Learning Objectives:
You should be able to:
- describe the major differences between eukaryotic and prokaryotic cells and explain why it is important to know the differences.
- use bacterial nomenclature properly.
- describe the phenotypic features used to classify bacteria.
- explain the difference between phenotypic and genotypic classification of bacteria and the advantages and limitations of each.
- describe how the Gram stain is done, what a Gram-negative vs. Gram-positive cell looks like microscopically, and how the Gram stain is used in clinical medicine.
- list the major structural features of bacteria and their functions in the bacterial cell and in disease production.
- describe the major structural differences between Gram-negative cells and Gram-positive cells.
- explain why some bacteria cannot be Gram-stained and describe the alternative methods that must be used to identify them.
- describe the basic structure of peptidoglycan and how lysozyme disrupts this structure.
- describe the basic structure of LPS and its role in disease production.
- describe the basic structure of teichoic acid and its role in disease production.
- describe the cellular location and functions of capsules, flagella, pili (fimbriae), and the glycocalyx and their roles in disease production.
- explain what spores are and describe the major properties of spores that relate to disease production and methods used for sterilization.
Reading Assignment:
P.R. Murray et al. 2005. Medical Microbiology, 5th edition. Elsevier/Mosby, Philadelphia, PA.
Chapter 2, Bacterial Classification
Chapter 3, Bacterial Morphology and Cell Wall Structure and Synthesis
OVERVIEW
     Classification of organisms into groups with similar features provides a means of predicting the nature of all the members of the group. However, the extreme diversity of bacteria makes it difficult to classify them into clear-cut categories, and technological advances are changing the way we have classified many bacteria in the past, in addition to identifying new species. Understanding the similarities and differences between eukaryotic and prokaryotic cells is important because it provides the basis for developing effective and selective antibacterial agents. Understanding the structure of bacterial cells is critical for appreciating the variety of ways these organisms cause disease and has led to improved methods for clinical identification of bacteria
Frequently Asked Questions
What are the major differences between eukaryotic and prokaryotic cells?
Eukaryotic cells have a defined nucleus containing their genetic material, whereas prokaryotic cells do not have a nucleus and their genetic material is free-floating within the cell. Eukaryotic cells are generally larger and more complex, containing various organelles like mitochondria and endoplasmic reticulum, while prokaryotic cells are simpler and smaller. Understanding these differences is crucial for developing targeted antibiotics that can effectively kill bacteria without harming human cells.
How is bacterial nomenclature used in microbiology?
Bacterial nomenclature follows a binomial system, similar to other forms of life, using two names: the genus and the species. For example, in Escherichia coli, 'Escherichia' is the genus and 'coli' is the species. This standardized naming system helps scientists accurately identify, categorize, and communicate about bacteria across different regions and languages.
What are phenotypic features used to classify bacteria?
Phenotypic classification of bacteria involves observable characteristics such as shape, size, color, and arrangement, as well as physiological traits like metabolism, growth conditions, and biochemical activities. These features help in identifying bacterial species and understanding their roles in different environments, including their potential to cause disease.
What is the Gram stain and how is it used in medicine?
The Gram stain is a laboratory technique used to classify bacteria into two groups: Gram-positive and Gram-negative, based on the structural differences in their cell walls. Gram-positive bacteria retain the crystal violet stain and appear purple, while Gram-negative bacteria do not and appear pink after a counterstain. This differentiation is crucial in clinical settings to guide appropriate antibiotic treatment, as Gram-positive and Gram-negative bacteria often respond differently to antibiotics.
Why can't some bacteria be Gram-stained?
Some bacteria, such as Mycobacterium species, have unique cell wall structures that do not retain the Gram stain. These bacteria require alternative staining techniques, like the acid-fast stain, to be visualized. Knowing which bacteria cannot be Gram-stained assists in choosing the right diagnostic methods for detecting specific infections.
What is peptidoglycan and why is it important?
Peptidoglycan is a structural component of bacterial cell walls, providing rigidity and protection. It is a polymer composed of sugars and amino acids. Peptidoglycan is crucial because it is targeted by antibiotics like penicillin, which inhibit its synthesis, leading to bacterial cell death. Understanding peptidoglycan structure helps in developing new antibacterial therapies.
What role does LPS play in disease production?
Lipopolysaccharide (LPS) is a component of the outer membrane of Gram-negative bacteria. It acts as an endotoxin, triggering strong immune responses in humans, which can lead to inflammation and septic shock. Recognizing the role of LPS in disease helps in understanding bacterial pathogenesis and developing treatments to mitigate its effects.
What are bacterial spores and how do they relate to disease?
Bacterial spores are dormant, resilient forms of bacteria that can survive harsh conditions like heat and desiccation. They are produced by certain bacteria, such as Bacillus and Clostridium species, and are significant in disease because they can persist in the environment and resist sterilization efforts. Understanding spore formation is essential for controlling infections and ensuring effective sterilization practices.