A report from the committee on microbroth dilution antimicrobial susceptibility testing

Abstract

In 1968, the Japanese Society of Chemotherapy (JSC) established an agar dilution method for MIC determinations of aerobic bacteria [1]. In 1979, the JSC established an agar dilution method for MIC determinations of anaerobic bacteria. Furthermore, a revision of the agar dilution standard was made in 1980, and this served as the standard method for MIC determinations for an extensive period of time in Japan. In 1990, the committee established a standard microbroth dilution method for MIC determinations. This method was modified in 1992 for fastidious aerobic and anaerobic bacteria [2]. In the development of standards for antimicrobial susceptibility testing, there has been a movement to incorporate pharmacologic as well as clinical considerations with respect to in vitro antimicrobial susceptibility interpretations. This trend reflects the need to respond to the emergence and spread of resistant microorganisms as well as a greater understanding of pharmacokinetics and pharmacodynamics and how it relates to improved patient outcome. The Clinical Laboratory Standards Institute (CLSI) and the European Committee on Antimicrobial Susceptibility (EUCAST) are among the professional organizations that proactively revise antimicrobial susceptibility testing on a regular basis. JSC has also been revising its standards. In 2007, the agar dilution method was revised. After the exclusion of selected organisms from the CLSI agar dilution standard, this method was adopted by the JSC [3]. With respect to revising the standard method for microbroth dilution antimicrobial susceptibility testing, a committee chaired by Keizo Yamaguchi was formed in January 2008. The subcommittee’s first task was to critically examine the methods for the antimicrobial susceptibility testing of Haemophilus influenzae. Although JSC and CLSI microbroth dilution methods both use a Mueller– Hinton base, the supplements differ. This difference had raised concerns among some Japanese clinical microbiology professionals that there were many issues with the CLSI method with respect to reported difficulties in measuring endpoints and the poor growth of some strains. Our first action was to send questionnaires to the members of the JSC and the Japanese Society for Clinical Microbiology to better understand the technical problems experienced in clinical microbiology laboratories regarding microbroth dilution testing of H. influenzae. From the responses to the questionnaire, it was clear that a major problem in routine testing was the poor growth of Members of the Microdilution Susceptibility Standards Committee: committee chairperson: Keizo Yamaguchi, committee members: Yoichi Hirakata, Intetsu Kobayashi, Masanari Ikedo, Akira Ohno.