Why Antimicrobial Susceptibility Testing is important?

There is a long list of antimicrobial agents (AMA) available commercially but any one AMA may have variable bactericidal action against different pathogenic bacteria. Antimicrobial susceptibility testing is way of determining action of an antimicrobial agent (antibiotic) against any isolated pathogenic bacteria in a given case. The presumptive identification of a bacterial infection is made by Gram staining of samples obtained from infected sites with sterile precautions. Later the organisms (bacteria) are grown on artificial media in the laboratory and definitive identification is made for antibiotic sensitivity or antimicrobial susceptibility testing. For a legitimate report on antimicrobial susceptibility test, the physician as well as the microbiologist should keep the following points in mind:

• Specimen should be collected/obtained before initiation of any tentative antibiotic/antimicrobial therapy.


• Specimen should not be contaminated with indigenous microbial flora.


• Clinical note of the treating physician should accompany the request for antimicrobial susceptibility testing.

Antimicrobial susceptibility testing is of utmost importance as it culminates the following objectives:

• It provides guidance to the clinicians in getting definitive information in the selection of most appropriate antibiotics/AMA against the infectious agents.


• It directs the line of treatment towards the limited spectrum and least expensive antibiotics/AMA to which the isolated pathogen would respond.


• It predicts about the outcome of the treatment with the specified antibiotic/AMA. The implication of the result 'susceptible' or 'sensitive' is that there would be high probability of treatment of infection with the specified antibiotic/AMA. A 'moderately susceptible/sensitive' result indicates a need for high dose of the drug would be required for treatment and a 'resistant' result indicates that the treatment with the pointed out antibiotic/AMA would not be possible.

Antimicrobial Chemotherapy

Antimicrobial chemotherapy or antibiotic therapy assists our body in the fight against the intruding infectious organisms, mainly bacteria. Majority of bacteria are non-pathogenic and many types of these have symbiotic existence in our body. The pathogenic species of bacteria have been found sensitive to a variety of antibiotics; however, some of these have become resistant to antibiotics. Despite the advancement in diagnostic facilities and availability of a large number of antibiotics, still a patient may die due to infection of drug resistant bacteria. Suboptimal and inappropriate use of antibiotics has probably led to the development of resistance to antibiotics in bacteria. Only a well equipped Microbiology Laboratory can determine the antimicrobial susceptibility of clinically significant bacteria isolated from biological specimens like blood, urine, stool, pus, sputum or other body fluids. Advice on the most appropriate antimicrobial agent (antibiotic) must be obtained form the laboratory before starting antibiotic therapy against offending bacteria. The clinician should use reputed brands of antibiotics and report back to the drug manufacturing company and the testing laboratory for recording the trend of resistance and resistance pattern.