Microbial Diversity and Classification

Normal Microbiota vs. Pathogens

• Definition of Normal Microbiota (Normal Flora): Refers to the bacteria that are expected to inhabit our bodies and contribute to our health.

  • The term "flora" historically referred to plant life, but is used here to describe these bacteria.

  • Most normal flora is beneficial and plays a role in health protection.

• Benefits of Normal Microbiota:

  • Prevent diseases by outcompeting pathogens for resources (space, nutrients).

  • Produce antibiotics to suppress harmful bacteria.

• Pathogens:

  • Defined as microbes capable of causing disease in a healthy host.

Microbial Diversity

• Biodiversity of Microbes:

  • The number of bacterial species significantly exceeds that of mammals by over 10,000.

  • Less than 1% of bacterial species have been studied due to various inspection difficulties (e.g., laboratory growth constraints).

• Domains of Life:

  • Bacteria: Prokaryotic cells without nuclei or organelles; their DNA is stored in a nucleoid region.

  • Archaea: Also prokaryotic but distinct from bacteria; lack peptidoglycan, possess unique RNA types, and often are extremophiles.

  • Archaea can thrive in extreme environments (high salinity, temperature, anaerobic conditions).

  • Eukarya: Organisms with true nuclei and organelles, including protozoa, fungi, algae.

Key Bacterial Structures and Characteristics

• Prokaryotes:

  • No nucleus indicates that they existed before eukaryotic cells.

• Nucleoid:

  • The region where bacterial DNA is located; lacks a membrane.

• Peptidoglycan:

  • A unique component of bacterial cell walls critical for maintaining structural integrity.

Eukaryotes and Microbial Organisms

• Eukaryotic Microbes:

  • This group includes potential pathogens (e.g., protozoans) and beneficial organisms (e.g., algae).

  • Fungi:

  • Emphasis on yeast rather than mushrooms or molds due to their relevance in human diseases.

  • Discuss inhalation of spores and associated diseases.

• Protozoa:

  • Animal-like organisms relevant to human health; for example, the malaria-causing protozoan.

Naming Microorganisms: Binomial Nomenclature

• Scientific Naming: Utilizes a two-name system: Genus + Species.

  • Example:

  • Escherichia coli:

    • Genus: Escherichia (capitalized)

    • Species: coli (lowercase, italicized or underlined).

Nonliving Microbial Agents

• Viruses:

  • Composed of nucleic acids in protein; these obligate intracellular parasites are inactive outside a host cell.

• Viroids:

  • Simple RNA fragments that can cause diseases mainly in plants; less evidence for human diseases.

• Prions:

  • Infectious proteins with no nucleic acid; misfolded forms of normal proteins.

  • Associated with diseases like BSE and Creutzfeldt-Jakob disease.

Size Comparison of Microbes

• Size Order:

  • Eukaryotic cells > Bacteria > Viruses

  • In general, eukaryotic cells are 10-100x larger than bacteria, which are 10-100x larger than most viruses.

  • Size varies (e.g., smallest bacteria can be similar to larger viruses).

Conclusion

• Overview of topics covered includes diversity of life forms, naming conventions, and differences between living and nonliving microbes.

• Next topic will delve into microscopy techniques.