16 Questions
What are the three basic groups of bacteria based on shape?
cocci, bacilli, and spirochetes
What is the function of the bacterial cell wall?
It provides protection to the cell against osmotic lysis, confers rigidity, protects the cell from toxic substances, is the site of action of several antibiotics, and contains virulence factors.
What are the specific growth properties based on which bacteria are classified?
Aerobic (require oxygen), Anaerobic (cannot grow in presence of oxygen), or Facultative anaerobes (grow in presence or absence of oxygen)
What is the size range of bacteria?
0.2 to 5 μm
Which type of bacteria are surrounded only by a cell membrane?
Mycoplasma
Give an example of cocci that occur in grapelike clusters.
staphylococci
What is the major difference in the thickness of the peptidoglycan layer between gram-positive and gram-negative bacteria?
The peptidoglycan layer is much thicker in gram-positive (50–100 layers thick, 16–80 nm) than in gram-negative bacteria (1–2 layers, 2 nm thick).
What is the function of Teichoic Acid in the cell wall of gram-positive bacteria?
Teichoic Acid induces inflammation and septic shock when caused by certain gram-positive bacteria.
Which part of the gram-negative bacteria's cell wall is unique to them and is absent in gram-positives?
Lipopolysaccharide (LPS) is unique to gram-negative bacteria and absent in gram-positives.
What are the three parts that make up Lipopolysaccharide (LPS) in gram-negative bacteria?
Lipid A or the endotoxin, Core polysaccharide, and O side chain (or O antigen).
What is the function of the Outer Membrane in gram-negative bacteria's cell wall?
The Outer Membrane serves as a protective barrier to the cell and contains outer membrane proteins (OMP) or porin proteins that help in transport of smaller molecules.
What unique feature of mycobacteria's cell wall prevents the penetration of dyes used in the Gram stain?
The large amounts of high molecular weight lipids (mycolic acids) attached to polysaccharides and proteins prevent the penetration of dyes used in the Gram stain.
What are the two major activities of Lipid A or the endotoxin in gram-negative bacteria's Lipopolysaccharide (LPS)?
Lipid A or the endotoxin has endotoxic activities, such as pyrogenicity, lethal effect, tissue necrosis, and anti-complementary activity.
What is the role of the periplasmic space in gram-negative bacteria?
The periplasmic space lies between the outer-membrane layer and the cytoplasmic membrane in gram-negative bacteria and in some species, it is the site of enzymes called βlactamases that degrade penicillins and other βlactam drugs.
What is the property of the O side chain (or O antigen) of Lipopolysaccharide (LPS) that makes it useful for serotyping bacteria?
The O side chain (or O antigen) greatly varies in composition between bacterial strains, making it a major surface antigen used for serotyping bacteria.
What is the main difference in the staining process between the Gram stain and the acid-fast stain for mycobacteria?
The dyes used in the Gram stain do not penetrate into (do not stain) mycobacteria, whereas the acid-fast stain does stain mycobacteria.
Study Notes
Bacterial Shape and Classification
- Bacteria are classified into three basic groups based on shape: bacilli (rods), cocci (spheres), and spirilla (spirals)
Cell Wall Function and Structure
- The bacterial cell wall provides structural support, maintains cell shape, and allows the cell to withstand osmotic pressure
- The cell wall is composed of peptidoglycan (also known as murein) and is thicker in gram-positive bacteria (20-40 layers) than in gram-negative bacteria (1-2 layers)
Bacterial Growth Properties
- Bacteria are classified based on their growth properties, including temperature range, pH range, and oxygen requirements
Bacterial Size Range
- Bacteria range in size from 0.5 to 5.0 μm in length and 0.2 to 1.0 μm in width
Cell Membrane-Bound Bacteria
- Mycoplasma is an example of bacteria surrounded only by a cell membrane, lacking a cell wall
Cocci
- Staphylococcus aureus is an example of cocci that occur in grapelike clusters
Peptidoglycan Layer
- The peptidoglycan layer is thicker in gram-positive bacteria (20-40 layers) than in gram-negative bacteria (1-2 layers)
Teichoic Acid
- Teichoic acid is a component of the cell wall in gram-positive bacteria, involved in cell wall synthesis and maintenance
Gram-Negative Cell Wall
- The outer membrane is a unique component of the gram-negative bacterial cell wall, absent in gram-positive bacteria
Lipopolysaccharide (LPS)
- LPS is composed of three parts: Lipid A, Core polysaccharide, and O side chain (or O antigen)
- Lipid A is also known as endotoxin
- The O side chain is responsible for serotyping bacteria
Outer Membrane Function
- The outer membrane is semi-permeable and regulates the passage of nutrients and waste products
Mycobacterial Cell Wall
- The mycobacterial cell wall is unique due to the presence of mycolic acid, which prevents the penetration of dyes used in the Gram stain
Lipid A (Endotoxin) Functions
- Lipid A (endotoxin) is involved in inducing inflammation and activating the immune response
Periplasmic Space
- The periplasmic space is a region between the inner and outer membrane of gram-negative bacteria, involved in nutrient uptake and waste removal
Acid-Fast Stain
- The acid-fast stain is used specifically for mycobacteria, as the mycolic acid in their cell wall prevents the penetration of dyes used in the Gram stain
Test your knowledge of bacteria shape and classification with this quiz. Learn about the different groups of bacteria based on shape, such as cocci, bacilli, and spirochetes. Understand the importance of bacterial arrangement and specific growth properties.
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