Quality Control in Microbiology Notes

Quality Control in Microbiology

Learning Outcomes

• Review of lab techniques relevant to understanding quality control in microbiology.

ATCC (American Type Culture Collection) Organisms

• Purpose: Used for consistency in quality control results.
• Characteristics:
  • Known biochemical and susceptibility results for reliable quality control.
  • Nomenclature: Organisms are named using genus, species, and ATCC strain number (e.g., Staphylococcus aureus 29213™).
• Usage:
  • CLSI references specific ATCC strains for recommended quality control procedures.
  • Important to note the evolving nature of bacteria, as it affects susceptibility.

Subculturing Frozen/Stored Organisms

• General Note: Follow your laboratory's specific protocols for subculturing.
• Types of Organisms:
  • Commercial and patient-grown organisms stored using various methods.
  • Cultured organisms may be frozen on beads for long-term viability.
• Freezing Techniques:
  • Organisms preserved on beads (-70°C) to ensure indefinite use.
  • Beads are inoculated by mixing a large amount of organism, typically using a loop.
• Organizational Color Coding:
  • Colors of beads (e.g., red for Gram-negative, blue for Gram-positive) are for organization, not biological significance.

Subculturing Process

1. Main Culturing:
   • Beads can be directly placed on agar or reconstituted in saline before inoculating agar.
   • Initial culture is termed “F1”.
2. Additional Culturing:
   • Recommended to perform an additional subculture from F2 (termed “F3”).
   • Some laboratories may use F2 directly; however, over-subculturing can affect viability.
3. Media Types:
   • Commonly subcultured onto blood agar or nutrient-rich trypticase soy agar for fastidious organisms.
   • Specific agars, such as chocolate agar, may be necessary for certain organisms (e.g., H. influenzae, N. gonorrhoeae).

Control of Equipment

• Temperature Controls: Monitor daily within +/- 2°C for incubators, refrigerators, freezers, and lab humidity.
• Biological Safety Cabinets (BSC):
  • Airflow should be recorded daily; deep cleaning is essential.
  • Proper functioning is crucial for specimen handling, especially with highly pathogenic organisms.
• Incubator Control:
  • CO2 levels must be monitored daily; a known capnophilic organism (e.g., N. gonorrhoeae) can verify conditions by consistent growth.

Quality Control of Media

• Pre-made Media: Generally high-quality with consistent results, but still requires visual inspection upon receipt.
• QC Procedures:
  • Buffers must be used for testing media growth. For example, 0.5 McFarland reference can be utilized to ensure fastidious organisms grow properly on specific agars.

Control of Reagents and Antisera

• Testing: Daily or weekly testing of biochemical reagents, including positive and negative controls.
• Gram Stains: Quality control requires use of both Gram-positive and Gram-negative organisms.

Control of Antimicrobial Tests

• QC Frequency: Conduct weekly quality control using CLSI guidelines for both disk and automated methods.
• Mueller-Hinton Agar: Quality control upon receipt is necessary; however, diluted testing is minimal.

Control of Specimens

• Importance of Protocols: Proper specimen collection and handling are crucial for effective pathogen identification.
  • Examples of rejectable specimens include improperly labeled specimens or those that fail transport criteria.

Proficiency Testing

• Labs must adhere to quality standards set by external bodies like Accreditation Canada/IQMH.
  • Testing involves processing a 'fake' specimen that mimics standard procedures and evaluates reporting capabilities.

Learning Checks

1. Procedure for newly received Thayer-Martin media:
   • Set up QC first.
2. Handling improperly labeled CSF specimens:
   • Procedure for labeling must be followed accurately to avoid rejection.
3. Catalase reagent QC results indicate discrepancies:
   • Actions must involve repeating QC with appropriate standards.

References

• Link to ATCC resources and guidelines for microbiology best practices.