Antibiotic Sensitivity

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Microbiology Lab
Lab 10: Antibiotic Sensitivity

April 5, 2013

Microbial growth is a normal essential part of the healthy human, animal, and plant environment. When introduction to a microorganism causes harmful bacterial growth, using antimicrobial therapy can eradicate or reduce the unwanted pathogen. Antimicrobials are used to stop the growth of a pathogen by the use of a selectively toxic, identified inhibitor. Not all microbes are harmful so it is important to uncover the the vulnerable mechanism of growth in harmful microbes and produce a toxin that is lethal to its lifecycle and not toxic to the other microbial environment nor tissue.  Some selective targets include bacterial wall composition, ribosomal synthesis, and DNA transcription.

Antibiotics are used to either inhibit or kill harmful bacterial growth. Selecting which antibiotic to use is aided by identifying which harmful bacteria are gram-positive or gram-negative. When the target bacteria is not known, a broad spectrum antibiotic may be given as it can attack both gram-positive and gram negative bacteria. A narrow spectrum antibiotic is chosen when the bacterial pathogen has been identified by gram-stain testing or symptomatic expression. A narrow-spectrum antibiotic will be used to kill the specific identified gram-negative or gram-positive bacteria.

The advantage to using a broad spectrum antibiotic is that it may be given early on, before the lengthy lab examination process so that attempts to control of growth may begin promptly. If the broad spectrum is given to a gram specific organism however, the strength of antibiotic may be insufficient to kill or control harmful growth. Furthermore, exposing a microbial environment to unnecessary types or strengths of antibiotics can lead to tolerance or super-infections.

A narrow spectrum antibiotic is an absolute advantage when the gram stain specificity is known as it will then target only the offending bacteria. Alternatively,...
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