Block D - Microbial Growth Flashcards
What is the lag phase?
the period of adaptation and non-replication in the early stages of bacterial growth when bacteria is introduced to new conditions
Why do we use pasteurisation?
lowers microbial numbers for preventing spoilage
What is sterilisation?
kills all microbes
Name 3 methods we use to sterilise?
UV, heat, sterile filtration
How does UV light cause sterilisation?
kills bacteria by causing many mutations
How does sterilisation occur through filtration
liquid or gas is passed through a filter with a pore size small enough to block the passage of most microbial organisms. pore size is usually 0.22µL, which is effective for trapping most bacteria
Define bacteriocidal and describe what a graph would look like in terms of log cell number?
kills the bacteria, no cell growth but log cell number plateus and stays the same
Define bacteriostatic and describe what a graph would look like in terms of log cell number?
inhibits bacterial growth but does not kill bacteria, log cell number stays the same
Define bacteriolytic and describe what a graph would look like in terms of log cell number?
causes cell lysis and death via rupture of the cell wall/membrane, no growth and log cell number decreases
Define antibiotic? (2 marks)
-antimicrobial compound
-produced by bacteria and fungi for killing or inhibiting the growth of bacteria
What is a broad spectrum antibiotic, when is it used and give an example?
effective against a wide variety of gram postitive and gram negative bacteria and often used when the specific bacterial case is unknown. tetracycline
What are 2 risks of using broad spectrum antibiotics?
-since it targets all bacteria, it can disrupt the good bacteria in your body (such as the bacteria found in your gut)
-can lead to antibiotic resistance
What is a narrow spectrum antibiotic, when is it used and give an example?
these target a smaller, more specific group of bacteria, usually focusing on either gram-positive or gram-negative bacteria, or sometimes a single species. used when the causative bacteria has been identified. penicillin (effective against gram positive bacteria)
What are 2 risks of using narrow spectrum antibiotics?
-not effective is the causative bacteria is not know
-if multiple bacteria is involved
Name a narrow spectrum antibiotic that targets a specific species?
Isoniazid (targets Mycobacterium tuberculosis specifically)
Describe the mechanism of action for different antifungal medicines? (3 marks)
-azoles like fluconazole inhibit the enzyme 14α-demethylase, which is involved in ergostreol synthesis
-polyenes like amphotericin B bind directly to ergosterol in the fungal cell membrane, creating pores that lead to lysis
-echinocandins like caspofungin inhibit the enzyme 3 β-glucan synthase, preventing the formation of β-glucan in the cell wall. This weakens the fungal cell wall, leading to cell lysis
An autoclave is used for pasteurisation and uses ____?
heat
What is the main idea of the Red Queen Hypothesis?
the theory that suggests that organisms must constantly evolve and adapt not just to survive in their own environment, but also to keep up with the evolving strategies of other organisms, particularly their predators, prey, and competitors
What is the role of co-evolution in the Red Queen Hypothesis?
the concept of co-evolution, is where two or more species exert selective pressures on each other, leading to an ongoing cycle of adaptation
What is the main idea of the Red Queen Hypothesis?
some species evolve to lose certain functions or traits that are costly to maintain, so they “offload” these functions by relying on these species performing the functions. by doing so they can conserve energy and resources, while still benefiting from the lost function as long as other species are performing it.
What is quorum sensing?
its a form of cell to cell communication that allows bacteria to coordinate their behaviour based on their popultaion density
Quorum sensing involves the release, detection and response to signalling molecules called _______
autoinducers
Explain the role of the signalling molecules in quorum sensing (4 marks)
autoinducers accumulate in the environment as the population grows. once a certain threshold concentration of autoinducers is reached, the bacteria trigger a coordinated change in gene expression, leading to a collective behaviour that would be ineffective or inefficient if done individually
Name the most commonly studied autoinducer in Gram-positive bacteria
peptides
Name the most commonly studied autoinducer in Gram-negative bacteria
acyl-homoserine lactones (AHLs)
What’s the importance of neutral mutations?
they could be the prerequisite to an advantagous/ disadvantagous mutation, enough neutral mutations could lead to a mutation that changes the selectivity
What does the graph of adaption look like, describe it and explain why it looks the way it does.
adaptation is a step-up pattern not a straight line graph, this is because certain microbes get advantageous mutations and colonise the population (step-up)
