Study Notes for General Microbiology Exam II

Instructor Information

  • Name: Cangliang Shen

  • Degree: Ph. D.

  • Institution: School of Agriculture and Food System Division of Land Grant Engagement, West Virginia University

  • Email: cangliang.shen@mail.wvu.edu

General Microbiology Exam 2 - Lecture Notes Overview

Lecture 1: Human Disease Caused by Bacteria (1)

Respiratory System Anatomy

  • Upper Respiratory Tract Components:

    • Nasolacrimal duct

    • Nasal sinus

    • Tongue

    • Tonsils

    • Nasopharynx

    • Auditory canal

    • Oropharynx

    • Epiglottis

    • Glottis

  • Lower Respiratory Tract Components:

    • Trachea

    • Bronchi

    • Bronchioles

    • Alveoli (greatly enlarged)

Diseases Transmitted Through the Respiratory Tract

  • Table of Diseases and Organisms:

    • Diphtheria

    • Organism: Corynebacterium diphtheriae

    • Whooping Cough

    • Organism: Bordetella pertussis

    • Pneumonia

    • Organisms:

      • Streptococcus pneumoniae

      • Mycoplasma pneumoniae

      • Klebsiella pneumoniae

      • Streptococcus pyogenes

      • Haemophilus influenzae

      • Neisseria meningitidis

      • Mycobacterium tuberculosis

Diphtheria

  • Causes:

    • Caused by Corynebacterium diphtheriae, a Gram-positive bacterium.

    • Lysogenized strains produce an exotoxin inhibiting protein synthesis and contributing to pathogenesis.

  • Transmission:

    • Airborne via nasopharyngeal secretions; increased transmission likelihood in crowded settings.

  • Diagnosis:

    • Observation of pseudomembrane in the throat, bacterial culture.

  • Treatment and Prevention:

    • Antitoxin for neutralizing unabsorbed exotoxin.

    • Antibiotic therapy.

    • Vaccination with DPT or acellular DTaP vaccine.

Mechanism of Action of Diphtheria Toxin

  • Toxin Structure:

    • Toxin formed with A chain and B chain linked by a disulfide bond.

  • Action Steps:

    1. B chain binds to the receptor on susceptible cells.

    2. Endocytosis occurs, leading to the release of the active enzyme from the endosome.

    3. The enzyme inhibits protein synthesis, resulting in cell death.

    • Overall Mechanism:

    • NAD+ and EF-2 are modified causing inhibition of protein synthesis.

Meningitis

  • Definition:

    • Inflammation of the brain or spinal cord meninges.

  • Bacterial Causes:

    • Major pathogens include Streptococcus pneumoniae, Neisseria meningitidis, and Haemophilus influenzae.

  • Transmission:

    • Primarily through respiratory droplets.

  • Clinical Manifestations:

    • Initial respiratory illness/sore throat followed by symptoms: vomiting, headache, lethargy, confusion, and neck stiffness.

  • Diagnosis:

    • Gram stain and culture of cerebrospinal fluid (CSF).

  • Prevention and Control:

    • Antibiotic therapy and vaccination.

Whooping Cough (Pertussis)

  • Cause:

    • Bordetella pertussis, a Gram-negative bacterium.

  • Transmission:

    • Very contagious; transmitted via droplet inhalation.

  • Toxins Produced:

    • Pertussis toxin (stops protein synthesis), tracheal cytotoxin, and dermonecrotic toxin (destroy epithelial tissue).

Clinical Features of Pertussis

  • Stages of Disease:

    • Initial cold-like symptoms; progresses to severe coughing spells with a characteristic whoop.

  • Immune Response:

    • Permanent or long-lasting immunity develops post-infection.

  • Diagnosis:

    • Bacterial culture, fluorescent antibody staining, serological tests.

  • Treatment and Prevention:

    • Antibiotics and vaccination with DPT or Tdap for older groups.

Streptococcal Pneumonia

  • Causative Agent:

    • Streptococcus pneumoniae, an opportunistic pathogen.

  • Disease Characteristics:

    • Produces polysaccharide capsule and toxins, causing lobar pneumonia.

  • Clinical Presentation:

    • Fever, chest pain, cough; respiratory distress with rust-colored sputum.

  • Diagnosis and Treatment:

    • Chest X-ray, gram stain and culture.

    • Antibiotic therapy and vaccination (Pneumovax).

Lecture 2: Human Disease Caused by Bacteria (2)

Digestive Tract Overview

  • Components of the Human Digestive Tract:

    • Oral cavity, esophagus, liver, stomach, pancreas, large intestine, rectum, anus, salivary glands, gallbladder, small intestine, appendix.

  • Normal Flora of Alimentary Tract:

    • Stomach: 10^2 cells/ml

    • Small Intestine: 10^4 cells/ml

    • Large Intestine: 10^12 cells/g (anaerobic to aerobic ratio of 1000:1)

  • Fecal Composition: Approximately one-third bacterial cells.

Gastrointestinal Diseases Caused by Food Poisoning Bacteria

  • Common Bacterial Agents:

    • Staphylococcus aureus: 1-6 hours onset, symptoms include nausea, vomiting, diarrhea.

    • Clostridium botulinum: 18-36 hours onset, dizziness, double vision, respiratory issues.

    • Bacillus cereus: Symptoms can occur within 1-6 hours (vomiting) or 10-12 hours (abdominal pain, diarrhea.)

  • Mechanism of Action:

    • Toxins produced in food that can cause illness once ingested.

Tetanus

  • Clinical Manifestations:

    • Early signs include muscle cramping and tension; advanced disease manifests as trismus and board-like rigidity.

  • Cause of Death:

    • Asphyxiation due to spasms of diaphragm and intercostal respiratory muscles.

  • Diagnosis and Treatment:

    • Diagnosis based on clinical history; treatment involves antibiotics and antitoxin.

    • Active immunization via DPT vaccine recommended.

Botulism and Tetanus Toxins

  • Comparison of Actions:

    • Botulism toxin inhibits acetylcholine release, preventing muscle contraction.

    • Tetanus toxin inhibits glycine release, preventing muscle relaxation.

Gas Gangrene

  • Causative Agent:

    • Clostridium perfringens, characterized as a Gram-positive, spore-forming rod.

  • Pathogenic Mechanism:

    • Contamination leads to necrotizing infection due to toxin secretion and tissue degradation enzymes.

Clostridium Difficile Infection (CDI)

  • Pathophysiology:

    • Overgrowth follows antibiotic treatment, resulting in colitis.

  • Symptoms: Diarrhea, pseudomembranous colitis, and potentially toxic megacolon.

  • Treatment: Requires detection of Gram-positive, beta-hemolytic bacteria in culture, antibiotics following the identification of relevant species.

Other Gastrointestinal Infections

  • Common Infectious Agents and Diseases:

    • Salmonella typhimurium -> salmonellosis

    • Vibrio cholera -> cholera due to fecal contamination of water.

  • Rabies Management:

    • Prophylactic measures taken after exposure to infectious wildlife or humans.

Oral Health and Streptococcus mutans

  • Pathogenic Mechanism:

    • Secretion of sticky dextran, facilitating plaque formation through anaerobic fermentation of sucrose.

  • Consequences:

    • Leads to lactic acid accumulation, demineralization of tooth enamel.

Miscellaneous Microbiology Topics and Mechanisms of Disease

Sexually Transmitted Diseases (STDs)

  • Public Health Challenge:

    • Approximately 300 million new cases annually, affecting mainly those aged 15–30.

  • Gonorrhea:

    • Caused by Neisseria gonorrhoeae, symptoms include urethral discharge and pain.

    • Diagnosis through culture and sensitivity testing, treatment with antibiotics.

  • Syphilis:

    • Caused by Treponema pallidum, involves three distinguishable stages affecting various body systems.

    • Public health measures include comprehensive sex education and contact tracing for effective management.

Lyme Disease

  • Pathogenesis and Transmission:

    • Borrelia burgdorferi transmitted via tick bites; presents with characteristic bull's eye rash.

  • Diagnosis and Treatment:

    • Serological testing is essential for confirmation, treated effectively with early antibiotic therapy.

Antimicrobial Therapy Overview

  • Definitions:

    • Antibiotics: Substances produced by microorganisms that inhibit or kill other microbes.

    • Chemotherapeutic Agents: Synthetic or naturally derived substances administered for disease treatment.

  • Key Historical Developments:

    • Discovery of penicillin (1929), streptomycin (1944), and broad-spectrum antibiotics change the landscape of microbial disease management.

Antimicrobial Drug Characteristics

  • Selectivity and Spectrum:

    • Selective toxicity aimed at pathogens with minimal effect on the host.

    • Narrow vs. broad-spectrum classifications based on the range of pathogens targeted.

Mechanisms of Action in Antimicrobial Drugs

  • Inhibition Areas:

    • Cell wall synthesis (e.g., β-lactams), protein synthesis (e.g., aminoglycosides), nucleic acid synthesis, and metabolic pathways.

  • Drug Testing Methods:

    • Kirby-Bauer disk diffusion method and E test for determining minimum inhibitory concentration (MIC).

Microbial Control Methods

  • Microbial Death and Control:

    • Antimicrobial agents must exceed certain concentrations to effectively inhibit or kill bacteria.

    • Importance of understanding factors influencing microbial resistance, such as population size, concentration of agents, and environmental conditions.

  • Physical vs. Chemical Control:

    • Useful methods include dry/moist heat sterilization, radiation, and chemical agents (alcohols, oxidizing agents).

Summary Points
Antimicrobial Regulations and Efficacy

  • Regulatory Oversight:

    • Sanitizer registration requires efficacy data, chemistry, and toxicology data, ensuring safety in food contact surfaces.

    • Use of registered agents like chlorine-based sanitizers and quaternary ammonium compounds for effective control.

Conclusion

  • Gaining an understanding of these pathogens and methods provides essential knowledge in public health and disease prevention strategies.