KN

Lecture 20

Exam Overview

  • Exam 4 format similar to Exam 3
  • Strategy: Answer short answer questions first
  • Open office hours on Zoom (Apr 8, 7-8 pm)
  • Email notifications for homework and team activities
  • Extra credit for 75% completion on TRACE

Topics Covered Today

  • Pathogen Identification
    • Biochemical Profiles
    • Nucleic Acid Amplification Tests (NAATs, e.g., PCR)
    • Point-of-Care Rapid Diagnostics Tests
  • Review for Exam 4

Case Study: Thomas's Illness

  • Background: Thomas (5 years old) and family visit a fair
  • Symptoms: Stomach cramps, vomiting, diarrhea, blood in diarrhea
  • Treatment Journey: Initial doctor's appointment leads to diagnosis of acute renal failure
  • Sample Collection: Urine, blood, and stool samples collected for testing

Pathogen Identification Techniques

1. Biochemical Profiles

  • Definition: Used primarily for bacteria to identify microbial pathogens
  • Methods: Employ selective and differential media, dichotomous keys
  • Key Bacterial Examples:
    • Streptococcus pneumoniae: Identified via optochin sensitivity
    • Staphylococcus aureus: Has positive coagulase test | Catalase positive

2. PCR (Polymerase Chain Reaction)

  • Function: Amplifies DNA from pathogens (no need for viable cells)
    • Allows detection of specific sequences from pathogens (viral & hard-to-culture bacteria)
    • Provides visual results through gel electrophoresis
  • Procedure Overview:
    • Primers bind to specific pathogen genes
    • RNA extracted from samples, converted to DNA
    • Amplification with specific primers followed by result interpretation

3. Advantages and Disadvantages of Identification Techniques

  • Biochemical Tests:
    • Advantages: Provide pure cultures, useful for antibiotic susceptibility testing
    • Disadvantages: Time-consuming, not effective on hard-to-culture organisms, infection risk to staff
  • PCR - NAATs:
    • Advantages: High sensitivity, rapid results, effective for hard-to-culture pathogens
    • Disadvantages: High cost, complex technology, limited information on pathogen susceptibility

Point-of-Care Rapid Diagnostics

  • Focus: Fast diagnosis of infectious diseases
  • Sensitivity vs. Specificity:
    • Sensitivity: Correctly identifies those with the disease (true positives)
    • Specificity: Correctly identifies those without the disease (true negatives)
  • Immunochromatography (example: pregnancy tests)
  • Advantages: Fast results, no culturing, helps prevent unnecessary antibiotic use
  • Disadvantages: Risk of missing multiple infections, no data on antibiotic sensitivity

Important Metrics:

  • Sensitivity & Specificity in Diagnostic Tests
  • Understanding percentage values and how they affect test credibility

Summary of Case Study Tests

  • Testing Focus on E. coli 0157:H7:
    • Toxin Production: Produces Shiga toxin impacting kidneys
    • PCR analysis confirms presence of toxin gene, indicating pathogenic strain

Review Points for Exam 4

  • Review all identification techniques, case studies, and diagnostic tests
  • Understand key microbial characteristics and their implications for diagnosis and treatment
  • Prepare for questions about symptoms, pathogen tests, and immunological responses.