inoculate the microtubes Top off the inoculum with mineral oil if instructed Incubate for 18-24 hours at 36 2oC Develop the reactions as necessary,Procedures,Lysostaphin Resistance Test,Flood P agar with bacterial suspension w/ 107 cells/ml,Let dry for 10-20 minutes at 36 2oC,Incubate for 18-24 hours at 35-37oC,Any degree of lysis indicates a negative result on the 21st test of the strip,Results,Record each microtube as a +/- reaction Microtubes in groups of 3 Each one is assigned a value of 1, 2 or 4 In e