Chapter 4 Flashcards
What is Asexual Reproduction called
Binary Fission
Microbial Growth
The growth of a population through an increase in the number of cells in a specific amount of time
Binary Fission steps
- Parent cell increases in size
- Chromosome is copied
- DNA attaches to cell membrane
- New cell walls form
- Cell divides into two new cells
Budding
Yeast and some bacteria species
a bud forms on parent cell
Growth curve
Distinct, sequential phases of growth in a lab with a closed system (agar, broth)
Steps of Growth Curve
- Lag Phase
- Exponential (Log) phase
- Stationary Phase
- Death phase
Lag Phase
- preparation for cell division; no increase in population size
Metabolic Activity
-Enzyme and protein synthesis
-Breakdown of substances in environment
-Synthesis of new macromolecules and ribosomes
How long is lag phase?
Varies because of bacteria type and environment
Exponential (Log) Phase
- Cell numbers increase exponentially (slowly at first then extremely rapid)
- Cells are most virulent at this phase
- Most sensitive to antimicrobial medications
- Limited by nutrients, oxygen, waste accumulation, space
Generation time
Time it takes for one cell to divide into two cells (or population to double).
-10 minutes to 24 hours (average 30 minutes)
Formula for measuring population
Nt = N0 x 2n N0= original number of cells in a population Nt= number of cells in a population at a given time n= number of divisions in a given amount of time
Stationary Phase
Environmental conditions do not favor continues growth
-Death rate = division rate
Cells may produce survival structures (glycocalyx, endospores, cytoplasmic inclusions
Abcess
collection of pus surrounded by inflamed tissue
What is pus made of
WBCs, tissue debris, prtoeins and bacteria
Abscess
why formed and what happens
Body’s response to bacteria
Nutrients are limited so bacteria go to stationary phase
Are antimicrobials effective for abscesses?
No because bacteria is not dividing
Death phase
Cells begin to die out
Exponential death at a low rate
ATP reserves depleted
Prolonged decay: some cells survive by using nutrients of dead cells
Growth Phases in lab vs. nature
-Cultures pass through all growth phases in lab but not in nature.
- In nature nutrients enter cell’s environment at low concentrations.
therefore growth is continuous, steady but at a low rate. Limited by nutrients. Metabolic wastes are removed by other microbes
Nutrients r/t position in colony
growth on agar
Edges: lots of nutrients = exponential growth
Middle: limited nutrients = stationary growth
Center: depleted nutrients = death
Growth on agar
On solid media bacteria grows in colonies
Colony
a distinct mass of cells that originate from a single cell
Microbes can exist in many environments because they are…
small
easily dispersed
need only small quantities of nutrients
diverse in nutritional requirements
Environmental influences on Microbial Growth
moisture, temperature, pH, oxygen, solute concentration, hydrostatic pressure, radiation, nutrients
Moisture
influences on microbial growth
- Bacteria use diffusion to get nutrients from the environment (so water is needed for diffusion to occur)
- Preserving food through dehydration prevents bacteria from multiplying but may not kill bacteria
Temperature
influences on microbial growth
-Microbial species have specific temperature ranges in which they can grow
Reasons why extreme heat or cold affects growth
very cold - proteins not denatures, microbes not killed just slowed
very hot - proteins denatured, metabolism stops, cells destroyed
Optimum temperature
Usually a small range where organism has fastest rate of growth
Psychrophiles
cold loving
5-15 C
Grow in polar and glacial regions
Psychrotrophs
“cold feeding”
20 - 30 C
do not cause infection in humans
responsible for spoiling of refrigerated and frozen food (Blood)
Mesophiles
middle loving
25 - 45 C
Pathogens are mesophiles
optimum temperature for human pathogens is around 37C
Normal body temp in C
37 C
Most refrigerators run what temp in C
4 C
Thermophiles
heat loving
45 - 70 C
Found in natural hot springs, compost
Hyperthermophiles
extreme heat loving
70 C and higher
usually Archaea
hydrothermal vents in ocean
pH
influences on microbial growth
pH of external environment - internal pH is neutral
Acidophiles
optimal pH is below 5.5
example: H. Pylori
Neutrophiles
optimal pH 6-8
Human pathogenic bacteria optimum pH is 7.3
Alkaliphiles
optimal pH above 8.5 (very small group of bacteria
ex. alkaline lakes and soils
Bleach
pH of 10
kills most bacteria
Hydrostatic pressure (influences on microbial growth)
- pressure exerted by standing water
- Most bacteria killed by high pressure (autoclave)
- Some extreme microbes need high pressure to keep enzymes from denaturing
Radiation
influences on microbial growth
Can damage or kill microbes
3 types: Ionizing, UV, microwave
Ionizing radiation
removes electrons - destroys DNA, damages membranes
ex. Xrays and Gamma rays
Gram + can survive longer than Gram -
Uv radiation
destroys DNA (mutations) some bacteria have repair enzymes to correct mutations
Microwave radiation
kills bacteria with heat only
Harmful oxygen-containing molecules
Superoxide ion (o2-)
Peroxides(H2O2)
Damage living tissue (especially membranes and can kill cells -> aging
Antioxidants
Enzymes present in organisms to detoxify harmful oxygen containing molecules
Examples of antioxidants
Superoxide dismutase (SOD) Catalase
Superoxide dismutase
converts O2- to O2 + H2O2
Catalase
converts H2O2to O2 and H2O
Obligate Aerobes
- Have SOD and catalase
- must have O2 for metabolism (aerobic respiration) and growth
- ex. most fungi and protists, some bacteria (Bacillus, Pseudomonas)
Facultative Anaerobes
- Usually have SOD and catalase
- “flexible” - can survive with or without oxygen
- Grow best with oxygen (aerobic respiration
- Ex. Ecoli, Staphylococcus and Saccharomyces(yeast)
Microaerophiles
- Only need small amounts of SOD and catalase
- Need small concentrations of O2( 2-10%) for aerobic respiration
- Large amounts of oxygen are inhibitory
- Found in mucous linings of hollow organs
- Ex. H. Pylori
Obligate Anaerobes
- Usually lack both SOD and catalase
- Cannot grown if O2 is present
- No aerobic respiration
- Found in deep mud, lakes, oceans, inside animal bodies
- Ex. Clostridium
Aerotolerant Anaerobes
- May have SOD, but not catalase
- Indifferent to oxygen
- Do not use oxygen (OBLIGATE FERMENTERS)
- Ex. Streptococcus pyogenes
How do bacteria try to maintain a hypotonic environment?
They will pump in K+ of produce extra amino acids
Halotolerant
- can tolerate moderate concentrations of salt - up to 10% NaCl
ex. staph on the skin
Halophiles
- REQUIRE a high level of NaCl
- Marine microbes
- Extreme halophiles are Archaea living salt lakes
Osmophiles
grow in high sugar concentrations
Element reminds
C. Hopkins CaFe Mg
C. Hopkins Cafe Mighty good
Carbon
energy source (glucose) and building blocks
Nitrogen
amino acids, nucleotides
- some can synthesize all 20 amino acids
- others need amino acids added to culture medium
Sulfer
amino acids, coenzymes
Phosphorus
ATP, phospholipids, nucleotides
Vitamins
- organic substance required by an organism, usually a coenzyme
- some bacteria make own vitamins
- others need vitamins added to culture medium
- microbes in human intestine make Vitamin K and some B vitamins = mutualistic symbiosis
Other elements are often…
cofactors
Media
liquid or solid material used to grow microbes
Agar
solidifies culture media at 1.5% concentration
- complex polysaccharide, extracted from seaweed
- melts at 100C and solidifies at 45C
- first used by Koch (Mrs. Hess)
- not degraded by microbes
Sterilizing agar
in autoclave
121 C for at least 15 minutes at 15 psi of steam
Liquid Media (broth)
good for growing large numbers of bacteria in a short time, contains low concentrations of agar (0.5%) for motility test
Defined (synthetic) media
made of exact amounts of pure chemicals
Complex media
- made of some ingredients with variable chemical composition
- can vary from batch to batch
- extracts from beef, yeast, blood…
- example nutrient agar
Selective media
- encourages the growth of some microbes and suppresses the growth of others
- for isolation of microbes
Differential Media
- contains substances that certain microbes can change in a recognizable way
- observable changes in media due to biochemical reaction from microbe
- ex. color or pH change
Indirect measurements
measure property of the mass of cells and then estimate the number of microbes
Direct measurement
determine the total number of cells, includes living and/or dead cells, more accurate measurements of numbers of microbes
Turbidity
- cloudiness as evidence of growth
- can use spectrophotometer
- measures biomass not number of cells
- cannot detect minor concentrations
Metabolic Activity
- Rate of metabolic products that a culture produces: gases, acids
- Rate of utilization of a substrate: Oxygen, glucose, ATP
- Rate of reduction of certain dyes: methylene blue becomes colorless when reduced
2 types of Indirect measurement
Turbidity
Metabolic Activity
Direct cell counts
- Direct Microscope count
2. Coulter Counter
Direct microscope count
special glass slide with light compound microscope
Coulter Counter
- electronic, cells pass through a narrow channel
- rapid, accurate
Viable cell count
- Standard plate count
2. Filtration
Standard plate count
count colonies against a grid
- Quebec colony counter
- use serial dilutions to decrease cell numbers before counting
Filtration
viable cell count technique
fine, sterile filter collects microbes, then placed on agar plate, count colonies, used to concentrate samples
Countable plate has how many cells
30 -300
more - too many cells produce too many colonies to count
less - not enough colonies for a valid count
