LQB362+Lecture+Week+3_25se1

Lecture Overview

  • Course: LQB362 Fundamentals of Microbiology

  • Instructor: Dr. Eva Hatje

  • Email: e.hatje@qut.edu.au

  • University Acknowledgment: Recognition of Turrbal and Yugara as traditional owners of the land.

Learning Resources

  • Textbooks:

    • Tortora, G. J., Funke, B. R., & Case, C. L. (2021). Microbiology: An Introduction (Thirteenth Edition).

      • Focus on Chapter 3 – Gram Staining.

    • Madigan, M. T., et al. (2022). Brock Biology of Microorganisms (Sixteenth Edition).

      • Focus on Chapter 29.

  • Acknowledgments: Thanks to A/Prof Francesca Frentiu for slide contributions.

Learning Outcomes

  1. Identify steps to isolate infectious agents from clinical specimens (collection and transport).

  2. Describe traditional microbial identification methods, including biochemical tests.

  3. Explain nucleic acid detection methods and the detection of microbial antigens and antibodies.

  4. Understand MALDI-TOF's role in diagnostic microbiology.

  5. Review timelines for microbiological testing from patient illness to diagnosis.

Laboratory Diagnosis of Infectious Diseases

  • Techniques:

    • Microscopy (e.g., Gram stain)

    • Culture

    • Serology testing

  • Specimen Types: Blood, urine, cerebrospinal fluid (CSF), sputum, etc.

Specimen Collection Considerations

  • Must collect identifiable information:

    • Patient’s Full Name

    • Date of Birth

    • Collection Date and Time

  • Types of specimens collected depend on the disease; aseptic techniques are crucial to prevent contamination.

Specimen Types

  • Blood

  • Urine

  • CSF

  • Faeces

  • Sputum

  • Wound swabs

  • Skin scrapings

  • Biopsies

  • Lung lavage

Sampling Considerations

  • Some body sites hold normal microbiota, affecting specimen quality (e.g. respiratory, gastrointestinal tracts).

  • Contamination Minimization: Use mid-stream urine collections or aseptic techniques.

  • Timing for Collection: Immediately before antimicrobial therapy.

Microbial Identification Methods

  • Conventional Techniques: Gram Staining, Isolation of Pure Colonies, Biochemical Tests.

  • Rapid Biochemical Tests: Catalase, Oxidase, Indole, Coagulase, Urease tests, etc.

Rapid Biochemical Tests

  • Catalase Test: Differentiates Streptococci (-) from Staphylococci (+).

  • Oxidase Test: Determines presence of cytochrome C oxidase, distinguishing Gram-negative species.

  • Indole Test: Distinguishes between Enterobacteriaceae (E. coli +, Klebsiella aerogenes -).

Nucleic Acid Detection Techniques

  • PCR: Amplifies DNA from the sample, useful for detecting pathogens without culture.

  • 16s rRNA Sequencing: For bacterial species identification based on ribosomal RNA differences.

  • qPCR: Quantitative PCR combines amplification and detection.

Serology Tests

  • Detect Antigens and Antibodies: Useful for diagnosing recent or past infections.

    • IgM: Indicates recent infection.

    • IgG: Indicates past infection or immunity.

Recent Technologies

  • MALDI-TOF: Analyzes chemical structures for microorganism identification.

    • Involves comparing mass profiles with established databases.

Summary of Diagnosis in Absence of Culture

  • Methods such as ELISA, PCR, and fluorescent antibody assays focus on rapid detection of microbial presence without traditional culturing.

Advantages and Disadvantages of Techniques

  • Microscopy: Fast, but poor sensitivity.

  • Culture: Definitive but time-consuming.

  • Serology: Good for non-culturable organisms but can have false results.

  • Molecular Detection: Fast and sensitive but requires specialized equipment.