Mycotoxins Overview Quiz

Mycotoxins

• Mycotoxins are produced by certain types of mold.
• Mycotoxins can contaminate food and animal feeds, posing risks to humans and livestock.
• Aflatoxins, ochratoxin A, patulin, fumonisins, zearalenone and deoxynivalenol (DON) are among the most common mycotoxins.
• Mycotoxins cause various health problems in humans and animals, including gastroenteritis, immunosuppression, neurotoxicity, teratogenicity, nephrotoxicity, hepatotoxicity, mutagenicity, and carcinogenicity.
• Mycotoxins cause significant economic losses, particularly in developing countries.
• Fungal growth and toxin production can occur during both growing and storage conditions.
• Field fungi: Alternaria, Cladosporium, Fusarium spp.
• Storage fungi: Aspergillus, Penicillium and Fusarium spp.
• Molds are aerobic and can grow at low water activity (0.65), refrigerated temperatures, and low pH (pH 3.5).
• Optimal conditions for mold growth: 25-30 °C temperature, 13-18% moisture level
• Vacuum packaging and thermal processes can inhibit growth.
• Most mycotoxin-producing mold strains belong to the genera Aspergillus, Fusarium, and Penicillium.

Norovirus

• Family: Caliciviridae, naked, ss RNA, 38 nm diameter
• Cause of acute gastroenteritis in the USA and Europe (Winter vomiting disease)
• Infective dose: 10-100 viral particles; incubation period: 24-48 hours
• Symptoms: acute-onset vomiting, watery diarrhea with abdominal cramps, and nausea.
• Virus shedding in stool begins with symptom onset and lasts up to 24-72 hours after exposure.
• Transmission: contaminated food or water; direct person-to-person spread.
• Oysters and shellfish are common sources.
• Norovirus is resistant to chlorine.
• Vaccine development is challenging.

Polio Virus

• Family: Picornaviridae, single-stranded RNA viruses.
• Transmission: fecal-oral route (food, water); person-to-person spread.
• Causes gastrointestinal illness and poliomyelitis (polio).
• Initial symptoms: fever, fatigue, headache, vomiting, stiffness in the neck, and pain in the limbs.
• Second stage: the virus invades the meninges causing back pain and headaches.
• In severe cases, the virus can spread to the spinal cord causing paralysis (lower limbs).
• The virus is shed intermittently in feces for several weeks.
• Vaccination: likely to be fully eradicated in the near future.

Hepatitis A Virus

• ssRNA
• Replicates in the gut and liver, shed in feces.
• Transmission:
  • Person to person
  • Contaminated drinking water and food (vegetables, seafood, shellfish).
• Causes infectious hepatitis.
• Symptoms: anorexia, vomiting, malaise, fever, dark urine, and jaundice.
• Symptoms are more severe in older adults than children.
• Childhood infection results in lifetime immunity.
• The virus is resistant to low pH, and relatively resistant to free chlorine.
• Destruction: heating to over 85 °C for 1 minute; disinfecting surfaces with 1:100 solution of sodium hypochlorite.

Hepatitis E

• Calici-like particle, ss RNA
• Spread through drinking water.
• Incubation time: 15-60 days.
• Illness resembles hepatitis A.
• No chronic carriers, no vaccine available.

Prevention Methods for Foodborne Viruses

• Proper heat treatment of food: pasteurization effectively kills viruses.
• Disinfecting surfaces, equipment, and water with hypochlorite.
• Good personal hygiene.
• Keep suspected individuals away from handling food.
• Vaccination.

Microscopy and Staining

• Microscopes use lenses to magnify images of cells.
• Light microscopes: use visible light to illuminate cell structures.
• Compound microscopes: use multiple magnifying lenses.
• Limit of resolution (light microscope): ~0.2 µm.
  • Types of compound light microscopes:
    • Bright-field
    • Phase-contrast
    • Dark-field
    • Fluorescence
• Electron microscopes: use electron beams for higher magnification and resolution.
  • Magnification: 100,000X
  • Resolution: 0.2 nm
  • Types of electron microscopes:
    • Transmission Electron microscope (TEM)

Bright-Field Compound Microscope

• Most commonly used microscope in the laboratory.
• Uses two sets of lenses: objective and ocular.
• Total magnification: objective magnification x ocular magnification.
• Maximum magnification: ~1000X (1500X).
• Resolution: The ability to distinguish fine details and structures.
• Determined by:
  • Wavelength of the light source
  • Numerical aperture of the lens (NA).
• Limit of resolution (light microscope): ~0.2 µm.

Bacterial Staining

• Used to color cells and improve contrast in light microscopy.
• Basic dyes bind to negatively charged components of cells, like cell wall structures.
  • Examples of dyes: Methylene blue, Safranin, Crystal violet.

Staining Techniques in Bacteria

• Simple stain: one type of stain is used.
• Differential staining: two dyes are used.
• Gram stain: Distinguishes bacteria with different cell wall structures.
  • Uses crystal violet (primary dye) and safranin (secondary dye).

Gram Stain

• Classifies bacteria as Gram-positive or Gram-negative based on cell wall structure response to staining.
• Gram-positive bacteria:
  • Retain the crystal violet-iodine complex after alcohol wash.
  • Appear purple under the microscope.
• Gram-negative bacteria:
  • Do not retain the dye-iodine complex, become translucent.
  • Counter stained with safranin, appear red under the microscope.

Bacterial Cell Structure

• Prokaryotic cells lack complex internal organelles.
• Gram-positive and Gram-negative bacteria differ in cell wall structure.

Bacterial Cell Wall

• Thick, rigid structure external to the cell membrane.
• Maintains cell integrity (shape, rigidity, protection).
• Fully permeable.
• Composed of peptidoglycan, a polymer of:
  • N-acetylmuramic acid
  • N-acetylglucosamine
• Cross-linked by polypeptides.

Gram-Positive and Gram-Negative Bacteria

• Gram-positive bacteria:
  • Thick layer of peptidoglycan (90%).
  • Embedded teichoic acids.
• Gram-negative bacteria:
  • Thin layer of peptidoglycan (10%).
  • Additional outer membrane.
  • Outer membrane: contains lipopolysaccharides (LPS) chains (antigen O).
  • LPS (lipopolysaccharide): endotoxin of Gram-negative bacteria, a virulence factor.

Structures External to the Cell Wall

• Not all bacteria have all of these structures.
• Capsule and slime layer (Glycocalyx):
  • Capsule: a dense, well-defined structure that adheres tightly to the cell wall.
  • Slime layer: a diffuse, unorganized layer that loosely surrounds the cell.
• Flagella:
  • Long, hair-like appendages made of protein (20 nm diameter, 20 mm long).
  • Used for locomotion in many bacteria.
  • Different patterns of flagella.
• Pili and fimbriae:
  • Short filaments made of protein.
  • Fimbriae: used for attachment.
  • Sex pili: longer than fimbriae, assist in conjugation.