M31-A3
Vol. 28 No. 8
Replaces M31-A2
Vol. 22 No. 6
Performance Standards for Antimicrobial
Disk and Dilution Susceptibility Tests for
Bacteria Isolated From Animals; Approved
Standard—Third Edition
940 West Valley Road Suite 1400 Wayne, PA 19087 USA PHONE 610.688.0100
FAX 610.688.0700 E-MAIL: customerservice@clsi.org WEBSITE: www.clsi.org ISBN 1-56238-659-X
(Formerly NCCLS)
This document provides the currently recommended techniques for antimicrobial agent
disk and dilution susceptibility testing, criteria for quality control testing, and interpretive
criteria for veterinary use.
A standard for global application developed through the Clinical and Laboratory
Standards Institute consensus process.
(Formerly NCCLS)
Volume 28 Number 8
M31-A3
ISBN 1-56238-659-X
ISSN 0273-3099
Performance Standards for Antimicrobial Disk and Dilution
Susceptibility Tests for Bacteria Isolated From Animals; Approved
Standard—Third Edition
Jeffrey L. Watts, PhD, RM(AAM)
Thomas R. Shryock, PhD
Michael Apley, DVM, PhD
Donald J. Bade
Steven D. Brown, PhD
Jeffrey T. Gray, PhD
Henry Heine, PhD
Rob P. Hunter, MS, PhD
Dik J. Mevius, DVM, PhD
Mark G. Papich, DVM, MS
Peter Silley, PhD
Gary E. Zurenko, MS
Abstract
If the susceptibility of a bacterial pathogen to antimicrobial agents cannot be predicted based on the identity of the organism
alone, in vitro antimicrobial susceptibility testing of the organism isolated from the disease processes in animals is indicated.
Susceptibility testing is particularly necessary in those situations where the etiologic agent belongs to a bacterial species for
which resistance to commonly used antimicrobial agents has been documented, or could arise.
A variety of laboratory techniques can be used to measure the in vitro susceptibility of bacteria to antimicrobial agents. Clinical
and Laboratory Standards Institute document M31-A3—Performance Standards for Antimicrobial Disk and Dilution
Susceptibility Tests for Bacteria Isolated From Animals; Approved Standard—Third Edition describes the standard agar disk
diffusion method, as well as standard broth dilution (macrodilution and microdilution) and agar dilution techniques. It also
includes a series of procedures designed to standardize test performance. The performance, applications, and limitations of the
current CLSI-recommended methods are described.
The tabular information in this document presents the most current information for drug selection, interpretation, and quality
control. In an increasing number of compounds where veterinary-specific interpretive criteria are not available, human
interpretive criteria are used. As more veterinary-specific information becomes available, these changes will be incorporated into
future revisions of this document.
Clinical and Laboratory Standards Institute (CLSI). Performance Standards for Antimicrobial Disk and Dilution Susceptibility
Tests for Bacteria Isolated From Animals; Approved Standard—Third Edition. CLSI document M31-A3 (ISBN 1-56238-659-X).
Clinical and Laboratory Standards Institute, 940 West Valley Road, Suite 1400, Wayne, Pennsylvania 19087-1898 USA, 2008.
The Clinical and Laboratory Standards Institute consensus process, which is the mechanism for moving a document through two or more levels
of review by the health care community, is an ongoing process. Users should expect revised editions of any given document. Because rapid
changes in technology may affect the procedures, methods, and protocols in a standard or guideline, users should replace outdated editions
with the current editions of CLSI/NCCLS documents. Current editions are listed in the CLSI catalog and posted on our website at
www.clsi.org. If your organization is not a member and would like to become one, and to request a copy of the catalog, contact us at:
Telephone: 610.688.0100; Fax: 610.688.0700; E-Mail: customerservice@clsi.org; Website: www.clsi.org
(Formerly NCCLS)
Volume 28
M31-A3
Contents
Abstract ....................................................................................................................................................i Committee Membership........................................................................................................................ iii Foreword ................................................................................................................................................ix 1 Scope .......................................................................................................................................... 1 2 Introduction ................................................................................................................................ 1 3 Definitions ................................................................................................................................. 2 4 Indications for Performing Susceptibility Testing ..................................................................... 5 4.1 5 Selection of Antimicrobial Agents............................................................................................. 6 5.1 5.2 5.3 5.4 5.5 5.6 6 Source ......................................................................................................................... 25 Weighing Antimicrobial Agent Powders .................................................................... 25 Preparing Stock Solutions ........................................................................................... 27 Number of Concentrations Tested .............................................................................. 27 Agar Dilution Procedure .......................................................................................................... 27 9.1 9.2 10 Indications for Performing Broth and Agar Dilution Susceptibility Tests ................. 25 Antimicrobial Agents ............................................................................................................... 25 8.1 8.2 8.3 8.4 9 Equivalent MIC Breakpoints ...................................................................................... 13 Methodologies ............................................................................................................ 13 Streptococcus spp. ...................................................................................................... 19 Pasteurella multocida and Mannheimia haemolytica ................................................. 20 Other Organisms ......................................................................................................... 20 Campylobacter jejuni and Related Species................................................................. 20 Anaerobic Organisms ................................................................................................. 21 Detection of Resistant Staphylococci ......................................................................... 21 Detection of Resistant Enterococci ............................................................................. 23 Broth and Agar Dilution Susceptibility Testing ...................................................................... 24 7.1 8 Nonproprietary Names .................................................................................................. 7 Selection Guidelines ..................................................................................................... 7 Antimicrobial Classes ................................................................................................... 7 Guidelines for Routine Reporting ............................................................................... 11 Guidelines for Selective Reporting ............................................................................. 11 Interpretive Categories ................................................................................................ 12 Disk Diffusion Susceptibility Tests ......................................................................................... 13 6.1 6.2 6.3 6.4 6.5 6.6 6.7 6.8 6.9 7 Limitations of Disk Diffusion and Dilution Methods ................................................... 5 Reagents and Materials ............................................................................................... 28 Agar Dilution Testing of C. jejuni .............................................................................. 31 Broth Dilution Procedure ......................................................................................................... 32 10.1 10.2 10.3 Broth Medium ............................................................................................................. 32 Cation Adjustments..................................................................................................... 32 Preparing and Storing Diluted Antimicrobial Agents ................................................. 33 v
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Contents (Continued)
10.4 10.5 10.6 10.7 11 Broth Dilution Susceptibility Testing of Fastidious Organisms .............................................. 35 11.1 11.2 11.3 11.4 11.5 12 Purpose ....................................................................................................................... 39 QC Responsibilities .................................................................................................... 40 Suggested Reference Strains ....................................................................................... 41 Disk Diffusion Tests ................................................................................................... 43 Frequency of QC Testing (also refer to Appendix B) ................................................. 43 Dilution Susceptibility Tests ....................................................................................... 45 Daily Testing............................................................................................................... 46 Weekly Testing ........................................................................................................... 46 Corrective Action ........................................................................................................ 46 Specific Antimicrobial Resistance Tests.................................................................................. 48 15.1 15.2 15.3 15.4 16 Penicillin-Ampicillin Resistance ................................................................................ 39 Vancomycin Resistance .............................................................................................. 39 High-Level Aminoglycoside Resistance..................................................................... 39 QC Guidelines.......................................................................................................................... 39 14.1 14.2 14.3 14.4 14.5 14.6 14.7 14.8 14.9 15 Methicillin/Oxacillin Resistance ................................................................................. 37 Oxacillin Screening Plates .......................................................................................... 38 Reduced Susceptibility to Vancomycin ...................................................................... 38 Detection of Resistant Enterococci .......................................................................................... 39 13.1 13.2 13.3 14 P. multocida and M. haemolytica ............................................................................... 35 Broth Microdilution Testing of H. somni and A. pleuropneumoniae ......................... 35 Broth Microdilution Testing of Campylobacter spp. .................................................. 36 Streptococci and Listeria spp. ..................................................................................... 36 Staphylococcus hyicus ................................................................................................ 37 Detection of Resistant Staphylococci ...................................................................................... 37 12.1 12.2 12.3 13 Standardizing Inoculum for Broth Dilution Testing ................................................... 34 Inoculating Broth ........................................................................................................ 34 Incubation ................................................................................................................... 35 Interpreting Results ..................................................................................................... 35 Purpose ....................................................................................................................... 48 β-Lactamase Tests ...................................................................................................... 48 Selecting a β-Lactamase Test ..................................................................................... 48 Detection of Extended-Spectrum, β-Lactamase-Producing Enterobacteriaceae ........ 48 Cumulative Antimicrobial Susceptibility Profile ..................................................................... 49 References ............................................................................................................................................. 50 Appendix A. Antimicrobial Susceptibility QC Record......................................................................... 52 Appendix B1. Disk Diffusion Daily QC Testing Protocol ................................................................... 53 Appendix B2. Disk Diffusion Weekly QC Testing Protocol ................................................................ 54 Appendix C1. Aerobic Dilution Daily QC Testing Protocol ................................................................ 55 Appendix C2. Aerobic Dilution Weekly QC Testing Protocol............................................................. 56 vi
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Contents (Continued)
Appendix D1. Disk Diffusion QC Troubleshooting Guide .................................................................. 57 Appendix D2. MIC QC Troubleshooting Guide ................................................................................... 60 Table 1. Antimicrobial Agents That Could Be Considered for Routine Testing by Veterinary
Microbiology Laboratories ................................................................................................................... 63 Table 2. Zone Diameter Interpretive Standards and Minimal Inhibitory Concentration (MIC)
Breakpoints for Veterinary Pathogens .................................................................................................. 65 Table 3. Culture Collection Numbers for Organisms Used for QC of Antimicrobial Susceptibility
Tests ...................................................................................................................................................... 73 Table 4. Acceptable QC Ranges of Antimicrobial Disk Susceptibility Test Zone Diameters (mm)
for Reference Strains on Mueller-Hinton Agar (Except Where Noted)................................................ 74 Table 5. Acceptable QC Ranges of MICs for Broth Microdilution (µg/mL) for Reference Strains..... 76 Table 5A. Acceptable QC Ranges of MICs (μg/mL) for the Agar Dilution Method of Testing
Campylobacter jejuni ATCC® 33560 ................................................................................................... 78 Table 5B. Proposed QC Ranges of MICs (μg/mL) for the Broth Microdilution Susceptibility
Method of Testing Campylobacter jejuni ATCC® 33560..................................................................... 79 Table 5C. Proposed QC Ranges of MICs (µg/mL) for Anaerobic Reference Strains Using Agar
Dilution ................................................................................................................................................. 80 Table 5D. Proposed QC Ranges of MICs (µg/mL) for Anaerobic Reference Strains Using Broth
Microdilution ........................................................................................................................................ 81 Table 6. Acceptable QC Ranges for Histophilus somni and Actinobacillus pleuropneumoniae .......... 82 Table 7. Standard Methods for Susceptibility Testing of Some Fastidious and Special Problem
Veterinary Pathogens ............................................................................................................................ 83 Table 8. Solvents and Diluents for Preparation of Stock Solutions of Antimicrobial Agents
Requiring Solvents Other Than Water .................................................................................................. 84 Table 9A. Screening and Confirmatory Tests for Extended-Spectrum β-lactamases (ESBLs) in
Klebsiella pneumoniae, K. oxytoca, Escherichia coli, and Proteus mirabilis (Zone Diameter) ........... 85 Table 9B. Screening and Confirmatory Tests for ESBLs in Klebsiella pneumoniae, K. oxytoca,
Escherichia coli, and Proteus mirabilis (MIC) ..................................................................................... 86 Table 9C. Screening Tests for Oxacillin Resistance and Reduced Susceptibility to Vancomycin in
Staphylococcus aureus .......................................................................................................................... 87 Table 9D. Disk Diffusion Test for Prediction of mecA-Mediated Resistance in Staphylococci .......... 88 Table 9E. Disk Diffusion Screening Tests for High-Level Aminoglycoside Resistance (HLAR) ....... 89 vii
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Contents (Continued)
Table 9F. MIC Screening Tests for High-Level Aminoglycoside Resistance (HLAR) and
Vancomycin Resistance in Enterococcus spp. ...................................................................................... 90 Glossary 1. Antimicrobial Class, Antimicrobial Subclass Designation, Antimicrobial Agents, and
Antimicrobial Resistance Mechanisms ................................................................................................. 91 Glossary 2. Abbreviations for Antimicrobial Agents Incorporated Into Disks or Susceptibility
Panels ................................................................................................................................................. 94 Summary of Comments and Subcommittee Responses ........................................................................ 96 The Quality Management System Approach ........................................................................................ 98 Related CLSI Reference Materials ....................................................................................................... 99 viii
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Foreword
This revision of the M31 standard represents a continuation of the collective efforts of the Subcommittee
on Veterinary Antimicrobial Susceptibility Testing (VAST) to produce a globally useful consensus
document for standardized in vitro susceptibility testing of veterinary pathogens. The subcommittee has
worked diligently to improve M31-A2—Performance Standards for Antimicrobial Disk and Dilution
Susceptibility Tests for Bacteria Isolated from Animals; Approved Standard—Second Edition primarily
by incorporating relevant updates derived from CLSI documents M2 and M7,1,2 as well as referencing
other relevant CLSI documents. The subcommittee recognizes the ongoing CLSI efforts that are
necessary to maintain CLSI documents M2 and M71,2 as “state of the art,” and expresses its appreciation
to the Subcommittee on Antimicrobial Susceptibility Testing for its contributions. In addition, it is also
appropriate to acknowledge the users of M31-A2 for their continued support and application of the
standard in their daily work routine. The user community is encouraged to demonstrate responsible
application of the CLSI methods when publishing work in peer-reviewed journals.
Global events and perceptions regarding the use of antimicrobial agents in animals have placed even more
importance on the essential role of antimicrobial susceptibility testing of bacteria isolated from animals.
For example, Judicious Use Guidelines (consensus directions for the appropriate use of antimicrobial
agents in animals) have been developed worldwide by veterinary societies, food animal production
organizations, government agencies, and international groups for both food and companion animals that
emphasize the critical need for obtaining susceptibility data using standardized test methods and
interpretive criteria. M31-A3 was updated to help meet these needs. Additionally, with an increased
emphasis on national “resistance surveillance” programs, the use of a standardized antimicrobial
susceptibility testing methodology and quality control (QC) provides a means to harmonize testing across
national boundaries to facilitate data comparisons. As a first step toward worldwide applications of
susceptibility testing using CLSI methods, a separate section lists QC strain entries in various
international repositories. A workflow sheet for QC testing and a troubleshooting checklist are now
available that should aid laboratories to track their performance for increased proficiency. Development
of specific test methods and QC values for several antimicrobial agents effective against Campylobacter
have also been developed, with the expectation that they will contribute to improved surveillance efforts.
Several additional antimicrobial agents have been reviewed since the previous edition of the document
and have received veterinary-specific interpretive criteria approval from the subcommittee. M31-A3
features these new antimicrobial agents in Table 1, Group A (Veterinary-Specific Interpretive Criteria,
Primary Test and Report). Further revisions were made to designate CLSI Approved Human Interpretive
Criteria, Primary Test, Selectively Report (Group B); No Veterinary Species Specific- or Human-Specific
Interpretive Criteria, Primary Test, Selectively Report (Group C); and Supplemental “AMDUCA-use”
(US Animal Medicinal Drug Use Clarification Act) products, Selectively Test, Selectively Report (Group
D). Additionally, refinements to definitions for “susceptible” and “resistant” designations are now
included. Using the principles for breakpoint establishment, several older, generic antimicrobial agents
have had veterinary-specific breakpoints set. The user should be aware that, while M31 is primarily
derived from CLSI documents M2 and M7,1,2 which are “human” documents, this version incorporates
more veterinary-specific information than before, although there is still ample opportunity for expansion.
This standard should not be considered a static document because it will change as additional methods for
testing veterinary pathogens become available, and in response to changes in antimicrobial agent usage in
veterinary medicine. The subcommittee is committed to making every effort to incorporate the latest
information into future versions of this standard.
The CLSI Subcommittee on VAST believes the document also serves as an educational resource. The
subcommittee believes diagnostic laboratory personnel, veterinarians, students, and allied professionals
will benefit from this document. Thus, a glossary of antimicrobial agents and resistance mechanisms, and
a listing of antimicrobial resistance tests have been assembled for the convenience of investigators
interested in this area.
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The subcommittee anticipates that, as a result of the efforts of several new working groups, additional
fastidious pathogens will be included in future editions, such as the intestinal spirochetes, Haemophilus
parasuis, and mycoplasmas. Additionally, the inclusion of antimicrobial agents not currently marketed in
the United States is welcomed for future editions, with the goal of making this document as globally
useful as possible. A new working group within the subcommittee has been formed to address this need.
As mentioned before, the inclusion of international entries in culture collections of QC strains is viewed
as just the first step in this process, so leading laboratories might begin to use CLSI methods and compare
them with their own national methods. Perhaps the most important future revision will be shifting
antimicrobial agents from Table 1, Group C or B, to A. Because approvals of new antimicrobial agents
for veterinary medicine are foreseen to be a rare event, the subcommittee will begin to shift its focus to
the Generics Working Group to develop data in conformance with the M37 guideline to continue to
advance generic drugs into Group A. I encourage and welcome input regarding ways to improve the
document.
In closing, I recognize the tremendous efforts of the Subcommittee on Veterinary Antimicrobial
Susceptibility Testing in producing this revised document. I would like to particularly acknowledge the
individual members of the Editorial Working Group. Their willingness to sacrifice significant amounts of
their personal time for the editing process and to address controversial topics demonstrates a real
commitment to the CLSI process and the advancement of the veterinary and microbiology professions. I
thank Jo Abraham, Jeff Gray, Janine Matlak, Maria Traczewski, Ching Ching Wu, and Steve Yan. Of
particular note are Bob Walker, Pat McDermott, and Tom Fritsche, for their work in developing QC
values for susceptibility testing of Campylobacter.
Thomas R. Shryock, PhD
Subcommittee on Veterinary
Antimicrobial Susceptibility Testing
Mission Statement
To develop and promote performance standards and interpretive criteria for in vitro antimicrobial
susceptibility testing of bacteria isolated from animals.
Key Words
Agar diffusion, agar dilution, antimicrobial agent, antimicrobial susceptibility, broth dilution,
susceptibility testing, veterinary
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M31-A3
Performance Standards for Antimicrobial Disk and Dilution Susceptibility
Tests for Bacteria Isolated From Animals; Approved Standard—Third Edition
1
Scope
This document provides veterinary diagnostic laboratories with currently recommended antimicrobial
agent disk and dilution susceptibility test methods for bacteria isolated from animals; criteria for quality
control (QC) testing; and interpretive criteria. The interpretive criteria are intended only to support
therapeutic label claims for animal antimicrobial agent use and do not apply to label claims for disease
prevention or performance enhancement. Additionally, the document provides a brief overview of the
various antimicrobial classes and mechanisms of resistance to them, including specific tests for
antimicrobial resistance.
In order to have a positive impact on clinical outcomes, help maintain antimicrobial effectiveness, assist
clinicians in using antimicrobials safely, and minimize selection of resistant pathogens, laboratories must
use a standardized, well-defined method for performing antimicrobial susceptibility testing (AST). A
critical component of an AST method is the relationship between the test outcome and clinical outcome
following treatment of the animal. In other words, an isolate yielding a susceptible AST result would be
expected to respond clinically to that agent at the appropriate dosages while an AST result of resistant
would imply that the treatment would fail. The purpose of the test method is not to mimic in vivo
conditions; rather, it is to establish a method that provides reproducible results. Therefore, to ensure the
generation of accurate, reproducible results when performing ASTs on veterinary pathogens, laboratories
must adhere to a standard, well-defined method that includes the appropriate QC information. The M31A3 document is predicated on providing AST methods that give accurate, reproducible, clinically relevant
results for veterinary pathogens. It is important to consider that the judicious use of antimicrobials in the
veterinary setting is directly related to the interpretive criteria associated with AST in that a given set of
interpretive criteria only applies to that specific antimicrobial and disease combination. It is also
important to note that the interpretive criteria in M31-A3 apply only if the laboratory has conducted
susceptibility testing according to the specific methods found in the documents.
To date, an increasing number of antimicrobial agents have established veterinary-specific interpretive
criteria. In most cases where veterinary-specific interpretive criteria are not established, human
interpretive criteria are used when appropriate (see CLSI documents M2, M7, and M111-3). The
veterinary-specific interpretive criteria have been established following M37, with particular attention
given to product label indications and directions as approved by regulatory authorities. As more
veterinary-specific information becomes available, changes in the listing of the agents will be
incorporated into future revisions of this document and associated supplements. AST of bacteria from
aquaculture environments has been advanced with the publication of two CLSI documents: M42 and
M49.4,5
2
Introduction
A variety of laboratory techniques can be used to measure the in vitro susceptibility of bacteria to
antimicrobial agents. These include disk diffusion as well as broth and agar dilution techniques. This
document includes a series of recommendations to help standardize the way these tests are performed.
The performance, applications, and limitations of the currently recommended methods are described.
Recommendations by the International Collaborative Study (ICS), as well as regulations established by
the US Food and Drug Administration and other regulatory agencies, have been reviewed and the
appropriate sections have been incorporated into this standard.6-8 This document describes current
methodology applicable to therapeutic uses of antimicrobial agents used in veterinary medicine for
diseases of animals, as described in Section 5. In recognition of the need for a global standard for AST for
©
Clinical and Laboratory Standards Institute. All rights reserved.
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M31-A3
bacteria isolated from animals, the Office International des Epizooties (OIE) published test method
guidelines in its Terrestrial Code that are consistent with those contained in this document (www.oie.int).
The need for globally harmonized test methods is essential if interlaboratory minimal inhibitory
concentration (MIC) or zone size data are to be compared in journals, Web postings, resistance
monitoring program reports, etc. The application of a single methodology also allows drug sponsors in
countries other than the United States to prepare data packages for presentation to the Veterinary AST
subcommittee by means of CLSI document M37.9
The subcommittee believes the development of new, or modified, in vitro testing procedures to determine
interpretive criteria to guide therapeutic uses of antimicrobial drugs in veterinary practice is not realistic
for two reasons:
First, there is no apparent variable that can be easily modified in the current procedure to reflect a key
factor that will correlate to in vivo efficacy. For example, any alteration in the inoculum (which might be
reflective of an initial low infectious dose early in an infectious process) would need to be validated with
efficacy studies in animals. Furthermore, redesigning the current methodology would require the
development of new QC guidelines; possibly disks with lowered antimicrobial content or extended
dilutions on MIC dilution panels.
Second, even if such a procedure were developed, how realistic is it to expect a laboratory to use it and
explain the outcome to a veterinarian or other client? As explained in the current edition of CLSI
document M37,9 interpretive criteria are based, in part, on the directions listed on the drug product label,
so any methods that were developed to support extra-label usage would place undue responsibility for
antibiotic decision-making on the laboratorian.
The subcommittee will continue to consider new developments in test methodologies and procedures, as
well as revisions to interpretive criteria for therapeutic agents. With respect to antimicrobial agents used
to promote or enhance food animal growth, the beneficial effects of antimicrobial agents can neither be
entirely ascribed to effects on the metabolic activities of microbial gut flora or suppression of “subclinical
disease,” nor correlated to physiological or immunological effects on the animal, so susceptibility testing
is of no value to predict an in vivo response. New in vitro techniques for prediction of clinical outcome
will be considered only when a better understanding of the mode of action of antimicrobial agents in this
situation becomes available.
3
Definitions
The selection of the most appropriate antimicrobial agents to test and report is a decision best made by
each laboratory in consultation with the pharmacy (where available) and veterinarians. The lists in Table
1 comprise agents of proven clinical efficacy for treatment of infections in that animal group, and which
show acceptable in vitro test performance. Agents listed are currently approved for treatment or control of
disease. Agents used for other purposes (such as prevention or growth promotion) are not listed, because
the correlation of AST for these uses cannot be established. Tests on selected agents can also be useful for
epidemiological or research purposes.
The subcommittee believes it is both appropriate and necessary to provide the rationale used to limit the
scope of this document to therapeutic and control uses of antimicrobial agents in veterinary medicine. For
the most part, these limitations reflect antimicrobial uses in livestock and poultry used for food
production, and do not necessarily apply to equine or small-animal medicine. Currently, antimicrobial
agents are approved by regulatory authorities for certain indications; treatment (ie, therapy), control, or
prevention of disease; or growth promotion. Inclusion of antimicrobial agents approved for use in
countries other than the United States is anticipated. The subcommittee has used the following definitions
of antimicrobial uses, which are consistent with current regulatory interpretations in its deliberations:
2
©
Clinical and Laboratory Standards Institute. All rights reserved.
Volume 28
M31-A3
Related CLSI Reference Materials∗
M2-A9
Performance Standards for Antimicrobial Disk Susceptibility Tests; Approved Standard—Ninth
Edition (2006). This standard contains recommended techniques, interpretive criteria, and quality control
parameters for disk susceptibility testing.
M6-A2
Protocols for Evaluating Dehydrated Mueller-Hinton Agar; Approved Standard—Second Edition
(2005). This standard contains procedures for evaluating production lots of Mueller-Hinton agar, and for the
development and application of reference media.
M7-A7
Methods for Dilution Antimicrobial Susceptibility Tests for Bacteria That Grow Aerobically; Approved
Standard—Seventh Edition (2006). This newly revised standard provides updated reference methods for the
determination of minimal inhibitory concentrations (MICs) for aerobic bacteria by broth macrodilution, broth
microdilution, and agar dilution.
M11-A7
Methods for Antimicrobial Susceptibility Testing of Anaerobic Bacteria; Approved Standard—Seventh
Edition (2007). This document provides reference methods for the determination of minimal inhibitory
concentrations (MICs) of anaerobic bacteria by agar dilution and broth microdilution.
M23-A2
Development of In Vitro Susceptibility Testing Criteria and Quality Control Parameters; Approved
Guideline—Second Edition (2001). This document addresses the required and recommended data needed for
the selection of appropriate interpretative standards and quality control guidelines for new antimicrobial
agents.
M37-A3
Development of In Vitro Susceptibility Testing Criteria and Quality Control Parameters for Veterinary
Antimicrobial Agents; Approved Guideline—Third Edition (2008). This document addresses the
recommended data needed for selection of appropriate interpretive standards and quality control guidelines for
new veterinary antimicrobial agents.
M39-A2
Analysis and Presentation of Cumulative Antimicrobial Susceptibility Test Data; Approved Guideline—
Second Edition (2005). This document describes methods for the recording and analysis of antimicrobial
susceptibility test data, consisting of cumulative and ongoing summaries of susceptibility patterns of
epidemiologically significant microorganisms.
M100-S18
Performance Standards for Antimicrobial Susceptibility Testing; Eighteenth Informational Supplement
(2008). This document provides updated tables for the Clinical and Laboratory Standards Institute (CLSI)
antimicrobial susceptibility testing standards M2-A9 and M7-A7.
∗
Proposed-level documents are being advanced through the Clinical and Laboratory Standards Institute consensus process;
therefore, readers should refer to the most current editions.
©
Clinical and Laboratory Standards Institute. All rights reserved.
99