page_title: Antibiotic sensitivity testing
hierarchical_section_title: Antibiotic sensitivity testing
caption_attribution_description: English: Staphylococcus aureus growing on a nutrient agar. The discs contain an antibiotic. The bacterium is completely resistant to three of the antibiotics. The zones around the discs are where the bacteria have not grown because they are sensitive to the antibiotic in each of the discs of filter paper.
context_page_description: Antibiotic sensitivity testing or antibiotic susceptibility testing is the measurement of the susceptibility of bacteria to antibiotics. It is used because bacteria may have resistance to some antibiotics. Sensitivity testing results can allow a clinician to change the choice of antibiotics from empiric therapy, which is when an antibiotic is commenced based on clinical suspicion about the site of an infection and common bacteria that cause this, to directed therapy, which is when an antibiotic is commenced based on knowledge of a causative organism and its sensitivities.
  Sensitivity testing usually occurs in a laboratory, and may be based on culture methods that expose bacteria to antibiotics, or genetic methods that test to see if bacteria have genes that confer resistance. Culture methods often involve measuring the diameter of the zones of inhibition on agar culture dishes of bacterial growth around paper discs that are impregnated with antibiotics. The lowest concentration of the antibiotic that stops the growth of bacteria is the minimum inhibitory concentration, and can be determined from this.
context_section_description: Antibiotic sensitivity testing or antibiotic susceptibility testing is the measurement of the susceptibility of bacteria to antibiotics. It is used because bacteria may have resistance to some antibiotics. Sensitivity testing results can allow a clinician to change the choice of antibiotics from empiric therapy, which is when an antibiotic is commenced based on clinical suspicion about the site of an infection and common bacteria that cause this, to directed therapy, which is when an antibiotic is commenced based on knowledge of a causative organism and its sensitivities. 
  Sensitivity testing usually occurs in a laboratory, and may be based on culture methods that expose bacteria to antibiotics, or genetic methods that test to see if bacteria have genes that confer resistance. Culture methods often involve measuring the diameter of the zones of inhibition on agar culture dishes of bacterial growth around paper discs that are impregnated with antibiotics. The lowest concentration of the antibiotic that stops the growth of bacteria is the minimum inhibitory concentration, and can be determined from this.
  Antibiotic susceptibility testing has occurred since the discovery of the beta-lactam antibiotic penicillin. Initial methods were phenotypic, and involved culture or dilution. The Etest, an antibiotic impregnated strip, was available since the 1980s, and genetic methods such as polymerase chain reaction (PCR) testing have been available since the early 2000s. Research is ongoing into improving current methods by making them faster or more accurate, as well as developing new methods for testing, such as microfluidics.
caption: Example of antibiotic sensitivity testing. Thin paper discs containing an antibiotic have been placed on an agar plate growing bacteria. Bacteria are not able to grow around antibiotics to which they are sensitive. This is called "the zone of inhibition".
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