Antimicrobial Resistance Team Studies Expand Laboratory Standards

By Betty Wong

Recent studies done by CDC’s Antimicrobial Resistance Team, led by Jean Patel and including Kitty Anderson, Brandon Kitchel, David Lonsway, Linda McDougal, Kamile Rashed, Jana Swenson, Linda Weigel, and Betty Wong, have had an impact on the development of Clinical and Laboratory Standards Institute (CLSI) documents, especially those related to antimicrobial susceptibility testing methods. CLSI recently commissioned the team to validate two phenotypic tests that would detect the presence of high-level mupirocin resistance in Staphylococcus aureus and carbapenemases in Enterobacteriaceae. A carbapenemase is an enzyme that produces resistance to the carbapenems, a class of broad-spectrum antimicrobial agents reserved for treating infections caused by gram negative bacilli resistant to most other agents.

The Clinical and Laboratory Standards Institute is an international consensus body that promotes the development and use of standardized laboratory practices. As an accredited and voluntary consensus standards organization, its stated mission is to develop best practices and promote their implementation worldwide to improve patient care and medical testing practices. These practices are developed using a consensus-driven process involving industry, government, and academia and are published for use throughout the world. Standards organizations, while not actually involved in writing regulations, nevertheless play a role in shaping regulations that are adopted by regulatory bodies, such as the Food and Drug Administration and Centers for Medicare and Medicaid Services (CMS), and accrediting organizations such as The Joint Commission.

The Antimicrobial Resistance Team, part of the Clinical and Environmental Microbiology Branch in the Division of Healthcare Quality Promotion, has a combined staff experience of more than 25 years of working with CLSI. Efforts of the previous leaders of the team, Drs. Clyde Thornsberry and Fred Tenover, were fundamental in establishing the relationship between CDC and the CLSI Subcommittee on Antimicrobial Susceptibility Testing and both remain very involved in CLSI Subcommittee activities. Jana Swenson has been involved with the subcommittee since 1990 as both a member and a chair of multiple working groups including the Text and Tables Working Group, which is responsible for text in three of CLSI’s most widely used documents, M100, M7, and M2. Jean Patel also currently serves as a member of the subcommittee.

Patel, Swenson, and Wong presented their findings on the mupirocin resistance and carbapenemase studies at the June 15–17, 2008, meeting of the Subcommittee of Antimicrobial Susceptibility Testing. In collaboration with 17 testing sites in California, Illinois, Iowa, Maryland, Massachusetts, Nebraska, New York, North Carolina, Ohio, Oregon, Texas, and Canada, CDC presented data demonstrating that mupirocin resistance (presence of the mupirocin A, or mupA, gene) can be detected by disk diffusion or broth microdilution methods and that the Modified Hodge Test (MHT) can be used to detect carbapenemases, a new, emerging mechanism of antibiotic resistance. The group proposed quality control ranges for mupirocin testing methods and identified quality assessment strategies for the MHT.

As a result of these studies, the 2009 CLSI standard consensus reference documents M2 and M7 will include criteria for a topical agent, mupirocin, for the first time and provide guidance on carbapenemases detection. These documents are used by diagnostic laboratories to perform routine testing and to evaluate commercial devices, new agents, and systems.

Guided by the desire to improve the quality of patient and medical care, the Antimicrobial Resistance Team continues to address emerging antimicrobial resistance, guide clinical and reference laboratories, and promote the use of quality laboratory practices.

About the author

Betty Wong, MPH, CHES, is a researcher on the Antimicrobial Resistance Team, part of the Clinical and Environmental Microbiology Branch in the Division of Healthcare Quality Promotion, National Center for Preparedness, Detection, and Control of Infectious Diseases, and is a member of CDC’s Institutional Review Board.