Microbiology 2 Flashcards
1
Q
why should we control Bacterial cell cycle
A
- Infectious disease caused by bacteria
- Food spoilage
- Pharmaceutical spoilage
- Environmental microbial contamination
2
Q
Bacterial cell cycle (binary fission)
A
- 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
3
Q
Stages of bacterial cell growth
Lag phase
A
- 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
4
Q
Stages of bacterial cell growth
Log phase
A
- Logarithmic or exponential increase in population
- Rapid and constant population growth (exponential manner)
- Number of cells produced > Number of cells dying
5
Q
Stages of bacterial cell growth
Stationary phase
A
- Period of equalibrium microbial deaths balance production of new cells
- Population size begins to stabilize
- Number of cells produced = Number of cells dying
6
Q
Stages of bacterial cell growth
Death phase
A
- Population is decreasing at a logarithmic rate
- Number of cells produced < Number of cells dying
7
Q
Generation time
A
- Time required for a bacteria to complete the cell cycle
- Binary fission doubles the number of cells each
generation
8
Q
Biofilms
A
- 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
9
Q
physical requirements for bacterial growth
A
- Temperature
- pH
- Osmotic pressure
10
Q
Chemical requirement for bacteria growth
A
- Carbon source
- Ions and trace elements
- Oxygen nitrogen sulpher and phosphates
- Organic growth factors
11
Q
Temperature for optimum growth of Psychrophiles
A
Cold loving at the temperature < 15 degrees
12
Q
Temperature for optimum growth for Psychrotrophs
A
- 20 to 30 degrees is the optimum temperature
13
Q
Mesophiles optimum temperature
A
- between 25-30 degrees division of bacteria
14
Q
Thermophiles
A
Heat loving at like 50-60 degrees
15
Q
Temperatures effect on storing medicines
A
- 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
16
Q
pH and inhibiting microbial growth
A
- Low pH cause a decrease in microbial growth
- Alkali not usually used for preservation
17
Q
Osmotic requirements for bacteria
A
- Simlar requires isotonic and hypertonic could cause plasmolysis due to high osmotic pressure
- Halophiles tolerate high osmotic pressure
18
Q
element requirement for microbial growth
A
- 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
19
Q
Why are trace elements required
A
Fe, Cu, Zn in small amounts used as enzyme cofactorsf
20
Q
Obligate Aerobes
A
Require oxygen to live. E.g. Pseudomonas, causing
infections in humans, mostly in hospital patients
21
Q
Facultative anaerobes
A
- Can grow via fermentation or anaerobic
respiration when oxygen is not available. Grow best in aerobic conditions. E.g. E.coli
22
Q
Obligate anaerobes
A
do not tolerate oxygen and are harmed by it.
E.g. Clostridium bacteria that cause tetanus and botulism
23
Q
Culture
A
Microbes growing in/on culture medium
at appropriate conditions
24
Q
Culture medium
A
Nutrients prepared for microbial
growth in a laboratory
25
What must a bacterial culture have
Have to be sterile (not contain living microbes)
and contain nutrients and incubate
26
Inoculum
- Enables you to transfer microbes into a medium
27
Agar
- Complex polysaccharide (solid medium)
- Used as a solidifying agent for culture media in Petri plates
- Generally not metabolized by microbes
28
Selective media
- Suppress unwanted microbes and encourage desired microbes
- Saboraud's Agar - 5.6 pH discourages bacteria growth which is used to isolate fungi
29
Differential media
Allow distinguishing of colonies of different microbes on the same plate
| blood agar distingishes distinguishes bacteria and destroys red blood ce
30
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)
31
Pure culture
individual organisms must be isolated
- Streak-plate method is commonly used
- use aseptic techniquie to maintain sterile environment
32
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
33
Colony formation
A population of cells arising
from a single cell (colony forming unit)
34
Direct measures of microbial growth
- Plate count
* Filtration
* Direct microscopic count
35
Indirect measurements
- Turbidity (mass)
* Metabolic activity
* Cell mass - Dry weight
36
Counting colonies
- Ensure right number of colonies via serial dilutions from original inoculum
37
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
38
Number of bacteria
Number of cells counted/ volume of area counted
39
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.
40
Disadvantages of Direct microscopic count
- Difficult to distinguish live/dead bacteria
- Often laborious
- Only suitable with high counts
41
Turbidity/Cell mass
- Measurement of cloudiness/optical density (linked to the cell mass) of liquid media by a spectrophotometer
42
Metabolic activity
- Amount of metabolic product is proportional to the
population size
43
Cell mass / Dry Weight
- Bacteria are filtered, dried, and weighed; used for
filamentous organisms
