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Name: Jon
Status: Other
Grade:  Other
Location: GA
Country: United States
Date: July 2008

For a given antibiotic is there a difference in susceptibility between the gram+ and the Gram- bacteria?

The difference between Gram+ and Gram- is in the cell walls of the bacteria, so for example Penicillin, which inhibits the synthesis of Gram- cell walls, does not work against Gram+ bacteria.

Ron Baker, Ph.D.

It depends on the antibiotic but yes. Even if two bacteria are susceptible to the same antibiotic, they may not be AS sensitive. Many antibiotics work by breaking down components in the cell wall called peptidoglycans (PG). They act like a chain link fence to hold the cell wall together. It's like taking a wire cutter and clipping the fence. Gram positives have a much thicker layer of PG than gram negatives even though both have them. So is you are talking about one of these there is probably a difference. Other antibiotics work by other means and it may not make a difference if they are g+ or g-.


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