The invention provides methods for the rapid determination of the antibiotic susceptibility of a microorganism, such as, an infectious microorganism in a biological sample, using fluorescence in situ hybridization ("FISH"). Methods of the invention may be applied to the rapid identification, typing, antibiotic susceptibility determination, and/or antibiotic minimum inhibitory concentration (MIC) determination for any infectious microorganism, such as a Gram positive bacteria, a Gram negative bacteria, or a yeast.
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