1. Microbial Growth and The Control of Microbial Growth Microbiology

2. Microbial Growth 0 Microbial requirements for growth: 0 1. Physical 0 A. Temperature 0 Optimal growth temperature 0 Permissible range 0 human pathogens optimal = 37°C

3. Microbial Growth 0 1. Physical continued: 0 B. pH 0 most organisms optimal pH 6.5-7.5 (near neutral) 0 C. Osmotic pressure- draws the water from the cells 0 Most require isotonic solutions 0 human blood = 0.9% NaCl, isotonic 0 human skin = ~3-6% NaCl, hypertonic

4. Microbial Growth 0 2. Chemical 0 A. Carbon 0 B. Nitrogen 0 C. Sulfur 0 D. Phosphorus 0 (all above: to build organic molecules) 0 E. Trace elements: K+, Mg2+, Ca2+, Fe2+... 0 cofactors for enzymes 0 F. Oxygen 0 aerobe, anaerobe, facultative 0 G. Organic factors: vitamins, amino acids... 0 (essential organic compound an organism is unable to synthesize)

5. Microbial Growth 0 Microbial Growth 0 -for unicellular organisms, growth = increase in cell number (population) not individual cell size 0 -generation time = time required for a cell to divide 0 -both growth and death of the population is exponential, graphed on a log scale

6. Bacterial Growth Curve 0 1. Lag Phase: little to no growth, bacteria acclimate to new environment 0 2. Log Phase: period of exponential growth with constant generation time 0 3. Stationary Phase: cell growth is equal to cell death 0 4. Death Phase: cell death exceeds cell growth