Untitled Quiz

Agricultural Microbiology - MICR20010 Assessments

• Practical reports are due on time; avoid plagiarism (15%)
• Practical online MCQ exam on Friday, November 22nd, 2-3 pm (15%)
• Final MCQ exam in RDS on December 12th, 9:30 am (70%)

Remaining Lectures

• Lecture 10: Microorganisms and Disease
• Lecture 11: The Immune System
• Lecture 12: Pathogenic Bacteria
• Lecture 13: Pathogenic Fungi and Viruses
• Lecture 14: Antibiotic Resistant Microorganisms
• Lecture 15: Microbiology in the Food Industry (including fungi)
• Lecture 16: Microbiology in the Food Industry (fermentations)
• Lecture 17: The Nitrogen Cycle

Transmission of Disease

• Direct contact transmission: Examples demonstrating physical contact transmission
• Droplet transmission: The transmission of disease through aerosols produced by coughing, sneezing, or talking.
• Vehicle transmission: Diseases transmitted through an inanimate reservoir like food, water, or air.

Nosocomial Infections

• Acquired during a hospital stay
• Affects patients (number not specified)
• Transmission can be prevented by using gloves, masks, and face shields

Mechanisms of Pathogenicity

• Pathogenicity: The ability to cause disease
• Virulence: The extent of pathogenicity

Mechanisms of Pathogenicity (detailed)

• Portals of Entry:
  • Mucous membranes
  • Respiratory tract
  • Gastrointestinal tract
  • Genitourinary tract
  • Conjunctiva
  • Skin
  • Parenteral route
• Penetration or Evasion of Host Defenses:
  • Capsules
  • Cell wall components
  • Enzymes
  • Antigenic variation
  • Invasins
  • Intracellular growth
• Damage to Host Cells:
  • Siderophores
  • Direct damage
  • Toxins
  • Exotoxins
  • Endotoxins
  • Lysogenic conversion
  • Cytopathic effects
• Portals of Exit: The same mechanisms as the portals of entry

Infection and Adherence

• Adhesins/ligands bind to receptors on host cells:
  • Fimbriae (Escherichia coli)
  • M protein (Streptococcus)
• Formation of biofilms

Penetration into the Host Cell Cytoskeleton

• Invasins (proteins that facilitate entry):
  • Salmonella, altering host actin to enter a host cell
  • Listeria, using actin to move between cells

Direct Damage by Bacteria

• Disrupt host cell function
• Produce waste products
• Toxins
  • Toxin: Substance contributing to pathogenicity
  • Toxigenicity: The ability to produce a toxin
  • Toxemia: Presence of toxin in the host's blood

Exotoxins (types)

• A table with examples of bacteria and their corresponding exotoxins
  • Corynebacterium diphtheriae: A-B toxin
  • Streptococcus pyogenes: membrane-disrupting; erythrogenic toxin
  • Clostridium botulinum: A-B toxin; neurotoxin
  • C. tetani: A-B toxin; neurotoxin
  • Vibrio cholerae: A-B toxin; enterotoxin
  • Staphylococcus aureus: Superantigen

Endotoxins

• Source: Gram-negative outer membrane
• Chemistry: Lipid A
• Fever? Yes
• Neutralized by Antitoxin? No
• LD50: Relatively large

The Stages of a Disease

• A graph illustrating the stages of a disease
  • Incubation period (no signs or symptoms)
  • Prodromal period (mild symptoms)
  • Period of illness (severe symptoms)
  • Period of decline (symptoms lessen)
  • Period of convalescence (recovery)

Bacterial Diseases (Chronic vs Acute)

• Information about various bacterial diseases and their classification as chronic or acute

Pseudomonas and the Pseudomonads

• Colony Morphology: Rod-shaped or curved rods with polar flagellae
• Burkholderia, Pseudomonas, etc.
• Challenge for patients with Cystic Fibrosis

The Human Lung

• Diagram of the human lung, showing the various sections from the nasal passage through to the alveoli and relevant detail

Developing Chronic Infection

• Intermittent colonization first
• Followed by a persistent chronic infection
• Accompanied by a higher degree of inflammation

B. Pertussis - An Acute Infection

• Gram-negative rod-shaped bacterium
• Lung infection, but not opportunistic
• Highly contagious due to coughing spasms
• Uses virulence factors to cause disease

Whooping Cough (Symptoms and Treatment)

• Symptoms:
  • Paroxysmal cough (“whoop”)
  • Rib fractures, hernias, loss of consciousness
• Severity for newborns: High risk of death
• Incubation and catarrhal stages, followed by uncontrollable fits
• Prevention/Treatment: Vaccination with pertussis toxin, is relatively successful. Vaccination uptake is critical

H. pylori - Commensal or Pathogen?

• Gram-negative spiral organism
• Resides in the human stomach/duodenum
• Often asymptomatic, but can cause gastritis in most individuals
  • More serious diseases: Duodenal Ulcers, MALT Lymphoma, Gastric Cancer
• Brief History: Discovered in 1982, it was initially thought stomach was sterile, and ulcers were due to stress.
• Pathology of Infection:
  • Can colonize the human gastric mucosa
  • Causes gastritis (in most individuals colonized), which can be asymptomatic
  • Can develop into more serious diseases like duodenal ulcers and gastric cancers (A class 1 carcinogen?)
• Disease Progression: A schematic visualizes the progression of disease: Normal, Acute, Chronic; various types of gastritis, Intestinal metaplasia, and Gastric cancer stages.

Chlamydia – An Intracellular Pathogen

• 15-25 year olds are at the highest risk..
• Cases are rising steadily
• Obligate intracellular parasite (needs host cell for survival)
  • C. trachomatis (STD and trachoma)
  • C. psittaci (Psittacosis)
  • C. pneumoniae (Respiratory syndromes)
• Limited metabolic pathways
• Lack some genes (ftsZ)
• Presence of eukaryotic-like genes
• Life Cycle: Elementary and Reticulate bodies

Bacterial Diseases of the Eye

• Chlamydia trachomatis causes trachoma
• Leading cause of blindness worldwide
• Scars from infection abrade the cornea and cause blindness

Anthrax

• Bacillus anthracis, with endospores
• Endospores enter through minor wounds, 20% mortality
• Gastrointestinal Anthrax. Ingestion of undercooked or contaminated food, 50% fatality
• Inhalational Anthrax. Inhaling endospores, 100% mortality

Biological Weapons

• Historical examples of biological weapons use (plagues, flea bombs)

Biological Weapons (Bacteria and Viruses)

• Table listing types of bacteria and viruses that have been used in biological weapons

Typhoid Fever

• Salmonella typhi causing typhoid fever
• Bacteria spreads throughout body in phagocytes
• 1-3% of those recovered become chronic carriers
• 200,000 fatalities
• Important aspect of asymptomatic infection

Pathogenic Fungi and Viruses (Next Topic)

• Next topic in the course