Question: Evaluation Of Antibiotics Kirby Bauer Method (1) – Saved To My Mac References Mailings Review View Tell Me Aa AO DE Abecede Acce AaBbCD Aalbcdi AaBb Na Song Heating Heading 2 Dates, Fixes, And Improvements, Choose Check For Updates Antibiotic Sensitivity Testing- Kirby Bauer Method Virtual Lab Introduction And Background Antimicrobials Are Compounds …
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Evaluation of Antibiotics Kirby Bauer Method (1) – Saved to my Mac References Mailings Review View Tell me Aa AO DE Abecede Acce AaBbCD Aalbcdi AaBb Na Song Heating Heading 2 dates, fixes, and improvements, choose Check for Updates Antibiotic Sensitivity Testing- Kirby Bauer Method Virtual Lab Introduction and background Antimicrobials are compounds that kill or inhibit growth of microorganisms. Antibiotics are antimicrobials produced by microorganisms that inhibit or kill other microbes. Many times these antibiotics are chemically altered and referred to as semi-synthetics. Synthetic antimicrobials are manufactured in the lab. The Kirby-Bauer test for antibiotic susceptibility, called the disc diffusion test, is a standard test for measuring the effectiveness of antimicrobials against pathogenic microorganisms that has been used for years. The special culture medium used for the antibiotic susceptibility test is Mueller-Hinton Agar. The MH Agar has a pH between 7.2 and 7.4 and must be poured to a depth of 4mm in either 150mm or 100mm Petri dishes. The depth is important in order to ensure proper diffusion of the antimicrobial agent from the disc. A very thick agar will slow down the lateral diffusion of the antimicrobial agent and thus produce smaller zones of inhibition. The inoculation is also done using a broth culture that is diluted to match a specific turbidity standard (0.5 McFarland turbidity standard). Procedure: The bacterium is thoroughly swabbed using a sterile cotton swab on the agar and the antibiotic discs are placed on top. The antibiotic diffuses from the disc into the agar in decreasing amounts the further it is away from the disc. If the organism is killed or inhibited by the concentration of the antibiotic, there will be NO growth in the immediate area around the disc: This is called the zone of inhibition. The size of the zone of inhibition depends upon the sensitivity of the bacteria to the specific antimicrobial agent and the point at which the antimicrobial agent’s minimum inhibitory concentration (MIC) is reached. The zone sizes are looked up on a standardized chart to give a result of sensitive, resistant, or intermediate. and improvements, choose Check for Updates. the concentration or the dTICIDIOCIC, there wil e grow Termeuldte dred around in disc: This is called the zone of inhibition. The size of the zone of inhibition depends upon the sensitivity of the bacteria to the specific antimicrobial agent and the point at which the antimicrobial agent’s minimum inhibitory concentration (MIC) is reached. The zone sizes are looked up on a standardized chart to give a result of sensitive, resistant, or intermediate. Answer these questions (8 questions – 8 points) – 1) The best medium to use for antibiotic susceptibility testing is reason why this medium is preferred is the 2) Area of no growth around antibiotic disk is called the and it indicates that the 3) Factors which influence antibiotic susceptibility testing are 4) How does the antibiotic get from the disk into the agar? 5) What factors influence the size of the zone of inhibition for the antibiotic? 6) Why are certain gram-negative bacteria more resistant than gram positive bacteria to antibiotics that attack cytoplasmic targets? 7) Why are certain gram-positive bacteria more resistant to antibiotics that attack the plasma membrane such as polymyxin? plasma membrane such as polymyxin? 8) The following is the data obtained for the Antibiotic Sensitivity Test done on three bacterial samples. Using the Zone Diameter Interpretation Chart given below, for each bacterium, indicate whether it is Resistant (R), Intermediate (1), or Sensitive (S) to each of the antibiotics in the results table provided. Data Obtained from the Antibiotic Sensitivity Test Lab Antibiotics Tested S. aureus E. coli P. aeruginosa Chloramphenicol 20 17 0 Cipro 29 30 29 SXT 23 20 0 Penicillin 10 20 0 Ampicillin 17 0 Bacitracin (10) 14 0 0 Tetracycline (30) 25 17 0 Streptomycin (10) 16 12 10 Zone Diameter Interpretation Chart Antibiotic Disk Potency 30 με 5 WE 548 10 U Chloramphenicol Cipro SXT (Sulfa) Penicillin Ampicillin Bacitracin Tetracycline Streptomycin Zone of Inhibition Diameter (mm) Resistant Intermediate Sensitive/Susceptible $ 12 13-17 2 18 5 15 16 – 20 221 5 10 11-15 216 S 28 N/A 229 59 N/A 2 10 58 9-12 2 13 S 15 16-32 2 33 5 11 12-14 2 15 10 48 10 U 30 US 10 E Results Table S. aureus E. coli P. aeruginosa Antibiotics Tested Chloramphenicol Cipro SXT Penicillin 10 Ampicillin Bacitracin (10) Tetracycline (30) Streptomycin (10)
