Microbial Growth and The Control of Microbial GrowthMicrobiology

Microbial Growth0Microbial requirements for

growth:01. Physical

0 A. Temperature0Optimal growth temperature0Permissible range0human pathogens optimal =

37°C

Microbial Growth01. Physical continued:

0 B. pH0most organisms optimal pH 6.5-7.5 (near neutral)

0 C. Osmotic pressure- draws the water from the cells0Most require isotonic solutions0human blood = 0.9% NaCl, isotonic0human skin = ~3-6% NaCl, hypertonic

Microbial Growth02. Chemical

0 A. Carbon0 B. Nitrogen0 C. Sulfur0 D. Phosphorus0 (all above: to build organic molecules)0 E. Trace elements: K+, Mg2+, Ca2+, Fe2+...

0cofactors for enzymes0 F. Oxygen

0aerobe, anaerobe, facultative0 G. Organic factors: vitamins, amino acids...

0(essential organic compound an organism is unable to synthesize)

Microbial Growth0Microbial 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

Bacterial Growth Curve

0 1. Lag Phase: little to no growth, bacteria acclimate to new environment0 2. Log Phase: period of exponential growth with constant generation

time0 3. Stationary Phase: cell growth is equal to cell death0 4. Death Phase: cell death exceeds cell growth