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Appropriate antibiotics usually eliminate bacteria. However are the same antibiotics as effective against bacteria that have grown to form a colony?

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  • $\begingroup$ I'm not entirely sure what you're asking, but some bacteria can form structures called biofilms, which often allow them to resist concentrations of antibiotics that are normally fatal to individual bacteria. $\endgroup$ – user137 Jun 29 '16 at 2:55
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    $\begingroup$ Usually, if there is a need to take antibiotics, it means there are multiple colonies of bacteria already in the body and as such the express purpose of taking antibiotics is to destroy those colonies. $\endgroup$ – One Face Jun 29 '16 at 3:24
  • $\begingroup$ I have rewritten the title and question, based on the accepted answer. I am not a bacteriologist so, if necessary, perhaps @WYSIWYG might need to make further modifications. $\endgroup$ – David Jun 29 '16 at 9:14
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It depends on the kind of antibiotic. Some antibiotic are bacteriostatic i.e. they primarily stop the growth while some are bactericidal i.e. they kill the living bacterial cells. Some antibiotics can have mixed effects. Bacteriostatic antibiotics would not be very efficient in eliminating a colony.

Apart from the mechanism of action, there can be other factors that would dictate the efficacy of the antibiotic; these can all be considered under pharmacokinetics/pharmacodynamics:

  • Degradation/clearance rate of antibiotic
  • Rate of diffusion of antibiotic inside the bacterial colony (this rate would be less when the cells are inside a big colony compared to when they are disperse).
  • Community organization and dynamics inside the colony (like user137 said in their comment, certain biofilms can be more resistant to antibiotics)
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  • $\begingroup$ can bacteriostatic antibiotics kill individual organisms? $\endgroup$ – One Face Jun 29 '16 at 13:34
  • $\begingroup$ @OneFace Eventually because the organisms won't be able to grow, but not directly. $\endgroup$ – WYSIWYG Jun 30 '16 at 8:58

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