Quality Control in Microbiology

Quality control in microbiology is the system of checks that ensures laboratory results are accurate, reliable, and reproducible. It spans verifying that media, reagents, and instruments perform correctly, using control strains, and participating in external proficiency testing, so that a reported result reflects the patient rather than a laboratory error.

Definition

Quality control in microbiology is the set of procedures and standards used to monitor and verify the performance of media, reagents, instruments, and personnel so that test results are accurate, reproducible, and traceable.

Scope

The topic covers internal quality control (control organisms, media and reagent checks, instrument verification), external quality assessment and proficiency testing, and the standards and competency practices that underpin them. It is framed as a methodological subject and does not provide testing or treatment instructions for individual patients.

Core questions

• How does a laboratory verify that its media, reagents, and instruments perform correctly?
• What role do control strains and proficiency testing play?
• How do standards support reproducible and comparable results across laboratories?

Key concepts

• Internal quality control
• Reference (control) strains
• Media and reagent quality control
• Instrument verification and calibration
• External quality assessment
• Proficiency testing
• Standards and competency assessment

Mechanisms

Laboratories run defined control organisms and reagent checks so that each test system gives expected results before patient specimens are reported; antimicrobial susceptibility testing, for example, uses reference strains with known expected ranges to confirm that the system is performing within tolerance (CLSI M100). Instruments are verified and calibrated, and lot-to-lot performance of media and reagents is monitored. External quality assessment and proficiency testing send unknown samples to laboratories so their results can be compared against peers and a reference answer, revealing systematic errors. Reference texts and utilization guidance frame these controls as integral to producing trustworthy results (Jorgensen 2015; Baron 2013).

Clinical relevance

Quality control determines whether a microbiology result can be trusted; lapses can produce erroneous identifications or susceptibility results with downstream consequences. Understanding these systems supports critical appraisal of laboratory data. The topic describes how result reliability is assured and is not a basis for individual diagnostic or treatment decisions.

Evidence & guidelines

Consensus standards specify quality-control procedures and expected ranges for laboratory testing, including reference-strain controls for antimicrobial susceptibility testing (CLSI M100); reference texts and utilization guidance describe internal quality control and proficiency testing as part of reliable practice (Jorgensen 2015; Baron 2013).

History

Laboratory quality assurance developed alongside the standardization of clinical microbiology, with formal control strains, reagent checks, and external proficiency testing becoming established components of accredited practice and codified in consensus standards (CLSI M100; Jorgensen 2015).

Seminal works

• baron-2013
• jorgensen-2015

Frequently asked questions

What is the difference between internal quality control and proficiency testing?

Internal quality control uses known control strains and reagent checks within the laboratory to verify daily performance, while proficiency testing (external quality assessment) compares the laboratory's results on unknown samples against peers and a reference answer.

Why are control strains used in susceptibility testing?

Reference strains have established expected results, so testing them confirms that the test system is performing within accepted tolerances before patient results are reported.