Microbiology Lecture 5 Flashcards
Do bacterial growth curves exhibit symmetry? What are they like?
Not symmetrical, they can tolerate temperatures below their optimal, but will quickly die above.
What is the optimum temperature for mesophiles?
37C
What 3 factors limit bacterial growth when temperatures are lower than the optimum?
- Cell membrane loses fluidity
- Enzymes stop working
- Transport slows down
What 3 factors limit bacterial growth when temperatures are higher than the optimum?
- Protein denaturation
- rRNA denaturation
- Cell membrane becomes too fluid
Do cycles of freezing and thawing encourage or inhibit bacterial growth, and why?
Inhibits, as the ice crystals poke holes in the cells of the bacteria’s host, releasing nutrients and encouraging growth.
Are pH growth curves symmetrical? What is the typical tolerance range for bacteria?
Yes, they tend to be.
Most grow between 6.5-7.5
When bacterial cultures grow, does pH tend to increase, or decrease? Why is this so? What effect does this have? What can be done to avoid this when culturing them?
They tend to release acids, resulting in decreasing pH. These acids interfere with their growth.
Buffers can be used to minimise this.
True or false
Yeast and fungi do not tolerate low pH well.
False
Do mycoplasma have a true cell wall?
No.
Define moderate halophile.
Only grows when a minimum amount of salt exists, cannot grow in its complete absence.
Define halotolerant.
Do not require salt to grow, but can tolerate a certain range only.
Define aW.
Amount of water free to react.
Which organism grows well at low aW?
Fungi.
Define aerobe.
Requires oxygen for growth.
Define anaerobe.
Grows only in the absence of oxygen.
Facultative anaerobe.
Will grow with or without oxygen.
Which bacteria is responsible for allowing anaerobes to live in the bowel? How does this work out?
E. coli. Is a facultative anaerobe that will use up all the oxygen in the bowels, depriving it entirely.
This allows anaerobes to grow.
E. coli is a facultative anaerobe, and will continue to grow regardless.
Define strict/obligate aerobe.
Strictly requires oxygen for growth, used in oxidative metabolism.
Name the shape and gram status of pseudomonas, and its oxygen requirements.
Strict aerobe
Gram negative rod
What kind of environment do strict anaerobes require?
Reducing environment.
Do strict anaerobes die on exposure to air?
Yes.
Can strict anaerobes tolerate oxygen exposure?
Yes, but only some.
How do strict anaerobes derive energy?
Fermentative metabolism.
Do strict anaerobes have an electron transport pathway?
No.
Define aerotolerant anaerobe.
Grows the same in O2 as it does in anO2
Do facultative anaerobes grow better with or without oxygen?
With.
Define capnophilic.
Prefers the presence of 10% CO2
Define microaerophilic.
Requires less oxygen than atmosphereic O2, but not 0%.
Define the lag phase, and what occurs during this phase.
Bacterial numbers are constant. Bacteria are preparing for growth by making the required proteins for growth and nutrient uptake.
Define the exponential growth phase, and what occurs during this phase.
Cell numbers double at a constant rate.
Define the stationary phase, and what occurs during this phase.
If nutrients are limited, growth cannot continue indefinitely. Net number remains constant.
Define the death phase, and what occurs during this phase.
No cell growth, cells begin to die and may lyse.
Describe the morphology, gram status, and oxygen requirements of campylobacter.
Gram negative curved rod.
Capnophilic.
Describe the morphology, gram status, and oxygen requirements of E. coli.
Gram negative rod.
Facultative anaerobe.
Describe the morphology, gram status, and oxygen requirements of lactobacillus.
Gram positive rod.
Aerotolerant anaerobe.
Describe the morphology, gram status, and oxygen requirements of clostridium.
Gram positive rod.
Strict anaerobe.
What 4 symptoms are caused by clostridium?
Gas gangrene
Botulism
Tetanus
Hospital acquired diarrhoea
Describe the morphology, gram status, and oxygen requirements of pseudomonas.
Gram negative rod.
Strict anaerobe.
