Bacteria Flashcards
What are some bacterial major structural components of in terms of their significance for medical microbiology and infectious diseases?
Beyond the key components of bacterial structure, there are also some “optional extras” that may be elements of the bacteria. These include: flagella. fimbria/pili, endospores etc.
What are the metabolic processes of bacteria?
Bacteria have varying methods of metabolising:
-Aerobic Respiration: oxygen
-Anaerobic Respiration: inorganic compounds
-Fermentation: organic compound
During metabolism, some bacteria produce lactic acid or any of the other end-products of glucose metabolism which can help to identify that bacteria in culture.
Explain how bacteria may be classified?
Bacteria can be either Gram Negative, Gram Positive or a third category known as Acid Fast Bacteria.
Bacteria can also be classified according to morphology/shape. They can be either cocci (round) or bacilli (rods), and are found in many forms (clusters/chains/pairs).
Bacteria are classified according to their relationship with oxygen.
What are acid fast bacteria?
ACID FAST BACTERIA
- have thick waxy walls with a peptidoglycan base layer and additional layers of arabinogalactan, mycolic acid and lipid. - confer resistance to drying and many harsh chemicals and antibiotics however because of the slow rate of uptake, they grow slowly - example: mycobacteria (M. tuberculosis)
What are endospores?
Specialised, resistant, dormant structures that do not replicate. They are resistant to heat, desiccation, UV and many chemicals and impermeable to most stains. Sporulation (Production of spores) normally occurs when growth ceases due to lack of nutrients and/or moisture in an attempt to maintain long term survival. The process of sporulation and germination are complex.
Some examples of bacteria with endospores are Clostridium tetani, C. perfrinens etc.
Explain the different relationships that Bacteria can have with air:
Strict Aerobes: require oxygen for respiration
Strict Anaerobes: killed by oxygen
Facultative Anareobes: grow with or without air
Aerotolerant Anaerobes: survive in oxygen
Microaerophiles: grow best in low concentrations of oxygen
What are the stages of bacterial relication?
Bacteria grow and replicate via binary fission, in which one bacteria becomes two in the same time that one hundred becomes two hundred.
A: Lag Phase
B: Logarithmic Phase
C: Stationary Phase
D: Death/Decline
What are capsules?
Capsules are a barrier beyond the bacterial cell wall comprising of polysaccharide material that extends from the cell surface. it cannot be washed off and gives bacteria the appearance of being shiny and larger. Capsules can be viewed via negative staining.
Some examples of bacteria that have capsules are Bacillus anthracis and Klebsiella species.
Capsules are used to protect against dehydration, contribute to the virulence of the bacteria and often protect against phagocytosis.
What are pili/fimbriae?
These are hair-like appendages made from pilin protein that are used for attachment/adhesion to other cells and each other as well as for gene transfer through ‘sex pili’ in some bacteria. They are only visible via electron microscope and are found on most Gram negative bacteria but also some gram positive.
Quite often the bacterial wall and that which a bacteria is aiming to adhere are similarly charged and adhesion is not electrostatically favored. For this reason, adhesive pili protrude from the bacterium and house adhesion proteins on the ends so as to overcome the unfavorable charge issues.
What are flagella?
A thin, long, hollow, helical filament comprised of flagellin protein that has a basal body attached to the cell wall, a hook and a filament that protrudes external to the bacterial wall. It is used for locomotion and motility. It is visible under light microscope with a special stain but generally its presence is inferred my motility.
Like the LPS in Gram negative bacteria is composed of units of O-antigen, flagella are comprised of units of H-antigen which gives an indication of the many various species/varieties of E.Coli and other bacteria there are.
