Bacterial Growth / Control and Sterilisation Flashcards
1
Q
What is the facultative mechanism of obtaining energy
A
- Facultative refers to the ability to live under more than one specific environmental condition
- Organisms obtain energy from aerobic respiration, anaerobic respiration and fermentation
- There is only one type of facultative organism (facultative anaerobes)
- Can survive with the presence or absence of oxygen
- Organisms live in external environment as well as inside the host
- Parasites can survive without the host
- Efficiency of the energy production in facultative organisms is high
2
Q
What is the obligate mechanism of obtaining energy
A
- Obligate means to be restricted to a particular characteristic
- Organisms obtain energy from aerobic respiration or anaerobic respiration or fermentation
- There are two types of obligate organisms (obligate aerobes and anaerobes)
- Obligate aerobes survive in the presence of oxygen, obligate anaerobes survive in the absence of oxygen
- Obligate aerobes only live in the external environment while obligate anaerobes only live inside hosts
- Parasites only survive in the presence of the host
- Efficiency of the energy production is less
- Microbe: Obtain cellular energy from bacteria, fungi and endoparasites such as protozoans and worms
3
Q
How does one transport nutrients into the cell
A
- Active Transport: Accumulation of solutes against a concentration gradient
- Transporters: Simple transport, group translocation of ABC system, energy driven (proton motive force, ATP or another energy rich compound)
- Simple Transport: Driven by proton motive force, either symport (solute and H co-transported in one direction) or anti-port (solute and H transported in opposite directions)
- Iron Metabolism Siderophores: Bacteria have an essential requirement for iron, have specialised Fe- binding proteins, capture free Fe released as a result of cell death
4
Q
What is bacterial growth and what are the requirements
A
- Bacterial Growth: Increase in number of cells not cell size, requirements are both chemical and physical
- Chemical Requirements: Nutrients and trace elements, oxygen (or lack of) and organic growth factors
- Physical Requirements: Temp, pH and osmotic pressure
5
Q
What are some of the chemical requirements
A
- Chemicals and elements utilised for bacterial growth are referred to as nutrients or nutritional requirements
- Some chemicals are required in large amounts (C,H,O,N,S,P) and others in trace amounts (Zn, Co, Cu, Mo)
- Found in the form of water, inorganic ions, small molecules and macromolecules
- Living cells require both an energy and carbon source to build necessary components for all cell structures
- Organic GF: Organic compounds obtained from environment (vitamins, AA, purines, pyrimidines)
6
Q
Describe temperature as a physical requirement
A
- Minimum, optimum and maximums growth temp
- Organisms are placed in three large groups based on preferred growth temperatures (no strict cutoff, overlapping)
- Minimum: Membrane gelling, transport processes so slow that growth cannot occur, 0-10°C, many bacteria survive, some grow, very few pathogens
- Optimum: Enzymatic reactions occurring at maximal possible rate, 15-55°C (danger zone) rapid growth
- Maximum: Protein denaturation, collapse of cytoplasmic membrane, thermal lysis, 60-70°C, destroy most microbes (lower temperatures take more time to destroy)
- Classification: Psychrophile (0 - 15°C), mesophiles (15 - 50°C), thermophiles (50 - 80°C), extreme thermophiles (can even thrive at near boiling temperatures)
7
Q
Describe microbial life at high temperatures
A
- Thermophiles inhabit moderately / intermittently hot environments, thermal gradients form along edges of hot environments
- Distribution of microbial species along the gradient is dictated by organism’s biology
- Enzymes and proteins function optimally at high temperatures, features that provide thermal stability.
- Critical amino acid substitutions in a few locations provide more heat-tolerant folds.
- Increased number of ionic bonds between basic and acidic amino acids resists unfolding in the aqueous cytoplasm, highly hydrophobic interiors
- Production of solutes helps stabilise proteins modifications in cytoplasmic membranes to ensure heat stability
8
Q
Describe microbial life at low temperatures
A
- Extremophiles: Organisms that grow under very hot or very cold conditions
- Psychrophiles: Organisms with optimal growth temp ≤ 15°C, max ≤ 20°C, min ≤ 0°C, inhabit constantly cold environments
- Psychrotolerant: Organisms that can grow at 0°C but have optimal of 20-40°C, widely distributed in nature than psychrophiles, isolated from soils and water in temperate climates / food at 4°C
- Cytoplasmic membranes function at low temp, high unsaturated and shorter-chain fatty acid content, some polyunsaturated fatty acids, which remain flexible at very low temperatures
- Cold shock proteins (chaperones)
- Cryoprotectants (e.g., antifreeze proteins, certain solutes) prevent formation of ice crystals
- Exopolysaccharide cell surface slime
9
Q
Describe oxygen as a physical requirement
A
- Oxygen Metabolism: Byproducts can damage membranes and toxic to cells, must neutralise metabolites
- Anaerobic Bacteria: O2- - metabolism - toxic products (O2-, OH, H2O2) - no detoxifying pathway - bacterial death
- Aerobic / Facultative Bacteria: O2 - metabolism - toxic products (O2, OH, H2O2) - detoxifying pathway (superoxide dismutase, catalase, peroxidase) - nontoxic products (H2O, O2)
- Enzymes: Protect bacteria from the effects of oxygen and enable bacteria to survive in oxygen
- O2- + O2- + 2H+—(superoxide dismutase)—H2O2 + O2
- H2O2—(catalase)— H2O + O2
- H2O2 + NADH + H+ —(peroxidase)— 2H2O + NAD
10
Q
What is an obligate aerobe vs anaerobe
A
- Obligate Aerobes: Grow in presence of oxygen, no fermentation, oxidative phosphorylation, example (Mycobacterium tuberculosis and Bacillus subtilis)
- Obligate Anaerobe: No oxidative phosphorylation, fermentation, killed by oxygen, lack enzymes (superoxide dismutase, catalase, peroxidase), example (Clostridium tetani and Clostridium perfringens)
11
Q
What is a facultative and aerotolerant anaerobe and microaerophile
A
- Facultative Anaerobe: Can grow without oxygen but uses oxygen if it is present, can also use fermentation and aerobic respiration, survives in oxygen, example (E.coli, Enterobacter aerogenes)
- Aerotolerant Anaerobe: Cannot use oxygen for their growth but are not harmed by it, respire anaerobically, not killed by oxygen, example (Lactobacilli and Streptococci, Clostridium SPP)
- Microaerophile: Require lower concentrations of oxygen (2-10%), grow in low oxygen concentration, killed in presence of high oxygen concentrations (H. pylori)
12
Q
Describe pH as a physical requirement
A
- Neutrophils: Most bacteria grow best between pH 6.5-7.5
- Acidophils: Low pH can be used as a food preservation technique, tolerant of acidity
- Alkaliphils: Organisms that grow best at high pH (>9), moulds and yeast grow over a wide pH range than bacteria (optimal pH 5-6)
- Internal pH: Must stay relatively close to neutral, despite external pH being highly acidic or basic
- As low as 4.6 and as high as 9.5 in extreme acido- and alkaliphils, respectively
- Urease Enzyme: Can generate NH3 and CO2 from urea which is released into the environment to increase pH (H. pylori)
13
Q
Describe osmotic pressure as a physical requirement
A
- Osmotic Pressure: Pressure exerted on bacterial cells by their environment, effects the growth of microorganisms
- Typically, the cytoplasm has a higher solute concentration than the surrounding environment; water moves into the cell (positive water balance)
- When a cell is in an environment with a higher external solute concentration, water flows out unless the cell has a mechanism to prevent
- Plasmolysis: Hypertonic environments, increase salt or sugar, useful in food preservation
- Bacteria: Cell wall enables resistance to forces in a hypotonic, less able to deal with a hypertonic
- Facultative Halophiles: Salt tolerant, can handle a higher salt environment (Staphylococcus)
- Halophiles: Organisms adapted to living in high salt concentrations, grow best at reduced water potential
- Extreme Halophiles: Organisms that require high levels (15–30%) of NaCl for growth
- Halo tolerant: Organisms that can tolerate some reduction in water activity of environment but generally grow best in the absence of the added solute
14
Q
What is exponential growth and generation time
A
- Exponential Growth: Growth of a microbial population via a mathematical pattern in which cell numbers double within a specific time interval, initially slow but increases at a faster rate,
- When a cell is placed on a solid growth surface, like an agar petri dish, it will begin to divide
- Generation Time (g) = t / n, where t is duration of exponential growth (minutes, hours, days) and n is the number of generations during exponential growth
- Colony: ‘Pile’, all cells in such a colony are identical
15
Q
What are the stages of the microbial growth cycle
A
Lag Phase:
- Interval between when a culture is inoculated and when growth begins, transporting of molecules into the cell
- Accumulation of substances to allow for growth to occur
- Adapting to environment
- Time needed for biosynthesis of new enzymes and to produce required proteins
Exponential Phase:
- Cells in this phase are typically in the healthiest state, most active growth phase
Stationary Phase:
- Growth rate is zero, either an essential nutrient is used up or waste product accumulates in medium
Death Phase:
- If incubation continues after cells reach stationary phase, the cells will eventually die
- Cell proliferation = cell death
