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Microbial Growth - Coggle Diagram
Microbial Growth
Bacterial Population Growth
N=Nox2^(t/g)
N= final # of bact
No=initial #
t = total time
g= generation time
Lag = adjustment, no growth
Log = rapid cell division
Stationary= nutrients deplete, waste accumulates
Death = cell death > cell division
Oxygen Relationships
Obligate Anaerobes
: killed by O2
Facultative Anaerobes:
grow w/wo O2
Microaerophiles
: need small O2 amounts
Aerotolerant Anaerobes
: tolerate O2 but dont use it
Grown using
: Anaerobic chambers, CO2-rich culture chambers
Obligate Aerobes
: Need O2
Biofilms
Definition
: structured communities of microbes attached surfaces
Planktonic vs. Biofilm
: Planktonic (free-floating, indepen, more anti-biotic sensitive), Biofilm (attached, coordinated, resistant)
Quorum Sensing
: cell-to-cell chemical communication, coordinates group behavior
Functions
: 70% human infections involve biofilms, found on (catheters, heart valves, joints, lenses, teeth), Share nutrients & exchange plasmids/DNA, Protect (immune systems, drying, antibiotics)
Prevention
: antimicrobial surfaces, block quorom-sensing signals, lactoferrin binds iron and prevents motility, Pseudomonads are responsible for cystic fibrosis biofilms formation
Definitions and Basics
Microbial Growth= increase in # of sells, not size
Leads to formation of a colony
Reproduce by binary fission
Used to calculate generation time
Measuring Microbial Growth
Direct Serial Dilution & Viable Plate Count:
Most common method, Counts only live cells (CFUs), takes 24-48hrs,
pour plate vs spread plate
methods
Direct Microscopic Count
: Petroff-Hauser chambers, quick, inexpensive, counts live & dead cells, requires high bacterial concentration
Indirect Turbidity Measurement (Spectrophotometer)
: Measures light absorbance to est. population size, indirect, fast, requires 10-100 million cells to detect turbidity
Requirements for Microbial Growth
Physical Requirements
Temp
(Psychro (cold), Meso (mod), Thermo (hot) Danger (food 40-140)
pH
(Bacteria: 6.5-7.5), (Fungi: 5-6 acidic food), Biffers maintain pH (phos salts, peptones, AA)
Osmotic Pressure
(High Salt - inhibits microbes), (Halophiles grown in high salt [staphylococcus aureus)
Chemical Requirements
Carbon
: backbone of carbs, lipids, proteins, nucleic acids. (Heterotrophs: Organic C)(Autotrophs: CO2)
Nitrogen
: amino acids, nucleic acids
Sulfur
: some amino acids, use SO4^-2, or H2S
Phosphorus
: nucleic acids, ATP, PO4^-3 source
Trace elements
: enzyme cofactors
Organic Growth Factors
: vitamins, amino acids, purines, pyrimidines
Microbial Growth & Foodborne Illness
Staphylococcal Food Poisoning
Staphylococcus aureus (skin, nasal passages), Halophilic (grow in salty foods), Heat tolerant, enterotoxin survives boiling, temperature abuse (food left out), Symptoms last ~24hrs
Bacillus Cereus Gastroenteritis
Gram (+), spore-forming rod in soil, spores survive heating (germinates as food cools), releases extoxin (Nausea/Vomit 2-5hrs), (Diarrhea 8-16hrs)
Lab Culture Techniques
Streak Plate Method: obtains isolated colonies)
Preserving Cultures: Short-term (refrigeration), Long-term (Deep freeze -50C to -95C), (Lyophilization (freeze-drying -54C to -72C)