Microbiology 2 Flashcards
why should we control Bacterial cell cycle
- Infectious disease caused by bacteria
- Food spoilage
- Pharmaceutical spoilage
- Environmental microbial contamination
Bacterial cell cycle (binary fission)
- Cells elongate and enlarge its volume and DNA replicates
- Cell wall and plasma membrane begin to constrict
- Cross-wall forms,completelyseparating the two DNA copies
- Cells seperate
Stages of bacterial cell growth
Lag phase
- Intense activity preperation of population growth but no increase in population
- Little or no cell division occurs
- Intense metabolic activity. Individual cells increase in size
Stages of bacterial cell growth
Log phase
- Logarithmic or exponential increase in population
- Rapid and constant population growth (exponential manner)
- Number of cells produced > Number of cells dying
Stages of bacterial cell growth
Stationary phase
- Period of equalibrium microbial deaths balance production of new cells
- Population size begins to stabilize
- Number of cells produced = Number of cells dying
Stages of bacterial cell growth
Death phase
- Population is decreasing at a logarithmic rate
- Number of cells produced < Number of cells dying
Generation time
- Time required for a bacteria to complete the cell cycle
- Binary fission doubles the number of cells each
generation
Biofilms
- Microbial communities
- Form slime or hydrogels that adhere to surfaces
- Bacteria communicate cell-to-cell
- Share nutrients
- Shelter bacteria from harmful environmental
factors or microbicides
physical requirements for bacterial growth
- Temperature
- pH
- Osmotic pressure
Chemical requirement for bacteria growth
- Carbon source
- Ions and trace elements
- Oxygen nitrogen sulpher and phosphates
- Organic growth factors
Temperature for optimum growth of Psychrophiles
Cold loving at the temperature < 15 degrees
Temperature for optimum growth for Psychrotrophs
- 20 to 30 degrees is the optimum temperature
Mesophiles optimum temperature
- between 25-30 degrees division of bacteria
Thermophiles
Heat loving at like 50-60 degrees
Temperatures effect on storing medicines
- 60 - 130 degrees Temperatures in this range destroy most microbes, although lower temperatures take more time
- 50-60 degrees very slow bacterial growth
- 15-50 danger zone rapid replication
- 5-15 many bacteria survive some may grow
- 0-5 refridgerator temp may slow growth and cause spoilage but few pathogen
- No significant growth below freezing
pH and inhibiting microbial growth
- Low pH cause a decrease in microbial growth
- Alkali not usually used for preservation
Osmotic requirements for bacteria
- Simlar requires isotonic and hypertonic could cause plasmolysis due to high osmotic pressure
- Halophiles tolerate high osmotic pressure
element requirement for microbial growth
- Carbon is a structural backbone of organic compounds
- Nitrogen forms amino acids DNA and RNA
- Sulfer for thiamin and biotin
- Phosphorous - for DNA RNA and ATP
Why are trace elements required
Fe, Cu, Zn in small amounts used as enzyme cofactorsf
Obligate Aerobes
Require oxygen to live. E.g. Pseudomonas, causing
infections in humans, mostly in hospital patients
Facultative anaerobes
- Can grow via fermentation or anaerobic
respiration when oxygen is not available. Grow best in aerobic conditions. E.g. E.coli
Obligate anaerobes
do not tolerate oxygen and are harmed by it.
E.g. Clostridium bacteria that cause tetanus and botulism
Culture
Microbes growing in/on culture medium
at appropriate conditions
Culture medium
Nutrients prepared for microbial
growth in a laboratory
What must a bacterial culture have
Have to be sterile (not contain living microbes)
and contain nutrients and incubate
Inoculum
- Enables you to transfer microbes into a medium
Agar
- Complex polysaccharide (solid medium)
- Used as a solidifying agent for culture media in Petri plates
- Generally not metabolized by microbes
Selective media
- Suppress unwanted microbes and encourage desired microbes
- Saboraud’s Agar - 5.6 pH discourages bacteria growth which is used to isolate fungi
Differential media
Allow distinguishing of colonies of different microbes on the same plate
blood agar distingishes distinguishes bacteria and destroys red blood ce
Enrichment Culture
Encourages the growth of a desired microbe by increasing very small numbers of a desired organisms to detectable levels (don’ t supress other microoganisms)
Pure culture
individual organisms must be isolated
- Streak-plate method is commonly used
- use aseptic techniquie to maintain sterile environment
Streaking technequie
- Loop is sterilized then inoculated
- First set of streaks are made on agar with nutrients
- Loop is resterilized
- Second set of streaks are made
- Loop is resterilized
- Final set of streaks are made
- Isolated colonies develop after incubation
Colony formation
A population of cells arising
from a single cell (colony forming unit)
Direct measures of microbial growth
- Plate count
- Filtration
- Direct microscopic count
Indirect measurements
- Turbidity (mass)
- Metabolic activity
- Cell mass - Dry weight
Counting colonies
- Ensure right number of colonies via serial dilutions from original inoculum
Membrane filteration
- Solution passed through a cellulose filter (0.45 μM) that collects and retains bacteria - (bacteria size > pore size)
- Filter applied to petri dish so it can grow on the surface
- Incubate for 24 hours then count
Number of bacteria
Number of cells counted/ volume of area counted
Direct microscope count
- Placing a small amount of samples on a microscope slide with a special grid
- Stain is added to visualize bacteria
- Cells are counted and multiplied by a factor to obtain concentration.
Disadvantages of Direct microscopic count
- Difficult to distinguish live/dead bacteria
- Often laborious
- Only suitable with high counts
Turbidity/Cell mass
- Measurement of cloudiness/optical density (linked to the cell mass) of liquid media by a spectrophotometer
Metabolic activity
- Amount of metabolic product is proportional to the
population size
Cell mass / Dry Weight
- Bacteria are filtered, dried, and weighed; used for
filamentous organisms
