Bacteria Flashcards
What are bacteria?
Micro-organisms that cause infectious disease
Single-celled prokaryotes
How do bacteria reproduce?
Binary fission
Describe the three membranes of bacteria.
Bacteria cells consist of three membranous layers; a capsule, a cell wall and an inner membrane.
The capsule is the outermost layer of the bacteria cell, not all bacteria have one.
The cell wall is the layer underneath, with the inner membrane being the innermost layer.
Describe the structure of bacteria.
Within the bacteria there is cytoplasm, ribosomes and a single chromosome. The chromosome is free within the cell as there is no nucleus present.
Flagellum - threadlike structure that enable them to swim.
Fimbria - a series of thread-like projections that can attach to their external environment.
What are the two types of bacteria?
Gram-positive
Gram-negative
What is the structural difference between gram-positive and gram-negative bacteria?
Gram-negative bacteria have an additional outer membrane that is composed of lipopolysaccharides and proteins.
Gram-positive bacteria have a thick peptidoglycan layers and gram-negative bacteria have a thin peptidoglycan layer
How do gram-positive bacteria appear in gram stain microscopy?
Purple
How do gram-negative bacteria appear in gram stain microscopy?
Red
Describe the steps involved in gram stain microscopy.
- Spread bacterial culture on a glass slide and fix the sample to the slide by heating it with a Bunsen flame.
- Add crystal violet, which all bacteria take up and all stain purple.
- Add iodine, which results in crystal violet complexes forming. These complexes form in all of the bacteria cells.
- Add acetone alcohol, which only decolourises gram-negative bacteria cells.
- Add a secondary solvent to the slide, which stains all the decolourised gram-negative bacteria cells red.
- Airdry the glass slide and view it under the microscope.
What are the advantages of gram stain microscopy?
Quick - early indication of bacteria causing infection and we can prescribe an effective antibiotic
Simple
Inexpensive
What are the two shapes of bacteria?
Cocci (spherical)
Bacilli (rod)
What do the cell walls of bacteria consist of?
Plasma membrane, which contains a cross link of penicillin binding proteins. These proteins allows passage of molecules across the cell wall.
Above plasma membrane there is a peptidoglycan layer, which adds strength and shape. Thicker in gram-positive than gram-negative
ONLY gram-negative bacteria contain an outer membrane, which is made up lipopolysaccharides and penicillin binding proteins. Lipopolysaccharides allow a strong immune response
What is the periplasm space?
The space in gram-negative bacteria between the inner and outer membrane in the ell wall.
What are the two types of capsules?
Rigid
Slimy
What is the role of a capsule?
Preventing phagocytosis and allowing them to evade the immune response
What are the four types of flagellum?
Type A - consists of one single flagella
Type B - consists on multiple flagella, all on the same side
Type C - consists of two flagella, one on either side
Type D - consists of multiple flagella all over
What structure in bacteria allow biofilm formation?
Fimbriae, as they are Abel to attach to other bacteria cells and pull them together to form a community
What is biofilm formation?
A community of bacteria.
What are spore-forming bacteria? What are spores?
Bacteria that form spores.
Spores are the dormant form of bacteria and are highly resistant to physical and chemical influences, allowing them to live for a long period of time
What are streptococci bacteria?
Chained cocci bacteria
What are staphylococci bacteria?
Clustered cocci bacteria
How do we classify between streptococci gram positive bacteria?
Haemolyse test
What streptococci gram-positive bacteria partially haemolyse? What effect do they have on agar?
Alpha
Turn agar green
What streptococci gram-positive bacteria completely haemolyse? What effect do they have on agar?
Beta
Turn agar clear
