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Microbiology > Bacterial growth and population control > Flashcards

Bacterial growth and population control Flashcards

1
Q

What is the process of binary fission in bacteria?

A

chromosomal replication, nucleoid occlusion and separation.

Cytokinesis - via constriction or parietal septum.

There is a gradient of Min proteins, where Min proteins are concentrated at poles of cell.

In the centre of cell there is Nucleoid occlusion by proteins.

Min proteins at the pole inhibit the formation of Z-ring from filamentous FtsZ proteins (Tubulin homolog).

In the centre, where no Min proteins, FtsZ can form contractile Z rings.

Then contractile focrce to pinch it in half.
(E.COLI)

OR
Can guide the synthesis of Parietal septum to separate two cells apart.
(BACILLUS SUBTILIS)

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1
Q

What is the definition of growth?

A

Cell growth: Increase of cell size.

Microbial growth =
Increase in no. of cells in population

Scissiparity - binary fission

Asexual reproduction

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2
Q

In A population growth curve, what can be use don Y axis?

A

CFU - colony forming units.

no. of cells.

Optical density at 600nm.

Biomass.

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3
Q

What are the stages of a population growth curve?

A

Latency period:

Exponential phase

Stationary phase

Decline

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4
Q

What are properties of latency phase of population growth curve?

A

Total no. of cells is equal to inoculum.

Total cell number, Nt, is constant and minimal.

LAtency period depends on environmental conditions

Cell activity is preparing for next divisions.
= By synthesising inducible enzymes to metabolise new constituants and restauration of altered enzymes.

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5
Q

What are the properties of the Exponential stage of Growth curve?

A

All cells dividing.

Growth follows exponential model.

Growth rate, u = ln 2/G

(natural log of 2/generation time)

G = generation time

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6
Q

What are the properties of the staionary phase of Growth curves?

A

In a non-renewed medium, glycolytic metabolism lowers pH of medium.

Toxic excretions accumulate.

Lack of nutrients.

(Total numbre of cells depends on medium “Richness” and culture volume…)

Some cells stop dividing, those that continue compensate for the cells which die and autolyse.

Physiological changes like sporulation.

= Nt is constant.

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7
Q

What are the properties of Decline phase of growth curve?

A

In a non-renewed medium, glycolytic metabolism lowers pH of medium.

Toxic excretions accumulate.

Lack of nutrients.

= No. of viable cells now decreasing, with a high mortality rate.

Cells dying and autolysing.

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8
Q

How can properties of cells change depending on population age?

A

Physiological properties of cells changes over growth curve.

Membrane permeability and growth are maximal in young populations.

With this greater permeability, comes greater susceptibility to antibiotics and GRAM staining is more reproducible.

In older populations, membrane permeability is reduced, so is antibiotic sensibility.
Gram staining is more variable and growth is limited.

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9
Q

Why are older culture populations less susceptible to antibiotics?

A

Reduced membrane permeability.

Reduced growth rate - growth is limited.

Therefore, reduced metabolism:

Antibiotic targets not in action =

Tetracyclin for ribosomes, chloramphenicol etc.
Penicillins for cell wall…

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10
Q

How can growth curves be made continous?

A

Continous growth to extend the growth phase.

Renewing medium - to remove waste products of metabolism, raise pH, increase nutrient availability,

= Using a chemostat.
= Well stirred, and topped up continuously with fresh media.

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11
Q

What is Generation time (G)?

A

Time required for reproduction of a bacterium to give 2 daughter cells.

Assumig that all bacteria divide syncrhonously, then time for doubling of population.

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12
Q

What is the equation for calculating Generation time, G?

A

G = time / n

The duration during which bacteria multiply n times.

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13
Q

What is the equation for calculating total number of cells?

A

Final no of cells (NT) = Initial no. (NI) * 2^ n

n = no. of generations.

NT = NI * 2^no. of generations

Nt = NI * 2 (time/G)

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14
Q

How to calculate growth rate through logarithm function?

A

Put the equation to natural logarithm.

Ln (NT) = time * (Ln (2) // G) + Ln (NI)

Natural log of NT = change in time * (natural log of 2 / G) + natural log of NI.

= making linear.

Slope of linear part
u = growth rate
= natural log of 2/ G

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15
Q

How to use biomass?

A

Nmax (maximum no. of cells obtained)

Nmax - Ni (max-initial)

Growth yield =
Biomass produced/substrate consumed.

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16
Q

What is a cell unit (CU)

A

On solid medium, you count no. of cell units as opposed to single cells.

1 cell unit (CU) is an isolated cell/or aggregates specific to 1 strain, presenting a grouping mode/colonial strain.

A single CU is not visible to naked eye.

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17
Q

What is a CFU?

A

Colony forming unit:

A group of cells coming from 1 mother cell, and its extracellular substances.

Extracellular matrix/poly sach. constitute mots of volume - 70+%

1 CFU is visble to naked eye (1 5mm diameter can contain as many as 10^7-10^9 cells.

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18
Q

What is a biofilm?

A

A community of micro-organisms.

Aggregated in micro-colonies which adhere to a surface.
Secreting adhesive matrix and protective exopolysaccharides.

Modified biofilm phenotype of micro-organism.
= Strong resistance and adaptation.

19
Q

What is the process of biofilm formation?

A

Adhesion - irreversible with adhesins to surface.

Production of extracellular matrix, phenotype change to become matrix producers and cells start to bundle into chains and aggregate.
= COLONISATION.

Primary maturation = surface growth as monolayer.
2ndary maturation - forming multilayer colony.

Sporulation.

When conditions change, dispersal of biofilm/dissolution.

There is also different phenotypes by oxygen availability in biofilm.

20
Q

Why form a biofilm?

A

Production of extracelular matrix provides tolerance to environmental conditions - salinity, dehydration, UV.

Protection from antibodies - leads to immune failure as cannot corss ECM.

Metabolic cooperation + horizontal gene transfers - spread genes for resistance.

21
Q

What are the names of different oxygen condition-favouring cells?

(respiratory types of bacteria)

A

Obligate aerobes

Obligate anaerobes

Facultative anaerobes

Aerotolerant anaerobes.

Micro-aeorophiles - little oxygen condition.

22
Q

What are different temperature types of bacteria?

A

Psychrophilic - freezing - 15

Mesophilic = 10-45

Thermophilic = 45-70

Hyperthermophile - above 70.

23
Q

What are halophiles?

Barophiles?

A

Depending on concentration of NaCL (Salinity, with chloride)

= Halotolerant = above 0.2M NaCl = staph. aureus

Halophiles = Vibrio fischeri = 4M

Extreme halophils - Halobacterium salinarum = 5.2M

24
Q

What is sterilisation and disinfection?

The difference?

A

Sterilisation = Destroying/removing all living cells, spores and acellular units (like prions, viruses)

Disinfection - Destruction, inhibition or removal of pathogenic micro-organisms.

Disinfectants don’t sterilise an object as some viable spores/cells can remain.

25
Q

What is decontamination and Antisepsis?

Antiseptic?

A

Reducing population of micro-organisms to a considered safe level.

Antisepsis - Prevent infection of living tissue by micro-organisms.

Antiseptic agents - inhibit development of pathogenic micro-organisms when applied on a tissue.

26
Q

What are cidal and static antimicrobials?

A

Bactericidal - destroy pathogenic bacteria, but not necessarily endospores.

Bacteriostatic - Inhibit the growth of bacteria.

27
Q

How to disinfect and sterilise lab equipment?

A

UV light to disinfect surfaces in laminar flow hoods.

Sterilise growth media and glassware in Autoclaves - Humid atmosphere, 121 degrees for 30 mins.
Or in Pasteur oven (dry)

In industry, use ionising radiation to sterilise petri dishes.

bleach to disinfect surfaces, aswell as ethanol or quarternary amines,

28
Q

What is an antibiotic?

A

Substances able to inhibit the multiplication (bacteriostatic) or kill (bactericidal) micro-organisms.

Disrupt bacterial structures and functions

2/3rds of antibiotics are metabolites derived from streptomyces genus.

29
Q

What are the requirements for an efficient antibiotics?

A

Possess a specific BACTERIAL target

Remain under an active form

Access bacterial target

Effienctly inactivate target.

(Resistant strain has atleast 1 of these requirements lacking)

30
Q

What is natural resistance?

A

Intrinsic resistance - innate ability of bacterial species to resist effects of specific antibiotics - NOT a result of any genetic changes or external selective pressures:

Characteristics of the species prevent the antibiotic from working effectively .

E.G Mycoplasma - Mollicutes = beta lactams ineffective as no cell wall..

Or impermeable outer membranes

Essentially, the antibiotic target may be missing, or lack access to it for example.

= Determines the spectrum of activity of an antibiotic.

31
Q

What is acquired antibiotic resistance?

A

Bacteria that were initially sensitive to an antibiotic develop ability to resist its effects
- genetic changes/acquisition of foreign resistance genes via HGT.

Selective pressure for resistant bacteria.

Target may become inaccessible, or antibiotic inactivated, or target dissappears/modified.

32
Q

How is acquired resistance revealed?

A

Laboratory testing with MIC or antibiograms.

33
Q

What are mechanisms for acquired resistance?

A

Impermeability of PM/outer membrane - removal of porins…

Hyperexpression of active efflux systems.

Enzymatic hydrolysis - Beta lactamases.

Modification or protection of antibiotic target.

= ViA HGT, plasmids/integrons/transposons.

34
Q

What is the purpose of a vaccine?

A

To induce immunological memory.

Induce an immune reaction to produce IgG antibodies.
Such that during a second exposure to the antigen, the production of IgG antibodies is more rapid and intense

Due to acquired immunity built during first exposure.

35
Q

What are the 4 types of vaccines?

A

Inactivated vaccines - POLIO

Vaccine subunits - Heptatitis B

Attenuated living vaccines - Measles, mumps.

Inactivated toxins - Diptheria.

36
Q

What are the pros and cons of Inactivated vaccines?

A

Can be easily stored and transported.

Low-risk to causing an infection.

However, can be at risk of inducing low immunogenecity.

Requires adjuvants and multiple vaccine shots.

EXAMPLE POLIOMYELITUS VACCINE

(SV40 due to monkey culture)

37
Q

What are the pros and cons of Subunit vaccines?

A

EXAMPLE = HEP B

Low risk of a secondary reaction.

IMMUNOCOMPROMISED people can use!

Can be difficult to produce - stabilisation of relevant antigen

Low immunogenecity - induce a weaker immune response by lacking pathogens full structure.

Requires adjuvants to enhance immune response - can introduce side effects.

Genetic code for antigen is inserted into yeast cell - allowed to ferment, mass produce and then lysed.

38
Q

What are the pros and cons of living attenuated vaccines

A

MMR, measles, mumps

Can provide lasting protection after single/two doses.
= Fewer doses
As closely mimics the natural infection

Induces humoral (IgG and cell mediated immunity)

Reduced cost.

In vulnerable individuals, there is a risk of reversion to pathogenic form.

Rquires freezing/freeze-drying.

Pathogen is grown in non-ideal conditions/genetically modified to reduce virulence.

39
Q

What are pros and cons of Inactivated vaccines?

A

DIPTHERIA

Cannot propagate.

Stable and easier to distribute.

However can require multiple shots and adjuvants.

40
Q

What is the process of an mRNA vaccine?

A

COVD-19 vaccine

mRNA expressing the antigen of interest/covid spike protein.

mRNA is modified so that it is more stable and avoids non-specific immune reactions..

mRNA encapsulated in vector of lipid nanoparticles

But requires very cold freezing storage.

41
Q

What are replicative vs non-replicative viruses vaccines?

A

Replicative viruses are modifeid, non-pathogenic forms of virus.

Virus penetrates cells to produce antigens.

= A living, attenuated vaccine.
= Measles

Non-replicative viruses are modified so that they do not replicate, but can still penetrate cells to produce antigens.

= Adenovirus.

42
Q

What are the benefits of vaccines?

A

Elimination of infectious agents - eradication of smallpox.

Radical reduction in high rate of mortality diseases…. Polio, measles.
Particularly for children.

Preventative - reduces use of antibiotics and other treatments.

Control of epidemics and protection against specific disease.

43
Q

What are and How to form inactivated vaccines?

A

Cholera vaccine

An inactivated/killed pathogen to trigger an immune response without causing disease.

Inactivated so it cannot replicate.

Formaledhyde, heat/radiation etc.

44
Q

What are toxoid vaccines?

A

Toxoid vaccines are attenuated, inactivated form of toxins used to prevent recipient from disease, but not infection…

Tetanus toxin - inactivated with formaledhyde.

Activation of B cell, IgG humoral response to antigenic part of toxoid.

Microbiology (9 decks)

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