CLSI Publishes Performance Standards for Antimicrobial Susceptibility Testing; June 2010 Update

WAYNE, PA–(Marketwire – July 20, 2010) – Clinical and Laboratory Standards Institute (CLSI) recently published “Performance Standards for Antimicrobial Susceptibility Testing; Twentieth Informational Supplement (June 2010 Update)” (M100-S20-U).

This update includes:

• New interpretive criteria for doripenem for Enterobacteriaceae
• Revised interpretive criteria for ertapenem, imipenem, and meropenem for Enterobacteriaceae
• Guidance for use of the modified Hodge test (MHT) with revised interpretive criteria for carbapenems

Jean B. Patel, PhD, D(ABMM), Deputy Director, Office of Antimicrobial Resistance, Centers for Disease Control and Prevention, and member of the subcommittee that developed the update, says, “Carbapenemase-producing Enterobacteriaceae are a significant infection control concern, and rapid laboratory detection of isolates that may carry these resistance mechanisms is an important step in preventing transmission. Since these isolates will test nonsusceptible (ie, intermediate or resistant) to one or more of the carbapenem agents using the revised breakpoints, it will be easier for laboratories to identify these isolates and to report their findings to hospital infection preventionists.”

Michael N. Dudley, PharmD, FCCP, FIDSA, Senior Vice President, Research & Development and Chief Scientific Officer, Mpex Pharmaceuticals, Inc., and member of the subcommittee that developed the update, agrees, “It was important to provide further direction to laboratories on detection of isolates with reduced susceptibility to carbapenems. Unfortunately, there are no reliable clinical studies that allow assessment of the clinical response to treatment of carbapenem-producing strains to carbapenem antimicrobial agents. However, studies in animal models indicate that the minimal inhibitory concentration (MIC) is the best predictor of antibacterial effects. The new MIC breakpoints, coupled with US Food and Drug Administration (FDA)-approved dosage regimens used frequently in the clinic, provide for a better probability of attaining pharmacokinetic/pharmacodynamic exposures associated with antibacterial effects in vivo. The new intermediate and resistant breakpoints for carbapenems also ‘capture’ a majority of isolates that produce carbapenemases that can be confirmed using the MHT, if needed.”

He adds, “This new update will help laboratories improve quality and provide timelier reporting of susceptibility results.”

Tracy Dooley, MLT(ASCP), CLSI Standards Administrator, explains the importance of publishing a midyear update to the well-known annual antimicrobial susceptibility testing (AST) breakpoints, saying, “In an effort to disseminate information to users in a timelier manner, the Subcommittee on AST decided to publish a midyear M100 supplement with the new/revised carbapenem interpretive criteria for Enterobactericeae. This midyear publication allows laboratories to begin to initiate the implementation of these changes. One of the benefits of the new interpretive criteria is that nearly all carbapenemase-producing isolates will test nonsusceptible to one or more carbapenems. This alleviates the need to perform initial screening and confirmatory testing (MHT) for routine patient testing. Historically, each complete blood count (CBC) instrument/reagent manufacturer developed its unique approaches to system validation and performance claims. This standard will help create better standardization among manufacturers, as well as assist practicing laboratories in developing consistent testing.”

The tables in this M100-S20 June 2010 Update are to replace Tables 2A and 2A-S2 in
Performance Standards for Antimicrobial Susceptibility Testing; Twentieth Informational Supplement (M100-S20) (January 2010). For other tables referenced in this update, please see M100-S20 (January 2010).

CLSI is a volunteer-driven, membership-supported, nonprofit organization dedicated to developing standards and guidelines for the health care and medical testing community through a consensus process that balances the perspectives of industry, government, and the health care professions. For additional information on CLSI, visit the CLSI website at www.clsi.org or call 610.688.0100.

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