Recognizing the conditions necessary for microbial growth is vital to disease prevention and treatment

 The lag phase – when the bacteria are getting ready to divide  The logarithmic or exponential phase – growth of bacteria  The stationary phase – when bacterial growth begins to slow  The death phase – cell death due to the depletion of nutrients, crowding from growth, and drop in pH

 Temperature – microorganisms grow over a broad range of temp. but he optimal growth temp. for most medically important is 20°C- 45°C  Gaseous composition of the atmosphere – aerobic, anaerobic, facultative anaerobic, microaerophilic, and canophilic  Neutral pH is optimal – most media 7 or 7.5pH

 Nutritional requirements – All pathogenic bacteria are heterotrophs. Some use a wide variety of organic compounds as carbon sources; others are fastidious and require additional metabolites, vitamins, purines and pyrimidines such as Haemophilus influenzae. (Chlamydia – cell culture only)  Moisture – water is necessary for metabolic activities  Salt requirement – some microorganisms are high-salt tolerants

 Measuring cell mass  Cell weight  Turbidity – as bacteria grow in a broth culture, the broth becomes cloudy. Turbidity can be measured with a spectrophotometer and a growth curve charted on graph paper  Measurement of cell number  Direct cell counts under a microscope – good estimate but no difference between live/dead  Direct plate count – Grow dilutions of broth cultures on agar plates to determine # of colony-forming units per mL (CFU/mL) (live cells only)  Density measurement – Sample log phase culture to CFU/mL of culture and is often used to prepare dilutions for antimicrobial susceptibility testing