Novobiocin is produced by the bacteria streptomyces

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Novobiocin is produced by the bacteria,Streptomyces.
Figure 3.DNA replication.Explore GentamicinGentamicinis a narrow spectrum, bacteriostatic antibiotic that targetsaerobic, Gram-negative bacteria and Gram-positiveStaphylococcus.Gentamicin binds with bacterial ribosomes, cellular structuresresponsible for protein synthesis. See Figure 4. When ribosomes arebound with gentamicin they are no longer able to synthesize proteinand the bacterial cell ceases to grow and divide. Gentamicin issynthesized by the Gram-positive bacteria,Micromonospora.
Figure 4.Protein synthesis.Explore Kirby-Bauer Diffusion TestThe most common method used in hospital laboratories to assessbacterial antibiotic resistance is theKirby-Bauer Diffusion test. TheKirby-Bauer Diffusion test is performed using commercially preparedfilter paper disks that have been infused with a specified concentrationof a particular antibiotic. When placed on an agar containing newlyplated bacteria, the antibiotic diffuses away from the disk into theagar, creating a concentration gradient that decreases logarithmicallywith the distance from the disk. As the bacteria grow, they will beinhibited in regions where the antibiotic concentration is above whatthe microorganism can handle. Areas where the antibioticconcentration is low will allow for bacterial growth; this growth will leadto the creation of a lawn across the plate, creating a zone around eachdisk. See Figure 5.Figure 5.Kirby-Bauer Diffusion test plate with zones of inhibition.The diameter of thiszone of inhibitionis measured in millimetersand compared to a chart that links the size of the zone of inhibition tothe dosage that is often administered to a patient. The diameter of thezone is dependent on the sensitivity of a microorganism to a particularantibiotic and the physical properties of the antibiotic itself. Someantibiotics are not as soluble as others and as such will have a differentdiffusion rate through the agar. Therefore, a very large zone ofinhibition does not necessarily mean that the antibiotic is extremelyeffective. The effective size for a zone of inhibition is calculatedthrough hundreds of assays on many different strains of bacterialisolates correlating this information with many other susceptibilitytests. In this method, an organism may be categorized as resistant,susceptible, or intermediate to a panel of antimicrobial agents. Anintermediate result is based on when the results can be influenced byother factors. For example, the zone of inhibition may indicate thepossibility that an agent would be effective, but the site of infection
and the ability of the antibiotic to reach this site is suspect, and maynot fully reach inhibitory concentrations. Under this circumstance, itwould be recommended that a different antibiotic be selected.

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Term
Summer
Professor
MargaretaFarrell

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