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, if a narrow spectrum drug is used on an incorrectly identified microbe, then there will be no antibacterial coverage and the harmful bacteria may flourish. Unfortunately, the use of antibiotics in antimicrobial control has consequences. Microbes have been adapting to overcome harmful environments since the beginning of life. Exposure of microbes to antibiotics is yet another environment and as a result, antimicrobial resistance has surfaced.
Some common resistant mechanisms include the production of inactivating enzymes that leave the antimicrobial ineffective. Interruption of cell membrane transport of antimicrobial agents is another development of resistance. Mutations are a common mechanism of antimicrobial resistance. Penicillin can be rendered ineffective by an alteration mutation that disrupts the target protein. The Kirby-Bauer test is an agar diffusion test used to identify bacterial susceptibilities. When S. epidermidis is exposed to antibiotic disc materials of Novobiocin, Penicillin and Gentamicin, the most resistance observed was by the Penicillin.