Antimicrobial Susceptibility Testing: A Primer for Clinicians

Abstract

Appropriate use of antimicrobials in health care continues to be a challenge. Reliable and reproducible antimicrobial susceptibility testing methods are necessary to provide the clinician with valuable information that can be translated into positive clinical outcomes at the bedside. However, there are nuances with these testing methods that, if unrecognized, could lead to misinterpretation of results and inappropriate antibiotic selection. This primer describes the common antimicrobial susceptibility tests used in the clinical microbiology laboratory and reviews how subtle differences in testing methods and technique can influence reported results. Clinicians who have a thorough understanding of qualitative and quantitative methods, automated susceptibility testing systems, and commonly used screening and confirmatory tests for antibiotic-resistant organisms can strengthen institutional antibiotic stewardship programs and improve patient outcomes.

Trends in antibiotic resistance in bacterial keratitis isolates from South India

“…Anaerobic cultures were not routinely performed. Bacterial isolates from corneal scrapings were tested for susceptibility to a panel of antibiotics with a disc diffusion assay (Himedia, India), according to the manufacturer's recommendations, using resistance breakpoints according to guidelines from the Clinical and Laboratory Standards Institute (CLSI) or from the European Committee on Antimicrobial Susceptibility Testing (EUCAST) if CLSI guidelines were not available 6. CLSI and EUCAST recommend an minimum inhibitory concentration assay for vancomycin resistance in Staphylococci , but this was not performed due to limited resources.…”

Rapid phenotypic antimicrobial susceptibility testing using nanoliter arrays

“…Sample processing alone requires 24-48 h of incubation, and in the case of bacteremia and sepsis a blood culture incubation step is needed, which has a standard culture time of up to 5 d (11,12). AST testing itself then takes an additional 8-24 h. During this time, to prevent the worsening of the condition of the patient, the clinician will often prescribe an antibiotic with a broad spectrum of activity in large doses to ensure its efficacy on the target pathogen.…”

Antimicrobial susceptibility testing for bovine respiratory disease: Getting more from diagnostic results

“…Furthermore, broth microdilution testing generates a MIC value and can be formatted for automated reading. Disc diffusion testing offers the laboratory great flexibility in which antimicrobial agents are tested and is the most cost effective AST method available (Kuper et al, 2009). Broth microdilution and disc diffusion testing are labour intensive manual, require trained laboratory staff and are not applicable to all organisms, particularly slow growing and fastidious bacteria.…”