infections
Diagnosis of Infectious Disease
Testing a Microorganism's Susceptibility and Sensitivity to Antimicrobial Drugs
Although doctors know in general which antimicrobial drugs are effective against different microorganisms, microorganisms are constantly developing Antibiotic Resistance that were previously effective. Thus, susceptibility testing is done to determine how effective various antimicrobial drugs are against the specific microorganism infecting the person. This testing helps doctors determine which drug to use for a particular person's infection (see Cultures are often used for susceptibility testing. Once a microorganism has been grown in a culture, doctors add different antimicrobial drugs to see which ones kill the microorganism. They also test how sensitive the microorganism is to a drug—that is, whether a small or a large amount of a drug is needed to kill the microorganism (sensitivity testing). If a large amount is needed to kill the microorganism in the laboratory, doctors usually do not use that drug. Sometimes Tests That Detect Genetic Material in Microorganisms can be used to detect genes in the microorganism that cause resistance to certain antimicrobial drugs. For example, methicillin-resistant Because susceptibility testing occurs in the laboratory, the result does not always match what happens in the person's body when a drug is given. Factors related to the person receiving the drug can influence how effective a drug is (see also Overview of Response to Drugs ). They include the following: How well the person's immune system is working How old the person is Whether the person has other disorders How the person's body absorbs and processes the drug 