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Unit 2 Chapter 13
Antimicrobial Susceptibilty Testing
Question | Answer |
---|---|
Define MIC | minimal inhibitory concentration - lowest concentration of antimicrobial agent that inhibits the growth of a bacterium |
Define McFarland Turbidity standards | used to quantify suspensions of latex particles or barium sulfate prepared at various densities to represent specific numbers of bacteria. |
Explain Broth Macrodilution | broth dilution MIC tests performed in test tubes are referred to as broth macrodilution MIC or tube dilution MIC tests. Generally, a twofold serial dilution series, each containing 1 to 2 mL of antimicrobial solutions |
Kirby Bauer test *principle* | thoroughly tested for its composition and its pH level; ensures that zones of inhibitions can be reproduced from the same organism; does not inhibit sulfonamides; ensures standardization and reproducibility. |
Kirby Bauer test *reagents* | Mueller Hinton agar plates; BBL BD Sensi Disks (various antimicrobials as in QC above); 37 C Incubator; Sterile polyester or cotton swabs; BBL Prompt inoculation system; Calipers, ruler, or template for measuring the diameters of inhibitory zones. |
Kirby Bauer test *result reporting* | determine the susceptibility/resistance of organism to each drug tested there are different charts for different organisms; for each drug indicate whether the zone size is susceptible (S), intermediate (I), or resistant (R) ; zone sizes are not reported |
Kirby Bauer test *additional* | culture medium is inoculated with test organism; filter paper discs, are placed on the medium. The organism will grow; the antibiotic inhibits the growth. If the organism is susceptible to a specific antibiotic, there will be no growth around the disc |
Etest *principle* | quantitative method that applies both the dilution of antibiotic and diffusion of antibiotic into the medium;consists of a predefined, continuous, exponential gradient of antibiotic concentrations immobilized along a rectangular plastic test strip. |
Etest *reagents* | Etest is supplied in a package of 100 or 30 (some reagents) test strips of one antimicrobial agent |
Etest *result reporting* | Read at point where ellipse intersects the scale. If a value between two twofold dilutions is seen, always round up; read value at complete inhibition of all growth; If the intersect differs on either side of the strip, read as the greater value. |
Etest *additional* | quantitative technique for determining antimicrobial susceptibility of Gram -/+ aerobic bacteria (En- terobacteriaceae, Pseudomonas, Staphylococcus and, Enterococcus;, N. gonorrhoeae, S. pneumoniae , Streptococcus and Haemophilus species) |
beta-lactamase tests *principle* | enzymes that chemically inactivate β-lactam molecules by disrupting the β-lactam ring component of the molecule |
beta-lactamase tests *reagents* | filter paper disks impregnanted with nitrocefin |
beta-lactamase tests *result reporting* | Nitrocefin is a cephalosproin, susceptible to most β-lactamases, that turns pink when hydroyzed. |
beta-lactamase tests *additional* | by competing for sites on transpeptidase β-lactam antibiotics prevent essential cross linking of the peptidoglycan |
Define MBC | minimal bactericidal concentration - lowest concentration of antimicrobial agent that kills 99.9% of the test bacteria |
Define synergism | occurs when the antimicrobial activity of a combination of antimicrobial agents is greater than the activity of the individual agents alone |
Define antagonism | occurs when the antimicrobial activity of combination of antimicrobial agents is less than the activity of the individual agent alone |
Define indifference | occurs when the antimicrobial activity of a combination of antimicrobial agents is equal to the activity of the individual agents. |