Microbial G rowth Microbiolog y Microbial Growth 0

Microbial G rowth Microbiolog y

Microbial Growth 0 In microbiology growth is defined as an increase in the number of cells. 0 Knowledge of how microbial populations expand is useful when designing methods to control microbial growth.

Factors that Affect Microbial Growth 0 Physical Factors 0 Temperature 0 p. H 0 Osmotic pressure 0 Chemical Factors

Physical Requirements 0 A. Temperature 0 Optimal growth temperature 0 Permissible range 0 human pathogens optimal = 37°C

Physical Requirements 0 Temperature 0 Psychrophile: cold loving 0 Range: 0 C-20 C 0 Mesophile: moderate temp. loving 0 Range: 20 C-40 C 0 Thermophile: heat loving 0 Range: 40 C-100 C

Physical Requirements 0 B. p. H 0 Acidophiles- “acid loving” 0 Acidity inhibits most microbial growth and is used frequently for food preservation (Ex: pickling) 0 Certain bacteria, such as those in sauerkraut and yogurt, prefer acidic environments of 6. 0 or below. 0 Fungi tend to live in slightly acidic environments p. H 5 -6. 0 Molds and yeast grow in wider p. H range, but prefer p. H between 5 and 6. 0 Neutrophiles 0 most organisms optimal p. H 6. 5 -7. 5 (near neutral) 0 Since the p. H of most human tissue is 7. 0 to 7. 2, these neutrophilic bacteria usually grow well in the body. (Most human pathogens) 0 Alkaliphiles- “alkali loving” 0 Alkalinity inhibits microbial growth, but not commonly used for food preservation. 0 Grow at p. H of 7 -12 or higher 0 Example: Vibrio cholerae optimal p. H= 9

Physical Requirements 0 C. Osmotic pressure- Cells are 80 -90 % water 0 Most bacteria require isotonic solutions (no net flow of water in either direction of cell) 0 human blood = 0. 9% Na. Cl, isotonic 0 human skin = ~3 -6% Na. Cl, hypertonic • • High Osmotic pressure In extremely salty solution, bacteria lose water through osmosis causing plamolysis (shrinking of cell mb. • Bacteria are in equilibrium with their environment • • Bacteria gain water and cell may burst This is an example of how antibiotics work

Chemical Requirements 0 A. Carbon- structural backbone of all organic compounds 0 B. Nitrogen, Sulfur and Phosphorus 0 Needed for synthesis of cellular material 0 (all above: to build organic molecules) 0 E. Trace elements: K+, Mg 2+, Ca 2+ , Fe 2+. . . 0 Used to make enzymes 0 F. Oxygen- can classify mo’s based on O 2 requirements Aerobe-requires O 2 Pseudomonas- common nosocomial pathogen Anaerobe-can’t use O 2 Clostridium bacteria Facultative-with or w/o O 2 E. coli, staphylococcus, yeast, many intestinal bacteria

Microbial Growth 0 Growth of Bacterial Cultures 0 Logarithmic representation of Bacterial Growth 0 Phases of growth 0 Bacterial Growth Curve 0 When bacteria are inoculated into a liquid growth medium, we can plot of the number of cells in the population over time.

Bacterial Growth Curve Lag phase • • Log phase Little to no growth • Pop. doesn’t increase Bacteria acclimate to new environment • Intense metabolic activity= growth in • size • Period of exponential growth with constant generation time Period of most rapid growth Cells are more susceptible to adverse environmental factors Example: antibiotics Stationary phase • • Cell growth= cell death, stability Slow microbial growth influenced by limited nutrients Low O 2 Accumulation of toxic waste Death phase • Cell death exceeds cell growth