Microbiology and Viral Infections

Microbiology

• Study of microorganisms, including bacteria, viruses, fungi, and protozoa
• Subfields:
  • Bacteriology: study of bacteria
  • Virology: study of viruses
  • Mycology: study of fungi
  • Parasitology: study of parasites

Viral Infections

• Viruses are not considered living organisms
• Cannot reproduce outside of host cells
• Types of viral infections:
  • Bacteriophage: infect bacteria
  • Archaeal viruses: infect archaea
  • Plant viruses: infect plants
  • Animal viruses: infect animals
• Viral replication:
  1. Attachment: virus attaches to host cell
  2. Penetration: virus enters host cell
  3. Uncoating: viral genome is released
  4. Transcription: viral genome is transcribed
  5. Translation: viral proteins are synthesized
  6. Assembly: new viral particles are assembled
  7. Release: new viral particles are released

Bacterial Classification

• Based on:
  • Morphology: shape and size
  • Metabolism: how they obtain energy
  • Biochemical tests: enzymatic reactions
  • Molecular analysis: DNA and RNA sequences
• Classification systems:
  • Bergey's Manual: most widely used system
  • Gram stain: distinguishes between Gram-positive and Gram-negative bacteria
• Taxonomic ranks:
  1. Domain
  2. Kingdom
  3. Phylum
  4. Class
  5. Order
  6. Family
  7. Genus
  8. Species

Disease

• Bacterial diseases:
  • Infectious diseases: caused by bacterial infection
  • Toxin-mediated diseases: caused by bacterial toxins
• Disease transmission:
  • Direct contact: direct contact with infected individual
  • Indirect contact: contact with contaminated surface or object
  • Vector-borne: transmitted through insects or animals
  • Airborne: transmitted through airborne particles
• Disease prevention:
  • Vaccination
  • Antibiotics
  • Personal protective equipment (PPE)
  • Improved sanitation and hygiene

Microbiology

• The study of microorganisms includes bacteria, viruses, fungi, and protozoa
• Subfields of microbiology include bacteriology, virology, mycology, and parasitology

Viral Infections

• Viruses are not considered living organisms because they cannot reproduce outside of host cells
• Viruses can infect bacteria (bacteriophage), archaea (archaeal viruses), plants (plant viruses), and animals (animal viruses)
• The stages of viral replication include attachment, penetration, uncoating, transcription, translation, assembly, and release
• These stages allow viruses to replicate and produce new viral particles within a host cell

Bacterial Classification

• Bacteria are classified based on morphology, metabolism, biochemical tests, and molecular analysis
• The Bergey's Manual is the most widely used classification system for bacteria
• The Gram stain is a classification system that distinguishes between Gram-positive and Gram-negative bacteria
• The taxonomic ranks for bacteria include domain, kingdom, phylum, class, order, family, genus, and species

Disease

• Bacterial diseases can be infectious diseases or toxin-mediated diseases
• Diseases can be transmitted through direct contact, indirect contact, vector-borne transmission, or airborne transmission
• Disease prevention methods include vaccination, antibiotics, personal protective equipment (PPE), and improved sanitation and hygiene

Bacterial Diseases

Types of Bacterial Diseases

• Infectious diseases occur when bacteria invade host tissues, causing diseases like tuberculosis and pneumonia
• Intoxications occur when bacterial toxins cause illness, such as in food poisoning and botulism
• Toxemias occur when bacterial toxins enter the bloodstream, causing diseases like sepsis

Mechanisms of Bacterial Pathogenesis

• Bacteria adhere to host cells, such as E.coli adhering to uroepithelial cells
• Bacteria invade host cells, such as Salmonella invading intestinal epithelial cells
• Bacteria produce toxins, such as Clostridium difficile producing enterotoxins
• Bacteria evade the host immune response, such as Staphylococcus aureus producing protein A to inhibit phagocytosis

Bacterial Diseases by System

• Respiratory system diseases include pneumonia, tuberculosis, and Legionnaires' disease
• Gastrointestinal system diseases include food poisoning, diarrhea, and cholera
• Skin and soft tissue diseases include impetigo, cellulitis, and abscesses
• Nervous system diseases include meningitis, encephalitis, and tetanus
• Urinary system diseases include urinary tract infections and pyelonephritis

Bacterial Virulence Factors

• Adhesins are proteins that facilitate bacterial attachment to host cells
• Capsules are polysaccharide layers that prevent phagocytosis
• Exotoxins are toxins released by bacteria, such as botulinum toxin
• Endotoxins are lipopolysaccharides present in Gram-negative bacterial cell walls

Epidemiology and Transmission

• Direct contact transmission occurs through person-to-person contact, such as with MRSA
• Indirect contact transmission occurs through contaminated surfaces, such as with Clostridium difficile
• Vector-borne transmission occurs through insects, such as with Lyme disease
• Food and waterborne transmission occurs through contaminated food and water, such as with Salmonella