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Microbial Growth - Coggle Diagram
Microbial Growth
Defining Microbial Grown and reproduction
Increase in umber of cells, not cell size
On solid media-forms a colony
on solid media-forms a colony
colony= group of same organisms attached in clumps or chains
reproduction method-binary fission
bianry fission-time required of a cell to divide
generation time: 1-3 hours
Bacterial population
N=N0 x 2^(t/g)
N=final number of bacteria
t= total time(hours)
g= generation time(hours)
requirements for microbial growth
physical requirements
Temperature
pH
Osmotic Pressure
Chemical Requirements
Carbon
Nitrogen
Sulfur
Phosphorus
Ocygen sources
Trace elements
Organic growth factors
Physical Requirements Details
Most bacteria grow best at neutral pH(6.5-7.5)
Fungi prefer acidic (pH 5-6)
Buffers (phosphate salts, peptones) resist pH change
temperature abuse (41F-125F or 5C-57C)-rapid growth
Staphylococcus aureus
ssalt-tolerant(7.5%)
Grows in high osmostic pressure (e.g., ham, potato salad)
produces enterotoxin (survives boiling 30 min)
Bacillus cereus
laarge Gram-postiive bacillus
Forms spores (resistant to heat)
spores germinate as the food cools
Chemical Requirements Detaisl
Carbon: Backbone of organic compounds
Heterotroph-gets carbon from orgainc sources
Autotroph-get carbon from CO2
Nitrogen-needed for amino acids & nuceic acids
Phosphorus-found in nucleic acids
Biofilms and Communication
Planktonic vs biofilm
Planktonic bacteria-free-floating, easier to kill
Bioflim-structured community attached to surfaces
Communication
qourum sensing-chemical signaling between cells
Biofilm facts
Cause- 70% of human bacterial infections
Protect microbes from:
Environment
Desiccation
Immune defenses
Lsctoferrin-prevents biofilms formation by binding iron
Measuring and preserving microbial growth
Presevation
Lyophilication(freeze-drying)- long-term storage
Deep freezing-long-term storage
Refrigeration- short-term (sows replication)
measurement methods
Serial dilution-most common for population counts
Viable plate count- counts living cels (1 colony= 1 CFU), takes 24-72 hrs
Direct microscopic count- fast, counts live + dead cells, needs many bacteria
Spectrophotometry- measures turbidity