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The Explanation of Antibiotics, Antibacterials, Agar Well Difussion Method & Total Plate Count (TPC)

Antibiotics

Antibiotics are microorganisms that can inhibit harmful microorganisms in the body, such as in infections. According to Hakam (2016), based on antibiotic activity, antibiotics are divided into 2 groups: broad-spectrum antibiotics and narrow-spectrum antibiotics.  

1. Broad-spectrum antibiotics  

This type of antibiotic can kill both Gram-positive and Gram-negative bacteria. This antibiotic can broadly kill bacteria, viruses, and protozoa. Examples include chloramphenicol, tetracycline, and ampicillin.  

2. Narrow-spectrum antibiotics  

This type of antibiotic is only active against several types of bacteria. Examples include neomycin, penicillin, and streptomycin.

Antibacterials

Antibacterials are substances that can inhibit bacterial growth and can kill pathogenic bacteria by disrupting metabolism or damaging the cell wall of pathogenic bacteria. Antibacterials are distinguished into 2 types: bacteriostatic and bactericidal, which can kill bacteria. Antibacterials are used to kill bacteria that have selective toxicity and to determine the sensitivity threshold of an antibacterial compound against certain bacteria.

Agar Well Diffusion

Agar Well Diffusion is one of the in vitro antimicrobial activity test methods that is relatively the cheapest and easiest. Antibacterial testing using this method is carried out by inoculating an agar plate with pathogenic bacterial species using the spread plate technique. This process is done by spreading a microbial solution with a certain volume onto the surface of the agar medium using an L-glass spreader. The next step is to make holes or wells (diameter 6 to 8 mm) aseptically using a sterile cork borer or an ose needle loop. The well or hole is then filled with liquid bacterial culture according to a certain volume, and then the antibacterial culture results on the agar plate are incubated at the appropriate temperature and conditions. During incubation, the liquid bacterial culture solution as an antibacterial gradually diffuses through the agar medium and inhibits the growth of the tested pathogenic bacterial species. This process produces an inhibition zone, so the inhibition zone can be observed, and the diameter of the zone is measured using calipers.

Total Plate Count (TPC)

Total Plate Count (TPC) is a method of growing live microbial cells on agar media, so that microorganisms will multiply and form colonies that can be seen directly and counted with the naked eye without using a microscope. Total Plate Count (TPC) testing is intended to show the number of microbes present in a product by counting bacterial colonies grown on agar media. The specific requirement for counting the number of bacterial colonies according to the standard (Standard Plate Count) is that there must be 30-300 bacterial colonies. The calculation of the number of bacterial colonies that grow, based on the TPC test results conducted, is only performed on dilutions with colony counts between 30-300. This is done to reduce the possibility of errors in calculation, and the method for calculating is: all colonies per mL or per gram = number of colonies on the plate × dilution factor.

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