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

Generation times vary for each organism E. coli Staphylococcus aureus Mycobacterium tuberculosis

Why is generation time important? Food? Infections

Bacterial growth curve

Primary and Secondary metabolites

Requirements for bacterial growth Environmental factors that influence –Temperature, pH, osmotic pressure, oxygen Nutritional factors –Carbon, nitrogen, sulfur, and phosphorous –Trace elements metals

Optimum Growth Temperatures Psychrophiles- –optimum -5 to 15 o C Psychrotrophs- –range from o C Mesophiles- –range from o C Thermophiles- –range from o C

pH influences the growth Bacteria-prefer a pH range of Molds prefer a pH range of

Osmotic environment influences growth Salt concentrations are important for the class of bacteria termed Halophiles.

Oxygen preferences of organisms Obligate aerobes Facultative anaerobes Obligate anaerobes

Why can some organisms grow in the presence of oxygen?

Toxic forms of oxygen need to be neutralized by enzymes –Superoxide dismutase –Catalase –Peroxidase

Oxygen Preferences of Bacteria

Candle jars increase CO 2 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

Classification based on Energy and Carbon sources

Chemical Requirements: Nitrogen Why do bacteria need nitrogen?

Chemical requirements: Sulfur and Phosphorous Why do bacteria need sulfur? Why do bacteria need phosphorous?

Chemical requirements: trace elements Small amounts of minerals Usually function as cofactors

Culture Media Chemically defined –GSA

Chemically defined media

Culture Media Complex –Nutrient Agar –TSA –BHI

Culture Media Selective Differential –Blood Selective and Differential –EMB

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