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MICR > L14 > Flashcards

L14 Flashcards

1
Q

three domains of life

A

Bacteria : prokaryotes
Archaea : prokaryotes
Eukarya : eukaryotes

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2
Q

Members of domain Bacteria are usually

A
  • Single celled
  • Cell walls with peptidoglycan
  • Typical prokaryotic structure
  • No membrane bound nucleus or organelles
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3
Q

Largest bacterium?

A

Thiomargarita namibiensis 100-300 μm, occasionally 750 μm – size of a full stop

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4
Q

Smallest bacterium?

A
  • Mycoplasma 0.3 μm diameter, cultivated
  • Ultrasmall uncultivated cells 0.009 μm (9 nm)
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5
Q

bacterium of average size

A

E.coli

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6
Q

New “largest bacterium” discovered in 2022

A
  • Thiomargarita magnifica grows up to 1 cm long!
  • found in Caribbean mangrove swamps
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7
Q

The two most common shapes of bacteria are:

A

1) coccus (plural cocci) (circular) -chains, clusters, pairs
2) and rod (also know as bacillus/ plural bacilli) -chains

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8
Q

Other bacterial shapes include:

A
  • Filamentous
  • Rigid spirals
  • Comma shaped rods
  • pleiomorphic
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9
Q

what are the 3 layers of a bacteria wall

A
  • Capsule
  • Cell wall
  • Plasma membrane

Out - in

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10
Q

What structures do all bacteria have

A
  • Cell wall (mostly)
  • Plasma membrane
  • Ribosomes
  • Nucleoid
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11
Q

What structures do some bacteria have

A
  • Capsules and slimes layers
  • Fimbrae and pili
  • Flagella
  • Endospores
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12
Q

Cell wall

A

nearly all
Provides cell shape and protection

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13
Q

Plasma membrane

A

all
Selectively permeable barrier,
boundary of cell, nutrient and waste transport, respiration

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14
Q

Ribosomes

A

All
Protein synthesis

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15
Q

Nucleoid

A

all
Location of DNA, single chromosome

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16
Q

Capsules and slime layers

A

some
Resistance to phagocytosis, adherence to surfaces

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17
Q

Fimbriae and pili
(singular: fimbria, pilus)

A

some
Adherence to surfaces, DNA transfer, twitching and gliding motility

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18
Q

Flagella
(singular: flagellum)

A

some
Swimming and swarming motility

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19
Q

Endospore

A

some
Survival under harsh condition

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20
Q

Gram positive bacteria stain

A

Purple

thick peptidoglycan

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21
Q

Gram negative bacteria stain

A

pink or red

thin peptidoglycan

22
Q

Gram positive cell envelope

A

▪ Cell wall
➢ thick, multi-layered peptidoglycan: a polymer of sugar chains cross-linked with peptides
➢ teichoic acids
▪ Plasma membrane
➢ phospholipid bilayer
➢ proteins

23
Q

Gram negative cell envelope

A

Cell envelope comprises:
▪ Cell wall = thin peptidoglycan layer
▪ Large periplasmic space between outer and inner membranes
▪ Outer membrane containing lipopolysaccharides (LPS)
▪ Plasma membrane

24
Q

Flagella

A
  • slender, rigid, helical proteinaceous structures extending from the plasma membrane and cell wall
  • mediate swimming bacterial motility: flagella rotate to propel the bacteria forward
25
Q

Flagella can be arranged as

A

▪ polar flagella – at one or both ends of a cell
▪ peritrichous flagella – spread over the whole surface of a cell

26
Q

Info

Pili and fimbriae

A

▪ short, fine, hair-like proteinaceous structures extending from the plasma membrane and cell wall
▪ thinner, straighter than flagella
▪ may be up to 1000 per cell
▪ many mediate attachment of bacteria to surfaces including host cells

27
Q

Two types of pili

A
  • sex pili, mediate transfer of DNA from cell to cell
  • type IV pili, mediate twitching motility by extending and retracting to pull the cell forward
28
Q

Bacterial endospores

A
  • extremely heat- and chemical-resistant, radiation-resistant, dormant, thick-walled spores that develop within the vegetative (mother) cells of some species
  • Don’t grow/ metabolise
  • Confer resistence for survival
  • Remain viable for 100000 years
  • pathogens Bacillus and Clostridium produce endospores
29
Q

binary fission

A
  • Young
  • Parent prep division by enlarging cell wall
  • Septum begins chromo move to opposite ends
  • Septum synthesised through centre
  • Daughters divided
30
Q

The significance of bacterial growth

A

▪ As a result of binary fission, populations increase in number. This increase is logarithmic or exponential: the number doubles at each generation. The generation time (g) is the time for a cell to produce 2 cells or the time for a bacterial population to double in number
▪ For E. coli g = 20 mins under optimal conditions
▪ for Mycobacterium tuberculosis g = ~ 12 hours

31
Q

as the number of bacteria increases in any one environment:

Why there is not continuous exponential growth

A
  • nutrients are used up
  • metabolic wastes accumulate
  • living space may become limited
  • aerobes may suffer from oxygen depletion
    Thus bacterial growth stops
32
Q

The bacterial growth curve

A
  1. Lag phase: synthesis of new components, cells preparing to divide
  2. Log or exponential phase: growth at maximal growth rate possible
  3. Stationary phase: total # viable bacteria constant, balance between cell division and cell death, nutrient or O2 limitation, or accumulation of toxic by-products
  4. **Death phase: **number of viable cells declines
33
Q

Influences of environmental factors on growth

Oxygen

A
  1. Obligate aerobe: Depend on O2 for growth; gain energy by aerobic respiration
  2. Microaerophile: Require 2-10% O2 Lower than atmospheric (~20%)
  3. Facultative anaerobe: Do not require O2 but grow better in its presence
  4. Aerotolerant anaerobe: Grow equally well in presence or absence of O2
  5. Obligate anaerobe: Killed by O2; Some gain energy by fermenting sugars
34
Q

Influences of environmental factors on bacterial growth

Temperature

Group, min temp, optimum temp, max temp, human strains?

A
  1. Mesophile(mod):10-15, 20-45, 45, Yes
  2. Psychrophile(cold-loving): -5, 15, 20, No
  3. Thermophile (heat-loving): 40, 60, 80, No
  4. Hyperthermophile: 65, 85-100, 113 (121?), No

Meso e.g: Escherichia coli. Hyperthermophile: hydrothermal vents ocean

35
Q

Almost all human pathogens are mesophiles, as human body is at constant (what temp)?

A

37oC

36
Q

Influences of environmental factors on bacterial growth

pH

optimum, human path

A
  • Acidphile: 0-5.5| yes
  • Neurtophile: 5.5-8|yes
  • Alkaliphile/alkalophile: 8-11.5| yes
37
Q

Most human pathogens are ________, but there are some important exceptions

Acidphile, Neutrophiles, Alkaliphile/alkalophile

A

Neutrophiles

38
Q

Culture Media: The design of culture media for bacteria is determined by:

A
  1. sources of carbon, electrons and external energy used for growth
  2. the diversity of chemicals needed to make bacterial cell components
  3. the need for growth factors (e.g. vitamins, amino acids)
39
Q

Culture Media: two common methods

A
  1. Liquid culture: Bacteria grown as a liquid suspension (‘broth culture’)
  2. Solid culture: Bacteria grown on an agar (gel) surface (‘plate culture’)
40
Q

Colony appearance on solid media helps microbiologists to identify bacteria, as species often form colonies of characteristic size and appearance
* each colony arises from a single cell and represents a pure culture

A
41
Q

Features of Culture Media

A
  1. Complex media
  2. Selective media
  3. Differential media
42
Q

Complex media

A

▪ contain some ingredients of unknown chemical composition
▪ may include peptones, meat extract, yeast extract, blood
▪ useful as many bacteria can grow on them
▪ some common media include:
* nutrient broth, nutrient agar, tryptic soy broth and agar, blood agar, MacConkey agar

43
Q

Selective media

A

▪ allow the growth of some bacteria while inhibiting others

44
Q

Differential media

A

▪ distinguish between different bacteria and may allow tentative identification

pH change in agar

45
Q

MacConkey agar culture media?

A

MacConkey agar is both selective and differential

46
Q

MacConkey agar features

A

*Bile salts and crystal violet inhibit Gram positive bacteria but not Gram negative bacteria
*Lactose and neutral red, a pH indicator, differentiate lactose fermenters (pink) from non-fermenters (colourless)

47
Q

Taxonomic ranks

A

Groups at any rank level share common properties with the group they belong to in the rank above

48
Q

Taxonomy

A

is the science of classifying living things

49
Q

Species:

A

collection of strains that share many stable properties and differ from other groups of strains

50
Q

Strain:

A

population derived from a single cell; descendants of a single, pure microbial culture. Strains differ only slightly from one another e.g. antibiotic R or S, or different serotypes

MICR (18 decks)

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