Lec 6 Microbio on 25 February 2025 at 20.11.55 PM

Spores and Psychotropic Bacteria

  • Listeria and Corynebacterium

    • Listeria is psychotropic, meaning it can grow at lower temperatures, making it a concern in foodborne illnesses; it crosses three protective barriers in the body.

    • Corynebacterium requires infection by a bacteriophage for exotoxin production; the bacteriophage encodes the toxin.

Gram-Negative Bacilli

  • Discussed the gram-negative non-spore forming bacilli.

    • Most gram-negative bacilli discussed are enteric, causing issues in the intestinal tract.

    • Nonenteric gram-negative bacilli cause issues outside the intestinal tract, such as Cronobacter, which affects low birth weight babies and is linked to powdered infant formula.

Agar and Bacterial Classification

  • Focus on McConkey Agar

    • Key differences between selective and differential agars should be understood. McConkey agar aids in differentiating gram-negative bacteria based on lactose fermentation.

Enteric Classification

  • Classification of enterics based on antigen structures:

    • O, K, and H antigens:

      • O antigen: part of the outer membrane

      • K antigen: capsular antigen

      • H antigen: flagellar antigen

    • Identification can also be done biochemically through various biochemical tests.

Mycobacteria

  • Mycobacterium species discussed:

    • One species causes tuberculosis and another causes leprosy.

    • Mycobacteria have a complex cell wall rich in mycolic acids, making them not easily stained by traditional Gram stain methods; they are classified as acid-fast bacilli.

    • Use of Ziehl-Neelsen staining technique is necessary for visualizing mycobacteria.

Tuberculosis (TB) Basics

  • TB develops after inhalation of mycobacterium (aerosol transmission), with a slow progression. Infections can remain dormant or can develop to cause diseases in organs beyond the lungs (kidneys, bones).

    • Primary TB complex forms when white blood cells ingest bacteria. Most cases remain asymptomatic after this stage.

    • Postprimary TB occurs when bacteria escape the primary complex and cause tissue damage, leading to symptoms and further infections.

Tuberculosis Testing

  • The TB test entails injecting tuberculin (a protein derived from mycobacterium) intradermally.

    • The test looks for induration (hardened bump) rather than redness to determine positive results.

    • A positive test does not necessarily confirm active infection; it indicates prior exposure to TB.

    • Following a positive test, further assessments like chest X-rays may be conducted.

Mycobacterium Leprae

  • Causes leprosy, presenting mainly in two forms:

    • Lepromatous Leprosy: Highly infective and disfiguring.

    • Tuberculoid Leprosy: Less severe with visible nerve enlargement and fewer lesions.

Other Pathogens and Considerations

  • Notable pathogens include:

    • Spirochetes: Treponema pallidum causes syphilis while Borrelia burgdorferi leads to Lyme disease.

      • Syphilis is diagnosed using nontreponemal tests based on cardiolipin clumping reactions and confirmed with specific treponemal tests.

    • Chlamydia: Chlamydia trachomatis and chlamydia cetaceae are key for STDs and other diseases. Chlamydia can cause trachoma and other complications during childbirth; screening is vital.

      • Transmission occurs via direct contact (elementary body form) which then converts to reticulate body within hosts.

    • Mycoplasma pneumoniae causes walking pneumonia; it lacks a cell wall and cannot be gram-stained.

Fungal Infections

  • Focus on two significant fungal pathogens:

    • Cryptococcus neoformans: Invasive fungal infection mainly affecting immunocompromised individuals.

    • Aspergillus flavus: Produces aflatoxin, which poses agricultural risks due to contamination of crops.

    • Fungi spread through inhalation rather than person-to-person contact; surface infections can progress to systemic infections.

Review of Pathogen Characteristics

  • Key pathogen identification features include whether they are gram-stainable, their modes of transmission, their clinical presentations, and necessary treatment or prevention measures.

  • Stress on understanding the transmission pathways and preventative measures for infections, such as vector control for Lyme disease (ticks) and safe practices to avoid STDs (chlamydia).

Conclusion

  • Significant focus laid upon understanding unique bacterial characteristics, modes of transmission, clinical manifestations, diagnostics, and the importance of timely treatment and preventive measures for various infectious diseases.