10 Questions
What is the term used to describe the collective group of microorganisms including bacteria, archaea, viruses, fungi, prions, protozoa, and algae?
Microbes
Which of the following microorganisms lacks nucleic acid and consists only of infectious proteinaceous particles?
Prions
What is the characteristic that distinguishes viruses from cellular microorganisms?
Dependence on host cells for synthesis of macromolecules
What is the major difference between prions and other microorganisms?
Lack of nucleic acid
Who are the pioneers in the field of medical microbiology?
Pasteur and Koch
What is the primary characteristic that distinguishes prokaryotes from eukaryotes?
Absence of nucleus
Which of the following is NOT a characteristic of eukaryotic cells?
Binary fission
What is the term used to describe the state of harboring potentially pathogenic organisms?
Carrier state
What is the primary difference between residents and transients in the human microbiota?
Duration of colonization
What is the approximate ratio of microbial cells to human cells in the human body?
10:1
Study Notes
Microbial World
- The spectrum of infection has widened, with discoveries that certain organisms can cause disease under certain circumstances.
- Helicobacter pylori is a major cause of gastric and duodenal ulcers and is an officially declared carcinogen.
Microbiology
- Microbiology is the study of all living organisms that are too small to be visible with the naked eye.
- Microbes include bacteria, archaea, viruses, fungi, prions, protozoa, and algae.
- Microbes play key roles in nutrient cycling, biodegradation, climate change, food spoilage, disease, and biotechnology.
Classification of Microorganisms
- The major classes of microorganisms, in order of ascending size and complexity, are:
- Prions (infectious proteinaceous particles)
- Viruses (not cellular, lacking cell membranes, cytoplasm, and machinery for synthesizing macromolecules)
- Bacteria (prokaryotes)
- Fungi
- Parasites
Characteristics of Eukaryotic and Prokaryotic Cells
- Eukaryotic cells:
- Large (10-100 µm)
- Multicellular
- Nucleus present (membrane-bound)
- Mitotic division
- Membrane-bound organelles present
- Ribosomes large (80S)
- Cell wall simple (present in fungi)
- Prokaryotic cells:
- Small (0.5-5 µm)
- Unicellular
- Nucleus absent (nucleoid region)
- Binary fission
- Membrane-bound organelles absent
- Ribosomes small (70S)
- Cell wall peptidoglycan (present in all prokaryotes)
- Cytoplasm and plasma membrane are present in both eukaryotic and prokaryotic cells.
Human Microbiota
- The presence of microbes on or in humans is normal and universal, with 10 times more microbial cells than human cells.
- The microbiota, formerly called the normal flora, consists of microorganisms, mainly bacteria, that colonize various body sites in healthy individuals.
- The constituents and numbers of the microbiota vary in different areas of the body and at different ages and physiological states.
- Microorganisms of the microbiota may have a symbiotic relationship that benefits the host or may simply live as commensals with a neutral relationship to the host.
- Members of the human microbiota may stay for highly variable periods, including:
- Residents: strains that occupy a niche indefinitely.
- Transients: acquired from the environment, establishing themselves briefly before being excluded by competition or the host's defense mechanisms.
Explore the world of microorganisms, from harmless to disease-causing, and the impact of bioterrorism on infectious diseases.
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