Overview
Bacteriology laboratory interpretation assigns clinical-laboratory significance to culture and smear findings by integrating anatomic site, organism quantity, culture purity, host modifiers, and method limits.
Classification
| Judgment | Meaning | Lab emphasis |
|---|---|---|
| Pathogen-likely | Evidence supports disease role | Full ID ± AST per SOP |
| Colonizer | Expected/residence flora pattern | Limit workup per site rules |
| Contaminant | Likely introduced artifact | Policy-limited workup; careful wording |
| Uncertain | Insufficient axes aligned | Escalate / correlate |
Morphologic Features
Direct smear inflammatory cells versus epithelial contamination cues feed interpretation alongside colony quantity grades.
Laboratory Characteristics
- Site-specific workup tables
- Quantity notation standards
- Approved report comments
- Blood-culture set/bottle documentation
Reference Intervals
Urine colony-count cutoffs, respiratory quality scores, and blood-culture contamination definitions are institutional, verify current SOP; do not treat any single published cutoff as universal.
Clinical and Laboratory Significance
Interpretation determines which isolates receive full identification/AST handoff and how results are framed for clinicians.
Differential Considerations
Separate colonization, contamination, and infection evidence using reproducibility and host risk, especially for common skin flora species.
Comparison Tables
Significance cues
| Finding | Lean pathogen | Lean contaminant/colonizer |
|---|---|---|
| CoNS blood | Multiple sets + high-risk host | Single bottle, low-risk host |
| Mixed wound flora | One dominant organism in deep specimen | Equal light skin flora mix |
| LF GNR urine | Count above local threshold | Low count / poor collection |
Classification Frameworks
Not applicable.
Laboratory Notes
- Hedge institutional significance and critical lists
- Do not auto-pathogen every famous species name
- No antimicrobial dosing in interpretive comments
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
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