Microbial Growth Chapter 4
Objectives What are the factors that influence bacteria growth? Oxygen requirements Nutrient requirements Carbon, Nitrogen, Sulfur, Phosphorous Counting microogranisms
Microbial Growth Growth= an increase in the number of cells, not an increase in size Generation=growth by binary fission Generation time=time it takes for a cell to divide and the population to double
Bacteria divide by binary fission
Biofilms are communities of bacteria
Examples of Biofilms
Generation times vary for each organism E. coli 20 minutes (optimal conditions) Mycobacterium tuberculosis 24 hours 6 week incubation for clinical diagnosis
Bacterial growth curve Questions: Antibiotics would have the greatest impact on which phase? Why do microbes enter the stationary phase? At which phase(s) would spores be formed?
Primary and Secondary metabolites Metabolites are required for growth Metabolites are required for survival
Requirements for bacterial growth Environmental factors that influence Temperature, pH, osmotic pressure, oxygen Nutritional factors Carbon, nitrogen, sulfur, and phosphorous Trace elements
Optimum Growth Temperatures Psychrophiles- optimum -5 to 15oC Psychrotrophs- range from 20-30oC Mesophiles- range from 25-45oC Thermophiles- range from 45-70oC
pH influences the growth Bacteria-prefer a pH range of 6.5-7.5 Molds prefer a pH range of 5.0-6.0
Osmotic environment influences growth
Oxygen preferences of organisms Obligate aerobes Facultative anaerobes Obligate anaerobes
Why can some organisms grow in the presence of oxygen? Reactive Oxygen Species are byproducts of Aerobic Respiration They are extremely toxic to both Prokaryotic and Eukaryotic cells DNA Damage Oxidize Amino Acids Inactivate Enzymes Disrupt Membranes Activate Immune System
Why can some organisms grow in the presence of oxygen? Toxic forms of oxygen need to be neutralized by enzymes Superoxide dismutase Accepts electrons to make H2O2 Catalase Converts to 4H2O2 to 2H2O + 2O2 Peroxidase
Oxygen Preferences of Bacteria
Candle jars increase CO2 levels for growing capnophiles
Anaerobic jars eliminate the oxygen for anaerobes to grow.
Chemical requirements: Carbon What are possible sources of carbon? Bacteria are classified based on the source of carbon as either heterotrophs or autotrophs Heterotrophs take carbon from the environment (consumes), Autotrophs use carbon from carbon dioxide
Classification based on Energy and Carbon sources
Chemical Requirements: Nitrogen Why do bacteria need nitrogen? Component of Amino Acids and Nucleic Acids
Chemical requirements: Sulfur and Phosphorous Why do bacteria need sulfur? Why do bacteria need phosphorous? Sulfur is a component of some Amino Acids, Phosphorous is a component of ATP, nucleic acids, membrane lipids.
Chemical requirements: trace elements Small amounts of minerals Cobalt, zinc, copper, manganese, etc. Usually function as cofactors
Culture Media Chemically defined GSA GSA – Glucose Salt Agar
Chemically defined media
Culture Media Complex Nutrient Agar TSA BHI TSA – Trypticase Soy Agar, BHI – Brain/Heart Infusion Media
Culture Media Selective Differential Selective and Differential Blood EMB EMB – Eosin Methyl Blue, Chocolate – lysed blood media
Ways to measure bacterial growth Direct Count Plate Count/Viable Cell Count Measure Turbidity
Direct Counts
Plate counts require dilutions
Two techniques for plate counts
Turbidity gives a rough estimate
Standard Curves You may determine the precise concentration of suspension by running knowns amounts and extrapolating data Normalized absorbance Concentration, mg