Updating antimicrobial susceptibility testing: present and future relevance.

1. Cynthia B. Schofield, MPH, MT (CAMT)[⇑][1] 1. VA San Diego Healthcare System (retired), San Diego, CA 1. Address for Correspondence: Cynthia B. Schofield, MPH, MT (CAMT), VA San Diego Healthcare System (retired), 7050 Weller St., San Diego, CA, (858) 450-9651, cschofield{at}san.rr.com 1. Discuss the “state of the art” of antimicrobial susceptibility testing (AST) from the National Laboratory System (NLS) surveys. 2. Summarize the critical factors in disk diffusion and broth dilution testing. 3. Explain the potential sources of error inherent in AST methods. 4. Discuss breakpoints and reasons for microbiologists concern. 5. Discuss the controversy surrounding AST interpretive values. 6. Compare and contrast AST and molecular assays for routine laboratory use. State of the Art Testing methods and reporting of results vary widely among clinical, reference and public health laboratories. Accordingly, institutional size and resources dictate both antimicrobial susceptibility testing (AST) needs and the cost effectiveness of test methods. Results of evaluations from 102 laboratories by the National Laboratory System (NLS) between 2001 and 2005 proved fewer than 50% of these laboratories published antibiograms of local resistance patterns and fewer than 50% adhered to the guidelines and standards established by the Clinical and Laboratory Standards Institute (CLSI). The effort to improve performance and adherence to CLSI standards and to assure rapid detection and reporting of antimicrobial resistance was undertaken by the NLS. NLS consists a group of microbiologists from the University of Washington, the University of California at Los Angeles and the Centers for Disease Control and Prevention (CDC). The NLS investigators surveyed the labs in 2001 and 2005 to determine the effect of 2003 and 2004 interventions. The interventions included AST workshops according to CLSI guidelines. Investigators trained local faculty in the use of a CDC AST self study and distributed free CLSI documents. Web sites and teleconferences were instituted as educational supplements. The 2001 assessment compared case studies of AST performance when testing Enterococcus sp., methicillin-resistant S. aureus (MRSA) and S. pneumoniae among the 102 laboratories. In a 2002 survey, changes in case studies from the previous year were noted and recorded. Changes over a period of 5 years were tabulated by the surveys (2001 to 2005) in the… ABBREVIATIONS: AST-antimicrobial susceptibility testing; NLS-National Laboratory System; CDC-Center for Disease Control and Prevention; CLSI-Clinical and Laboratory Standards Institute; MIC-minimal inhibitory concentration; MH-Mueller-Hinton; CAP-College of American Pathologists; PK/PD-pharmacokinetic/pharmacodynamics; UTI-urinary tract infection; CSF-cerebrospinal fluid; FDA-Food and Drug Administration; EUCAST-European Committee on Antimicrobial Susceptibility Testing; AUC-area under the concentration curve; PCR-polymerase chain reaction; HAI-hospital-associated infection; CAI-community-associated infection; MRSA-methicillin-resistant Staphylococcus aureus ; VRE-vancomycin-resistant Enterococcus sp.; MTB- Mycobacterium tuberculosis ; ESBL-extended-spectrum beta lactamase; KPC- Klebsiella pneumoniae carbapenem-resistant; MDR-multi-drug resistant. 1. Discuss the “state of the art” of antimicrobial susceptibility testing (AST) from the National Laboratory System (NLS) surveys. 2. Summarize the critical factors in disk diffusion and broth dilution testing. 3. Explain the potential sources of error inherent in AST methods. 4. Discuss breakpoints and reasons for microbiologists concern. 5. Discuss the controversy surrounding AST interpretive values. 6. Compare and contrast AST and molecular assays for routine laboratory use. [1]: #corresp-1