Diagnosis of Bacterial Infections
Diagnosis of Bacterial Infections
Key Objectives:
Rapid submission of clinical specimens for isolation and identification.
Determine:
Infectious disease presence.
Specific pathogen causing the infection.
Antimicrobial sensitivity profile and antibiotic resistance.
Appropriate treatment plans.
Prevention measures and control plans.
Zoonotic potential and notification requirements.
Important Factors in Diagnosis
Considerations:
Animal species affected.
Clinical characteristics and disease state.
Epidemiology and the type of biospecimen.
Anatomical site of infection.
Methodology selection for sample collection and analysis.
Phases of Diagnosis
Phases:
Pre-analytical Phase:
Sample collection and preparation.
Analytical Phase:
Processing and analysis.
Post-analytical Phase:
Results review and reporting.
Interpretation and final diagnosis.
Specimen Collection and Key Steps
Choice of Specimen Collection:
Based on clinical symptoms, pathogen type, infection location, and duration.
Common Specimens:
Skin swabs, ear swabs, urine, wound swabs, blood, milk.
Importance:
Proper specimen collection is essential for accurate diagnostic testing.
Selection of Methodology
Detection Options:
Agent Detection:
Direct detection of bacteria.
Sample cultivation.
Taxonomic identification.
Host Immune Response:
Serology for detection of humoral immunity.
Detection of cell-mediated immunity.
Direct Detection of Bacteria
Methods:
Microscopy and differential staining.
Fluorescent antibody staining, including direct observation of stained or unstained preparations.
Importance:
Assess:
Bacterial density.
Morphology.
Host immune response.
Microorganism Observation Techniques
Common Staining Techniques:
Gram-staining.
Ziehl-Neelsen staining (acid-fast).
Fluorescent staining.
Example: Microscopy of milk samples indicating Gram-negative bacilli and immune response cells.
Sample Cultivation
Isolation Process:
Pathogens can be isolated using simple media (liquid or solid).
Importance of providing optimal nutrients, atmosphere, and temperature for bacterial growth.
Colony Formation:
One bacterium equals one Colony Forming Unit (CFU).
Culturing Fastidious Organisms
Techniques:
Use an anaerobic chamber for strict anaerobic bacteria cultivation.
Employ atmospheric jars with gas converters for altering atmospheric composition.
Media examples: Chocolate agar, chopped-meat broth.
Identification Techniques
Culturing:
Second culture techniques can yield pure pathogenic bacteria for identification.
Identification methods include biochemical characterization, proteomic techniques (MALDI-TOF), fatty-acid analysis (GC), and PCR.
Antigen Detection:
Use of monoclonal antibodies, serotyping, ELISA, and agglutination tests for pathogen detection.
Unculturable Bacteria
Definition:
Uncultivable bacteria refer to those that can't be grown on artificial media (~99%), while culturable bacteria are about 1%.
Host Immune Response Detection
Serology Methods:
Detect humoral immunity and response via antibody levels in serum.
Importance of seroconversion indicating recent exposure to pathogens.
Techniques for Serology Testing
Main Concepts:
Antibody titer measurement and its significance in diagnosing infections.
Seroconversion indicates development of antibodies post-exposure.
Tests:
IgM and IgG levels help assess exposure over time.
Cell-Mediated Immunity
Definition:
Response mechanisms involving immune cells rather than antibodies to clear intracellular pathogens (e.g., certain bacteria and viruses).
Tuberculin Skin Test
Principle:
Measures cell-mediated immunity; specifically used for infection by Mycobacterium bovis.
Procedure:
Conducted over 2 days; dermal response indicates prior exposure.
Interferon Gamma Test**
Overview:
A whole blood test for diagnosing Mycobacterium infections based on IFN-γ levels released from cells. Results available within 24 hours after sample collection.