Effects of Antimicrobials

The Student Vet

Oct 2, 20184 min read

Updated: Dec 18, 2018

For one of my required practicals I had to research into the effects of antimicrobials using aseptic techniques. However, once I started researching I found it interesting and decided to look deeper into antiseptic techniques and practical uses of them.

Use of multi-discs:

Antibiotic multi-discs are used in Agar Diffusion Tests. This test is a method of establishing the sensitivity of bacteria. It uses antibiotic multi-discs to test the extent to which the selected bacteria are affected by the antibiotics. The multi-disc is an efficient and cost effective way of testing the bacteria against 8 different antibiotics. Each antibiotic acts as an individual test but they can all be don at the same time. The multi-discs are placed onto the surface of a petri dish which contains a culture medium inoculated with colonies of microorganisms from a broth. The plate is then incubated with the multi-disc on and afterwards is examined to reveal the effect of the different antibiotics. The inhibition rings around the discs are compared to standard in inhibition rings and this allows us to classify the microorganism as susceptible, intermediate of resistant to the tested antibiotic. In incubation the plates will never be stored at a temperature similar to that of the human body as that will promote growth of microbes that can survive in that optimum temperature which increases the risk of transmission to people and the spread of the microorganisms.

Bacillus Megaterium:

This microorganism is an aerobic spore forming bacterium. It is amongst the biggest known bacteria and is often joined in pairs or chains. It is because of this immense size that B. megaterium is used to study structure, protein localisation and membranes of bacteria. The bacteria are also gram positive rods which allows us to visually see the cell wall as the bacteria is able to be stained purple using the Gram Stain technique. This staining technique reveals that the bacteria have a thick cell wall made of peptidoglycan.

The bacteria are used is a wide range of medical and industrial areas such as acting as an agent in biocontrol of plant diseases. B. megaterium is effective at this as it produces penicillin amidase which is used to make synthetic penicillin. The bacteria are also used as in indicator in glucose dehydrogenase, which is used in glucose blood testing, and amylases used in the baking industry.

Multi Disc Antibiotics:

Chloramphenicol- is an antibiotic used to treat a number of bacterial infections. It is mainly used to treat eye infections such as conjunctivitis. It works by interfering with protein synthesis. This bacteriostatic prevents protein chain elongation by inhibiting the peptidyl transferase activity of the ribosome. It binds to specific residues in the 23S rRNA subunit which prevents a peptide bonds from forming.

Erythromycin- is an antibiotic used widely to treat chest infections, skin problems and STIs. It is known as a macrolide antibiotic and works by preventing bacteria from producing essential proteins. The lack of these vital proteins restricts the bacteria’s growth and its ability to replicate.

Fusidic Acid- is a steroid antibiotic mainly used in creams and eye drops. It can be used to treat bacterial skin and eye infections. The ointment contains sodium fusidate which is the sodium salt of Fusidic acid. It prevents bacteria from producing essential proteins. It leaves the bacteria unable to increase in numbers allowing the immune system to destroy them.

Oxacillin- is an antibiotic in the penicillin group of antibiotics. It is used to treat different bacterial infections such as Staphylococcal infections. It kills bacteria by binding to enzymes involves in the synthesis of the bacterial cell wall. This decreases the effectivity of the cell wall and causes the bacteria to die.

Novobiocin-is an antibiotic compound which is known as an aminocoumarin antibiotic. Novobiocin inhibits the bacteria’s DNA synthesis process by targeting DNA gyrase and its enzyme DNA topoisomerase IV. DNA gyrase is an essential enzyme for DNA replication as it catalyses the supercoiling of double stranded closed circular DNA. By binding to DNA gyrase the Novobiocin blocks ATP activity preventing the DNA from supercoiling.

Penicillin G- also known as benzylpenicillin, is a penicillin derivative most commonly used in the form of its sodium or potassium salts when used to treat an array of bacterial infections. It is effective against most gram-positive bacteria. Penicillin G is a natural penicillin and is administered intravenously or intramuscularly as it is poorly absorbed orally. Penicillin kills bacteria by inhibiting the transpeptidase which catalyses the final step in cell wall biosynthesis.

Strephtomycin- is an antibiotic used to treat infections such as TB and endocarditis. It acts by binding to the ribosomal subunit and disrupting the initiation and elongation steps on protein synthesis.

Tetracyline- is a broad spectrum antibiotic used to treat a wide array of bacterial infections like acne. It works by stopping the growth of bacteria. It does this by binding to a ribosomal subunit and preventing the incoming tRNA from attaching to the ribosomal acceptor site. It also can alter the cytoplasmic membrane and cause intracellular components to leak out.