Overview
Mechanism of action describes the cellular process an antimicrobial targets. In AST education it supports panel literacy; reportable categories still require standardized phenotypic testing.
Classification
| MOA family | Example agents (illustrative) | AST note |
|---|---|---|
| Cell wall | β-lactams, glycopeptides | Inoculum/media critical |
| Protein synthesis | Aminoglycosides, macrolides, tetracyclines | Atmosphere/media may vary |
| Nucleic acid | Fluoroquinolones, rifamycins | Endpoint reading per SOP |
| Folate pathway | Trimethoprim–sulfonamides | Trailing endpoints, follow SOP |
| Membrane | Polymyxins (specialized) | Method/QC often specialized |
Morphologic Features
Not morphologic. Interpret zones/MICs only after correct inoculum density and approved medium.
Laboratory Characteristics
- MOA informs menu expectations
- 0.5 McFarland-equivalent inoculum (confirm SOP)
- Approved medium ± supplements
- Agent-specific reading rules
- QC within institutional ranges
Reference Intervals
Do not memorize universal numeric breakpoints or QC ranges from secondary sources. Verify the laboratory’s currently adopted CLSI or EUCAST edition and local QC tables.
Clinical and Laboratory Significance
MOA knowledge helps anticipate which agents appear for an organism group. Only validated phenotypes support clinical use of categories.
Differential Considerations
Differentiate expected inactivity (wrong organism/target) from technical artifact (heavy inoculum, wrong media, degraded disk) and from true resistance mechanisms.
Comparison Tables
MOA vs method troubleshooting
| Observation | First check | Avoid |
|---|---|---|
| Unexpectedly small zones | Inoculum density, media, QC | MOA “failure” narrative |
| QC out of range | Stop release; troubleshoot method | Releasing patient AST |
| Trailing/haze | SOP reading rule for that agent | Guessing a category |
Classification Frameworks
Not applicable.
Laboratory Notes
- No drug selection or dosing from MOA teaching
- Hedge breakpoints and QC as institutional
- Emphasize inoculum, media, reading, QC over theory alone
References
Authoritative textbooks, guidelines, and reviews supporting this reference entry. Verify reference intervals, critical limits, and reflex criteria against institutional protocols and current guideline editions.
Textbooks
- Forbes BA, Sahm DF, Weissfeld AS. Bailey & Scott's Diagnostic Microbiology. 15th ed. Elsevier; 2020.
- Mahon CR, Lehman DC, Manuselis G. Textbook of Diagnostic Microbiology. 6th ed. Elsevier; 2018.
- Carroll KC, Hobden JA, Miller S, et al. Jawetz, Melnick, & Adelberg's Medical Microbiology. 28th ed. McGraw-Hill; 2019.
- Murray PR, Rosenthal KS, Pfaller MA. Medical Microbiology. 9th ed. Elsevier; 2021.
CLSI and Professional Guidelines
- Clinical and Laboratory Standards Institute. Performance Standards for Antimicrobial Susceptibility Testing. CLSI document M100 (verify current edition and institutional adoption).
- Centers for Disease Control and Prevention / NIH. Biosafety in Microbiological and Biomedical Laboratories (BMBL). Current edition (verify institutional adoption).
Frequently Asked Questions
Common questions about using this Mechanisms of Action foundational topics Medical Laboratory Library reference in Medical Laboratory Science education.
What is the Mechanisms of Action laboratory reference?
Mechanisms of Action is a Foundational Topics entry in the LabPedia Medical Laboratory Library, written for Medical Laboratory Science reference lookup.
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