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Micro Quiz 1 > bacterial growth - notes and lecture > Flashcards

bacterial growth - notes and lecture Flashcards

1
Q

what is the generation time?

A

growth rate - time required for the population of bacteria to double
can be 20 minutes to 20 hours

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2
Q

what factors limit growth?

A

1: nutrient supplies and key resources
2: accumulation of toxic metabolic processes
3: antibiotics from neighboring microbes (or humans)
4: immune system
5: environmental conditions

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3
Q

what are the major nutrient requirements for bacterial growth? (list - 10)

A

1: carbon - to make all molecules
2: nitrogen - to make DNA and proteins
3: phosphorus - for membrane phospholipids and DNA
4: sulfur - to make proteins
5: iron - for many enzymes, esp those in metabolism
6: glucose
7: other sugars
8: peptides, proteins, and AA
9: lipids
10: organic acids and alcohols

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4
Q

what are the two main functions of nutrient sources?

A

provide energy and provide carbon for the synthesis of cellular components

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5
Q

where do many bacteria acquire AA and peptides?

A

many need to pre-formed AA

secrete proteases to allow for the uptake of extracellular proteins

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6
Q

where do bacteria acquire nitrogen?

A

AA, peptides, and proteins, but also ammonia (NH4+) and nitrate

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7
Q

where do microbes acquire their nucleotides?

A

secrete nucleases to break down available DNA and RNA

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8
Q

what is the purpose of phospholipases secreted by microbes?

A

act o n host cell membranes or lung surfactant

degrade phospholipids to provide microbes with C, N, P

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9
Q

what induces phospholipase production by microbes?

A

low phosphorus or low iron levels - because host cell lysis by phospholipase activity yields iron

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10
Q

what is the role of iron in the host-pathogen relationship?

A

host cell lysis by phospholipase from microbes yields iron
host cells can make iron-binding factors that make iron unavailable to microbes
in response, bacteria and fungi make chelators (siderophores) that extract iron from host stores

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11
Q

what creates pathogenesis due to microbes?

A

results from microbes accessing host nutrients

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12
Q

what are bacterial growth factors?

A

organic (C) compounds that are not metabolized to supply energy but make metabolites that the bacterium can’t synthesize on its own
not all bacteria require these to grow, and different organisms require different ones

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13
Q

what environmental conditions affect bacterial growth rates (list)

A

temperature
pH
osmotic conditions

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14
Q

how does temperature affect growth rate of bacteria?

A

each organism needs optimal temperature (unique)
most pathogens grow best at body temp
most environmental bacteria at room temp

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15
Q

how does temperature affect mycobacterium leprae growth?

A

exception to rule that pathogens prefer body temp - only grow at low temp - why you get external lesions in leprosy cases but not damage to internal organs

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16
Q

what is the optimum pH for bacterial growth

A

usually in the 6-8 range, but most commonly 7.4

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17
Q

how does pH affect where clostridium botulinum grows?

A

botulinum toxin

more of a problem in canned foods with less acidity

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18
Q

how do osmotic conditions affect the growth of bacteria?

A

high salt and sugar (so high osmotic conditions) inhibit growth of many pathogens
but most very flexible about osmotic enviornment requirements since have cell wall to maintain internal osmotic pressure

so jams and jellies can inhibit growth

but most bacteria don’t need to regulate their internal osm very much b/c of their cell wall

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19
Q

what is the common growth medium for bacteria?

A

peptone broth with added glucose

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20
Q

what is peptone?

A

peptic digest of meat - peptides and AA

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21
Q

what percentage of pathogens will grow on blood agar?

A

90%

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22
Q

how would you attain pure cultures of bacteria (in terms of medium for growth)?

A

allows observation of colonial morphology
must grow bacteria on solid medium
add agar to liquid media

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23
Q

what can the size of a bacterial infection tell you clinically?

A

if there is an infection

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24
Q

should you see bacteria in clinical samples in a healthy patient?

A

in some, such as CSF, no

in others, such as urine, yes

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25
Q

how would you measure cell number using optical measurements?

A

use optical measurements of cell mass
small particles scatter light in proportion to their cell density (so this is basically just spectroscopy)
low cell densities can’t be detected
can correlate amount of scattered light with cell number

26
Q

what are four ways you could use to measure cell number? (list)

A

1: optical measurements
2: determination of metabolic activity
3: direct cell count
4: viable or plate counts

27
Q

how would you measure cell number using metabolic activity?

A

measure rate of production of metabolic products such as CO2 or ATP

28
Q

how would you measure direct cell number?

A

direct counting in a counting chamber in a microscope
includes viable and nonviable cells
not used often cause need really high concentrations
but even if a few bacteria are seen, indicates infection since so many bacteria are needed to see any

29
Q

how would you measure cell count using viable or plate counts?

A

single bacterium gives rise to colony on petri dish after incubation
plate sample and count number of colonies - expressed as colony forming units (CFU)

30
Q

how is the growth of bacterial cells usually graphed?

A

on a logarithmic scale as a function of time

31
Q

what are the four phases of bacterial growth? (list)

A

lag phase
log phase
stationary phase
death phase

32
Q

what occurs during the lag phase of bacterial growth?

A

metabolic activity, but no increase in numbers

cell mass and size begin to increase, macromolecules needed for growth synthsized

33
Q

what determines the length of the lag time?

A

kind of bacteria
age and size of inoculum
nature of the medium from which they were taken
nutrients present

34
Q

what occurs during the log/exponential growth phase?

A

cell numbers increase in a logarithmic manner - constant generation time
cell number and mass increase in coordinate manner - can use either paramater to determine generation time

35
Q

what does the rate of cell division during log phase depend on?

A

type of organisms
nature of medium
temperature
for aerobic organisms, rate of aeration

36
Q

what is balanced growth?

A

orderly increase in all cellular organisms
doubling of biomass is accompanied by a doubling of all other components - after size has doubled, cell divides => two identical cells

37
Q

why does the logarithimic growth phase eventually slow?

A

accumulation of waste products
exhaustion of nutrients
change in pH
decrease in O2 tension

38
Q

what occurs during the stationary phase?

A

number of cells remains the same

steady state in which some cells die an others continue to divide

39
Q

what is the typical length of time for the stationary phase?

A

can last for only a few hours but lasts for days months or years in some species and under some conditions

40
Q

what concentration do almost all pathogenic bacteria grow to during stationary phase in lab culture?

A

between 5 x 10^8 and 1 x 10^ 9 cells

41
Q

what occurs during death phase?

A

rate of death exceeds rate of reproduction - number of viable cells declines

42
Q

what is the typical length of time of the death phase?

A

varies widely between organisms
some very short whereas others weeks or years
cells often assume unusual shapes - therefore difficult to recognize bacteria in old cultures

43
Q

what is the lag phase?

A

adaptation to the host environment

44
Q

what is likely specific to exponential phase in chronic disease states?

A

slow growth may occur

45
Q

what is the consequence for the host of rapid growth during the exponential phase?

A

population of microbe may grow too fast for host to mount immune defense

46
Q

during which phase are bacteria most resistant to destruction?

A

during stationary phase, increased resistance to host defenses and antibiotics

47
Q

what are three reasons to study growth characteristics of a microbe?

A

1: identify ways to kill or inhibit microbial growth
2: to better understand disease
3: to identify and quantify a microbe in the clinical laboratory and research lab

48
Q

what are the carbon sources used by bacteria to synthesize new cells and new cell factors?

A 
glucose
other sugars
proteins, peptides, and AA
lipids 
organic acids and alcohols
ammonia and nitrate
49
Q

what do bacterial nucleases do?

A

when P levels are low, these enzymes can degrade surrounding DNA and create more for use in reproduction

50
Q

where do bacteria acquire their phospholipids?

A

degradation of host cell phospholipids => C, N, P

low P levels can induce production of phospholipase - these phospholipids can lyse host cells => Fe

51
Q

where do bacteria acquire their Fe?

A

on source: bacterial phospholipases can lyse host cells => Fe
phospholipase activity therefore often induced by low Fe

dietary iron - becomes part of transferrin and lactoferrin
ferritin intracellularly
proteins including hemoproteins

siderophores

52
Q

why is Fe important to bacterial function?

A

required for generation of ATP via electron transport chain

one of the defenses of host cells is to fenestrate Fe away from bacterial invaders

53
Q

what are siderophores?

A

have very high affinity for Fe
make Fe available to bacteria, often via specific receptors on the bacterial cell surface

secreted by bacteria - bind Fe that’s bound to protein and “steals” it since it has such a high affinity - brings it back to the bacteria

54
Q

what does it mean for an organism to be fastidious?

A

require growth factors to grow - such as purines, pyramidines, vitamins and several AA

55
Q

what does it mean for an organism to be prototrophic?

A

can usually synthesize everything it needs to grow - these can usually live outside of the host

56
Q

what is the advantage of agar medium (over liquid)?

A

allows observation of colony morphology
quantification
can separate out different types of bacteria

57
Q

why do we count bacteria?

A

knowing size of bacterial population allows you to determine if there’s an infection
antibiotic susceptibility testing needs to be done with cultures of a known density

58
Q

how do we count bacteria?

A

using a spectrometer - optical density = determined by the amount of light absorbed by a suspension of bacteria
amount of light absorbed by a cell suspension is measured by a spectrophotometer

dyes that indicate ECT activity

count cells under microscope - need a lot of bacteria though

plate counts - count number of colonies (CFUs = colony forming units)

59
Q

at what point can you see bacteria in culture?

A

get faint turbidity at 1 x 10^6

very turbid cultures will have 1 x 10^8 - 1 x 10^8 bacteria/mL

60
Q

what is the procedure to count CFUs?

A

1: make dilutions of the sample
2: plate these dilutions on a nutrient medium (agar)
3: incubate the plate overnight
4: count the number of colonies that grow up (30-300 colonies per plate is optimal)
5: calculate the number of viable cells (CFUs) that were in each mL of the undiluted sample

Micro Quiz 1 (9 decks)

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