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Antimicrobial susceptibility testing advances along with antimicrobial resistance threats
Michelle Powell 859

Antimicrobial susceptibility testing advances along with antimicrobial resistance threats

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Antimicrobial Resistance

Loren Bonner

A recent paper, published February 24, 2023, in Pharmacotherapy, lays out the most up-to-date diagnostic stewardship—including education, communication, and interpretation—as it relates to antimicrobial susceptibility testing.

In the 14 years since the last antimicrobial susceptibility testing update was published, there has been a surge of approvals of rapid diagnostic platforms. Of course, antimicrobial resistance has only worsened during this period of time, as well.

According to lead author Elizabeth Hirsch, PharmD, the review is meant to provide clinicians with a summary of both conventional susceptibility testing methods and newer rapid methods, along with guidance on their implementation and optimization.

Hirsch and colleagues write that “antimicrobial susceptibility testing has been the cornerstone of optimal antimicrobial therapy for more than a century and will continue to play a critical role in ensuring adequate therapy for patients, as well as tracking and monitoring the spread of AMR [antimicrobial resistance].”

Defining antimicrobial susceptibility testing

According to NIH’s National Library of Medicine, antimicrobial susceptibility testing (AST) is “a laboratory procedure performed by medical technologists (clinical laboratory scientists) to identify which antimicrobial regimen is specifically effective for individual patients. On a larger scale, it aids in the evaluation of treatment services provided by hospitals, clinics, and national programs for the control and prevention of infectious diseases.”

The National Library of Medicine’s definition also states that researchers have had to recently put continuous surveillance activities into practice for resistance patterns due to mutations in bacterial DNA.

Laboratories have many methods to chose from, including broth microdilution, agar dilution, and disk diffusion. Technological advances such as the development of commercial automated susceptibility testing platforms and the advent of rapid diagnostic tests (RDTs) have improved the rapidity, robustness, and clinical application of AST, according to authors of the review paper.

“Although many of the AST methods developed at the turn of the twentieth century are still in routine use today, the past decade has seen an explosion in new technologies including molecular and phenotypic RDTs, and more frequent updates and revisions to clinical breakpoints,” the review authors write. “These rapid advances in the antimicrobial use process make strong collaborations between clinicians and microbiologists essential. Moving closer to the goal of immediate antimicrobial therapy optimization with little to no delay would benefit patients afflicted with an infectious disease syndrome.”

Application to pharmacists

“The increase in new technologies, including molecular and phenotypic rapid diagnostic tests, and more frequent updates and revisions to clinical breakpoints highlight the essential need for strong collaborations between pharmacist clinicians and microbiologists,” said Hirsch, who is an associate professor in the Department of Experimental and Clinical Pharmacology at the University of Minnesota College of Pharmacy.

The only way to effectively battle antimicrobial resistance while improving patient outcomes and appropriate antimicrobial use is to take a comprehensive approach, she said.

“Pharmacists are uniquely positioned to serve as these liaisons—and often serve in integral roles—among many antimicrobial stewardship programs,” said Hirsch.

While the review paper is useful for infectious disease pharmacists or those working in antimicrobial stewardship, Hirsch said it’s also written for noninfectious disease experts.

“[It’s] especially useful for trainees and students wanting to learn more about susceptibility testing methods and diagnostic stewardship,” said Hirsch. “It is highly encouraged as reading prior to any inpatient/outpatient APPE or rotation experience where a learner may need to interpret culture results and susceptibility testing in order to make recommendations surrounding antibiotic treatment or monitoring.” ■

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