Bacterial Growth, Nutrition and Identification Flashcards
List 10 criteria for bacterial classification.
1 - Gram stain.
2 - The proportion of the genome formed of guanine + cytosine.
3 - Growth temperature.
4 - Ability to form heat stable spores.
5 - Electron acceptors for respiration.
6 - Photosynthetic ability.
7 - Motility.
8 - Morphology.
9 - Ability to use various carbon and nitrogen sources.
10 - Special nutritional requirements.
List the taxonomic hierarchy for the three-domain system.
1 - Domain.
2 - Kingdom.
3 - Division.
4 - Class.
5 - Order.
6 - Family.
7 - Genus.
8 - Species.
List 7 methods of identification of bacteria.
1 - Antibiotic susceptibility.
2 - Whole genome sequencing.
3 - Microscopic morphology.
4 - Antigenic properties.
5 - Cultural characteristics.
6 - Biochemical reactions.
7 - Typing.
List the steps involved in gram staining.
1 - Application of crystal violet.
2 - Application of iodine (mordant).
3 - Alcohol wash (decolourisation).
4 - Application of safranin (counterstain).
What is the function of a mordant?
To fix the dye to the bacteria.
How do gram positive and negative bacteria stain?
- Gram positive stain purple (retain the dye).
- Gram negative stain pink (lose the dye upon decolourisation).
What does the term ‘coccus’ tell you about the morphology of a bacterium?
Indicates a round shape / clusters.
What does the term ‘bacillus’ tell you about the morphology of a bacterium?
Indicates a rod-like shape.
List 3 properties of Staphylococcus aureus.
1 - Gram positive.
2 - Coccus.
3 - Aerobic.
List 3 properties of the Clostridium species.
1 - Gram positive.
2 - Bacillus.
3 - Anaerobic.
List 3 properties of B. fragilis.
1 - Gram negative.
2 - Bacillus.
3 - Anaerobic.
List 3 properties of the shigella family of bacteria.
1 - Gram negative.
2 - Bacillus.
3 - Aerobic.
List 3 properties of Streptococcus pneumoniae.
1 - Gram positive.
2 - Coccus.
3 - Anaerobic.
List 3 properties of Neisseria gonorrhoeae.
1 - Gram negative.
2 - Diplococcus.
3 - Aerobic.
What are higher bacteria?
Bacteria with a relatively complex organisation.
List 2 examples of higher bacteria and the disease caused by each.
1 - Mycobacterium tuberculosis (causes TB).
2 - Mycobacterium leprae (causes leprosy).
Define acid-fast bacteria.
What makes bacteria acid-fast?
- Bacteria that are resistant to decolourisation by an acid.
- These bacteria have complex cell walls that contain large amounts of lipid substances known as mycolic acids.
Give an example of a genus of bacteria that is acid-fast.
Mycobacterium.
What does the term ‘spirochete’ tell you about the morphology of a bacterium?
Indicates a flexible, spirally twisted shape.
List 3 properties of Treponema pallidum (syphilis).
1 - Gram negative.
2 - Spirochete.
3 - Aerobic.
Why are Mycoplasma pneumoniae resistant to penicillins?
Because they lack peptidoglycan.
Why is the Chlamydiae phylum of bacteria known as obligate intracellular parasites?
Because they require host ATP (hence obligate intracellular).
Define bacterial growth.
The orderly increase in the sum components of an organism (not an increase in cellular size!).
List the phases of growth for bacteria.
1 - Lag.
2 - Log.
3 - Stationary.
4 - Death.
Define dry cell weight.
The weight left when a cell’s water content has been removed by heating.
What is most bacterial dry weight comprised of?
Organic matter comprised of macromolecules linked by anhydride bonds.
List 2 sources of energy for medically relevant bacteria.
1 - Fermentation, e.g. of sugars.
2 - Respiration.
List 2 sources of carbon for bacteria.
1 - CO2.
2 - Organic carbon, e.g. glucose.
What is the primary source of nitrogen for bacteria?
Ammonia (e.g. in soil).
List 2 sources of sulphur for bacteria.
1 - Dissolved sulphate.
2 - Found in cysteinyl and methionyl side chains of proteins.
Give an example of a use of sulphur in bacteria.
Used to form co-enzymes.
List 4 uses of phosphorus.
1 - Required for ATP production.
2 - Required for nucleic acid production.
3 - Required to phosphorylate proteins.
4 - Required for coenzymes such as NADP.
What is the primary use of minerals (such as Mg2+, Ca2+ and Fe2+) in bacteria?
Enzyme function.
Define siderophore.
A molecule present in microorganisms that facilitates iron uptake.
At which pH do most microorganisms grow best?
6-8.
At which temperature do most pathogenic bacteria grow best?
30-37 degrees celsius.
Define facultative anaerobe.
Bacteria that can grow in both the presence or absence of oxygen.
Why do most microbes express superoxide dismutase and catalase?
- To manage oxygen toxicity:
- Catalase converts hydrogen peroxide (H2O2) into water and oxygen.
- Superoxide dismutase converts superoxide (O2-) into H2O2, which must be broken down by catalase.
What type of molecule is agar?
Why is it used as a medium for bacterial growth?
- A polysaccharide.
- It is used as a medium for bacterial growth as it is resistant to antibiotic action.
Define differential media.
Media that distinguish bacterial species from each other.
Give an example of a differential media.
Blood agar (indicates which bacteria are haemolytic).
Define selective media.
Media that suppress the growth of unwanted bacteria that may be in the same sample.
List 2 examples of media that are both selective and differential.
Explain how they work as selective and differential media.
1 - Mannitol salts agar (selective for gram positive bacteria, and bacteria that ferment mannitol show as yellow).
2 - MacConkey agar (selective for gram negative bacteria, and bacteria that ferment lactose show as pink).
How does alpha haemolysis appear differently on a blood agar culture to beta haemolysis?
- Alpha-hemolysin partially breaks down the red blood cells, leaving a greenish color behind.
- Beta-hemolysin breaks down the red blood cells and hemoglobin completely, leaving a clear zone around the bacterial growth.
List 2 examples of antimicrobial agents that are used against specific bacterial species.
For each agent, include the name of the bacterial species for which it is used.
1 - Optochin and Streptococcus pneumoniae.
2 - Bacitracin and Streptococcus pyogenes.
- These agents are not used for therapy.
Define typing.
The identification of certain strains of bacteria within a species that possess particular pathogenic properties.
