Which antibiotic drug is the most effective against staph aureus, E. coli, Prote

Question

Which antibiotic drug is the most effective against staph aureus, E. coli, Proteus Vulgaris, or Pseudomonas aeruginosa? What's the purpose of this lab and the observation and conclusion? LAB 17: ANTIMICROBIC SENSITIVITY TESTING A. Introduction i. Antimicrobic drugs, including antibiotics, sulfonamides, and chemotherapeutics, are effective treatments against bacterial infections 2. Antimicrobic sensitivity testing allows physicians and pathologists to use the most effective drug for a specific disease 3. The Kirby-Bauer method of testing antimicrobic sensitivity is used by the FDA as a standard procedure 4. A special culture medium called Mueller-Hinton agar is recommended for the Kirby-Bauer method B. Procedure 1. This lab is done in a group at each table 2. Each group should obtain 4 Mueller-Hinton agar plates 3. Follow aseptic procedure, inoculate each plate using a sterile cotton swab with one of the 4 cultures Staph aureus, E coli, Proteus vulgaris, and Pseudomonas aeruginosa (be sure the entire surface of the agar plate is inoculated) 4. Carefully dispense antibiotic disks onto each plate (use a cotton swap to lightly press each disk onto the agar surface): IStandard codes used for antibiotic disksj B bacitracin E erythromycin AM ampicillin N neomycin P penicillin S streptomycin TE tetramycin VA vancomycin 5. Write the name of culture and your name onto each plate 6. Place the plates into the designated racks inverted for incubation 7. In the next lab period, recover your 4 plates 8. Using a ruler, measure the zone of inhibition next to each antibiotic disk (use mm as unit) 9 Which antibiotic drug is the most effective against Staph aureus, E coli, Proteus vulgaris, or Pseudomonas aeruginosa?

Explanation / Answer

Mueller Hinton agar is the best routinely used standard agar for antimicrobial susceptibility tests for both aerobic and facultative anaerobes. It is widely used for its properties of being non-selective and non-differential, good batch to batch reproducibility, presence of starch as a constituent (which traps toxins produced by bacteria) and has excellent diffusion properties.

Each antibiotic has a specific mode of action which it employs to destroy microorganisms.

Ampicillin – modified (semi synthetic) form of penicillin. It shows high activity against both gram positive and geam negative bacteria.

Neomycin – inhibits protein synthesis by binding to 30S ribosome subunit.

Tetramycin – It is also known as tetracycline. These inhibit protein synthesis by preventing thje binding of aminoacyl-tRNA to mRNA –ribosome complex.

Bacitracin – Cell wall synthesis inhibitor

Penicillin – It prevents complete synthesis of peptidoglycan (important cell wall component). Penicillin is a B-lactum antibiotic. It binds irreversibly to transpeptidase and inhibits cell wall biosynthesis.

Vancomycin – it inhibits cell wall biosynthesis by binding to transporter protein – (Ala-Ala dipeptide).

Erythromycin – inhibits protein synthesis by binding to free ribosomes

Streptomycin – inhibits protein synthesis by binding to 30S ribosome subunit.

Observation –

The susceptibility of drug is determined from the diameter of zone of inhibition ( quantified using a vernier calipers or thin millimeter scale and measured upto the nearest mm).

based on the zone size, a conclusion can be made and the organism can be entitled as sensitive, intermediate or resistant to the tested antibiotic.

Since this is an experimental procedure to be carried out in the lab, the results can only be identified based on your lab work.

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