Microbiology: Chapter 6 Microbial Growth Flashcards
College: Third year
Physical Requirement
-temperature
-pH
-osmotic pressure
Psychrophiles
- a cold-loving microbe
- an organism that grows best at about 15oC & does not grow above 20oC
Psychrotrophs
an organism that is capable of growth between about 0oC & 30oC
Mesophiles
- a moderate-temperature-loving microbe
- an organism that grows between about 10oC & 50oC
Thermophiles
- a heat loving microbe
- an organism whose optimum growth temperature is between 50oC & 60oC
Hyperthermophiles
- an organism whose optimum growth temperature is at least 80oC
- also called extreme thermophile
pH
- minimum, optimum, maximum
* most bacteria: optimum= 6.5-7.5
* molds and yeasts: optimum= 5-6
* human pathogens: optimum= 7.4 (pH of blood)
pH
- acidophiles: acid-tolerant microbes
* stomach pH: 1 (Helicobacter pylori)
* vagina pH: 3-5 (Lactobacillus)
- acids from fermentation preserve foods
- microbial wastes are acidic
* use buffers in media
Hypotonic (Osmotic Pressure)
- a solution that has a lower concentration of solutes than an isotonic solution
- water moves inside the cell & the cell will lyse
- gram-negative bacteria are more susceptible to this
- most microbes is in this type of environment
Hypertonic (Osmotic Pressure)
- a solution that has a higher concentration of solutes than an isotonic solution
- water moves out the cell & the cell shrink
- extreme & facultative halophiles
Chemical Requirements
- energy
- carbon
- hydrogen
- nitrogen
- oxygen
- phosphorus
- sulfur
- trace elements
- organic factors
Carbon
- 50% of dry weight of a typical bacterial cell
- obtain through energy sources (carbs,lipids,proteins) or CO2
- autotroph: CO2 is carbon source
- heterotroph: organics as carbon source
Nitrogen
needed for protein, nucleic acid & ATP synthesis
Sulfur (S)
needed for protein (in Cys & Met) & vitamin synthesis (Biotin & thiamine)
Phosphorous (P)
- DNA & RNA
- phosopholipids
- ATP
Cofactors and Trace Elements
- potassium, magnesium, calcium
- trace elements: iron, copper, molybdenum, zinc
- organic molecules obtained from the environment
Oxygen
- molecular oxygen (o2) yields toxic products
- aerobes require O2 for aerobic respiration
- anaerobes don't use O2 for energy production
- anaerobic respiration & fermentation
Oxygen Toxicity
- radicals are formed
* when cells grow in O2 environment
* ionizing radiation
- O2 -: superoxide OH-: hydroxyl ion H2O2: hydrogen peroxide O2 2-: peroxide ion
- unstable; disrupt electron arrangements around other molecules > DNA or cell damage
Detoxification
- naturally occurring antioxidants
* tocopherol (vitamin E)
* ascorbic acid (vitamin C)
* melatonin
- detoxifying enzymes
* superoxide dismutase
* catalase
* peroxidase
Detoxifying Enzymes
- superoxide dismutase (SOD)
O 2 - + O2 - + 2H+ > H2O2 + O2
- catalase
2H2O2 > 2H2O + O2
-Peroxidase
H2O2 + 2H + > 2H2O
Thioglycollate
- reducing medium
- take the oxygen & reduce it into water O2 > H2O
Obligate Aerobes
organisms that require oxygen to live
Facultative Anaerobes
an organism that can grow with or without oxygen
Obligate Anaerobes
organisms that does not use oxygen to live & is killed in the presence of oxygen
Aerotolerant Anaerobes
an organism that does not use oxygen to live but is not affected by its presence
Microaerophiles
an organism that grows best in an environment with less oxygen than is normally found in air
Biofilms
- bacteria are usually found in communities
* rarely as isolated species
- matrix of polysaccharide, DNA & proteins
- quorum sensing
* communication via chemical cues
Biofilms
- benefits
* share nutrients
* shelter
* increase opportunity for genetic exchange
* cooperative activity
Biofilms
- impact human health
* 70% of human infections involve biofilms
~ responsible for most nosocomial disease
* form on catheters & medical devices
* more resistant to antimicrobial agents
Culture Media & Techniques
- medium: nutrient preparation used to grow microbes
* H2O, carbon, required elements, O2 (if needed)
* correct pH and temp
* broth vs agar
*steril
- chemically defined vs. complex medium
selective & differential medium
- anaerobic growth
- special culture techniques
* selective & differential medium
Selective Media
- supports growth of specific organisms while inhibiting others
- eosin methylene blue (EMB)
* selects for gram-negative
~ enterobacteria- enteric/gut bacteria
~ facultative anaerobes
* dyes inhibit growth for gram-positive
Phenylethyl Alcohol (PEA) Agar
- selects for gram-positive species
- little/no growth of gram-negative
Mannitol Salt Agar
- selects for facultative halophiles (7.5% salt)
- staphylococcus
Sabouraud's Agar
selects for fungi (pH 5.6)
Differential Media
- distinguishes between microbes based on identifiable reactions with the medium
Blood Agar
- differential media
- contains 5% sheep's blood
- hemolysins: exotoxins that destroy RBCs
* alpha-hemolysis > partial lysis
* beta-hemolysis > total lysis
* gamma-hemolysis > no lysis
Alpha-Hemolysis
- greenish-brown halo
- Streptococcus pneumoniae
Beta-Hemolysis
- clear halo around colonies
- Streptococcus pyogenes
- Staphylococcus aureus
Gamma-Hemolysis
most bacteria
Eosin Methylene Blue (EMB) Agar
- selects for gram-negative species
- differentiates between lactose/sucrose fermenters and non-fermenters
Mannitol Salt Agar
- selects for Staphylococcus (high salt 7.5%)
- differentiates between mannitol fermenters and non-fermenters
Anaerobic Growth
-reducing media
* contains ingredients that deplete O2
* example: Thioglycollate medium (liquid)
- anaerobic jars
* used for plate cultures
* colony growth
- anaerobic chamber
Special Culture Techniques
- animals
* some microbes don't grow on artificial media
* Mycobacterium leprae
~ mouse foot pads and armadillos (low temp)
* Treponema pallidum
~ rabbit testes
Special Culture Techniques
- cell culture (intracellular bacteria: example: Chlamydia)
- growth of capnophiles
* require elevated CO2 but are aerobic
~ intestines, respiratory tract, body tissues
* CO2 incubator
* candle jar
Bacterial Growth
- most reproduce by binary fission
- budding
* outgrowth of cell that grows and separates from parent
Bacterial Growth
- external spores (conidiospores)
* filamentous bacteria
* spores develop into new cells
* more common for fungi
-fragmentation
* new cells grow from fragments
Generation Time
- time required for cell number to double
- factors affecting generation time
* species of microbe
* environmental: temp, pH, nutrients, type of media
Logarithmic Growth
- exponential growth
- cell # increases by a constant factor for each unit of time
- Log: the power to which a base number is raised to produce a given number (Log101=10 & Log106=1000000)
* bacterial growth is linear on log graph
Lag Phase (Phases of Growth)
little or no change in the number of cells, but metabolic activity is high
Log Phase or Exponential Growth (Phases of Growth)
bacteria multiply at the fastest rate possible under the condition provided
Stationary Phase (Phases of Growth)
there is an equilibrium between cell division & death
Death Phase or Logarithmic Decline (Phases of Growth)
the number of deaths exceeds the number of new cells formed
Measurement of Growth
- population numbers (cells/ml or cells/g)
- direct measurement
- indirect measurement
Direct Measurement
- technique that involves some counting
- count small sample & determine total population
Indirect Measurement
- estimation of cell numbers without counting cells
- turbidity, mass, spectrophotometry
Plate Count
- most frequently used
- advantage: measures only living cells
- disadvantage: takes time
- cell vs colony forming unit
* colony can form from 1 cell or a clump of cells
* plate counts are in CFU/mL
- serial dilutions to get good # colonies/plates
* 30-300 CFU/mL
- pour plate
- spread plate
Filtration Method
- volume passed through membrane (bacteria trapped)
- transfer to plate & grow
- count colonies & divide by number of mL filtered (CFU/mL)
- good when bacteria # is small
* can't count 1 CFU/mL
*example: water samples (coliform bacteria)
Direct Microscopic Count
- count number of cells spread over grid using a microscope
- average # microbes in several squares
- average X conversion factor X dilution factor
- advantages: quick (no incubation required) & counts all cells (live & dead)
- disadvantage: difficult to count motile bacteria
Turbidity
- indirect
- uses spectrophotometer
* measures amount of light passing through a sample
* % transmittance
* absorbance
- # cells is directly proportional to turbidity of culture
* increase # cells/ml (turbidity), increase absorbance
- advantage: quick & easy
- disadvantages: must be read during log phase & needs to be correlated to direct measurement