Microbiology Essentials Quiz

Microorganisms

• Microorganisms are crucial for life on Earth, participating in carbon and nitrogen cycles
• Decomposition of dead organic matter depends on microorganisms
• Soil fertility is affected by microorganisms
• Probiotic bacteria compete with pathogens for nutrients and attachment sites, thus preventing harmful infections
• "Friendly" bacteria protect by producing antimicrobial chemicals

Types of Infectious Agents

• Infectious diseases can be caused by agents that aren't living microorganisms:
  • Prions are abnormal proteins causing disease
  • Viruses consist of nucleic acid and protein, but lack cellular structure
  • Bacteria are the simplest living cells, easily grown in labs
  • Fungi and protozoa are more complex than bacteria, many have sexual reproduction
    • Most fungi act as contaminants or spoilage organisms
    • Protozoa are primarily pathogens

Viruses and Prions

• Viruses infect all types of organisms (animals, plants, protozoa, bacteria)

• Viruses vary in size and structure, but all contain nucleic acid and protein (the protein protects the nucleic acid)

• Nucleic acid can be single-stranded or double-stranded DNA or RNA

• Virus sizes range in diameter from approximately 20nm (common cold virus) to 300nm (chicken pox virus); some elongated viruses (like Ebola) are much longer but very narrow

• Viruses require a host cell for replication and growth

• Viruses can only grow inside a host cell, and the host range is usually limited to a single species (although rabies is an exception)

• Viruses can be present in pharmaceutical raw materials of animal origin

• Viruses are relatively susceptible to heat and organic solvents, so unlikely to survive in materials like gelatin

• Viruses primarily act as pathogens

Bacteria

• Bacteria are responsible for a wide range of diseases

• Bacteria were discovered centuries before viruses

• Most bacteria are easy to grow in labs, making them a widely studied group

• Bacteria are typically spherical or rod-shaped cells (measuring 1-10 mm) and can be seen with a light microscope once stained

• Bacteria are very robust compared to human cells; the cell wall protects against osmotic pressure changes

• Bacteria can easily survive transfer to water from infection sites

• Bacteria tolerate a wide range of temperatures and pH, as well as exposure to UV light, ionizing radiation, and toxic chemicals

• bacteria reproduce asexually and have a rapid reproduction rate

• Bacterial reproduction by binary fission allows a single cell to produce over 16 million cells in about 8 hours

• A large number of bacteria may be visible to the naked eye as a colony

• Mutations play a critical role in bacterial genetic variation because of asexual reproduction

• While bacteria grow more slowly in the human body than on Petri dishes due to immune system attack and competition for resources, antibiotic-resistant mutants can still evolve during antibiotic treatment

• Cell wall is both a benefit (osmotic pressure & drying protection) and a disadvantage (target for antibiotics like penicillin)

• Ribosomes, also structurally different from eukaryotic cells, are another target for antibiotics

• Shape, size and complexity variations created classification problems in the past

• Some pathogenic bacteria are intracellular parasites like Chlamydia and Rickettsia, growing within host cells with much of the biology resembling that of viruses

• Mycoplasmas are a subgroup of bacteria lacking a cell wall, making them resistant to penicillin and related antibiotics

Prions

• Prions are the simplest infectious agents, non-living but treated like microorganisms due to their ability to transmit disease between individuals
• Prions are unusual proteins that interact with normal proteins to cause structural changes
• Prions lead to fatal nerve-degenerative diseases called transmissible spongiform encephalopathies
• BSE ("mad cow disease") and Creutzfeldt-Jakob disease (CJD) are examples of diseases caused by prions
• Prions are very stable and hard to inactivate