LECTURE: Physical Requirements of Bacteria MICROBIOLOGY – ALCAMO LECTURE: Physical Requirements of Bacteria

Physical Requirements of Bacteria In order to kill bacteria, you need to know what conditions they need to survive Then if you take away what they need, death follows

1. Temperature Each kind of MO has its own best temp. OK a little below or above = Optimum Temp, Minimum and Maximum Reason: Enzymes only react at specific narrow temperature range

Temperature Classifications: Psychrophiles: 0 - 20C (0 - 70F) Mesophiles: 20 - 40C (70 - 100F) Pathogens: 37C (98.6F) Thermophiles: 40 - 90C (100 - 200F)

2. pH Refers to Acid/Base Balance Acid = Free H+, Base = Free OH- Scale: Acid = 1 - 6 Neutral = 7 Base = 8 - 14 Most MO grow best 6.4 – 7.5

3. Water All organisms need water as solvent for chemical reactions If water is drawn from cell, it dries out 1 – 2% ions (salt) dries out most MO

4. Oxygen Oxygen completes electrical circuit for respiration reactions “O” is last receiver of H+ = H2O Most MO need air = Aerobic Some MO have other enzyme system No Air = Anaerobic Some can be both = Facultative Very low O2 requirement = microaerophilic

5. Light Needed if photosynthetic (rare) Absence of light needed by most MO