Microbial Growth For microorganisms, growth is measured by increase in cell number, due to their limited increase in cell size.

Bacteria are classified by: Temperature Range pH Range Osmotic Pressure Need for Oxygen

Other Classifications Facultative: Microorganisms that can grow in more than one environment Obligate: Microorganisms that have specific environments strictly needed for growth

Temperature Range Psychrophile: 0-30 degrees C range, 15 C optimum growth temperature Mesophile: degrees C range, 37 C optimum growth temperature. These have most pathogens, optimized for body temperature. Thermophile: degrees C range, 55 C optimum growth temperature.

pH Range Acidophiles: Grow in acidic environment, pH less than 6.5. Linked to stomach ulcers. Neutrophiles: Grow in neutral environment, pH Most pathogens are neutrophiles, as your body is mostly within this pH range. Alkaliphiles: Grow in basic environments, pH greater than 7.5.

pH PH a factor in food spoilage: Canned food high in botulism Acid rain effect the environment Bacteria often produce acids that eventually interfere w/ their own growth.

Osmotic Pressure Range Low osmotic pressure kills many prokaryotes. Halophiles: microbes that can survive in salty environments. Obligate Halophiles: microbes that need salty environments to survive.

Nutritional Requirements for Growth Carbon: All living things need a carbon source Nitrogen: used in protein and nucleic acid synthesis Sulfur: used in protein synthesis Phosphorus: Used in ATP and nucleic acids Trace Elements: (Fe, Zn, Cu, etc.) Co-factors and co-enzymes to activate enzymes.

Nutritional Requirements Cont. Trace Elements: (Fe, Zn, Cu, etc.) Co-factors and co-enzymes to activate enzymes. Only in small amounts. Organic Growth Factors are organic compounds that are essential to the organism but the organism is unable to synthesize it itself (ex. Vitamins, amino acids, nucleotides).

Classifications for Oxygen Need Obligate Aerobes: Must have free oxygen for aerobic respiraiton. Obligate Anaerobes: Killed by free oxygen. Growth only occurs where there is no oxygen.

Oxygen Needs Cont. Facultative Anaerobes: Have both aerobic and anaerobic growth. Growth is greater in the presence of oxygen because full respiration occurs. Aerotolerant anaerobes: Only anaerobic growth, but can tolerate the presence of oxygen. Growth occurs evenly throughout media as oxygen has no effect.

Oxygen Needs Cont. Microaerophiles: Only aerobic growth. Oxygen is required in low concentrations. Growth occurs only where a low concentration of oxygen has diffused into the medium.

Bacteria classified according to their Oxygen needs Obligate aerobes – Must have free oxygen for aerobic respiration – Grow only occurs on top of media where there is high concentration of oxygen

Bacteria classified according to their Oxygen needs Falcutative Anaerobes – Both aerobic and anaerobic growth – Growth is greater in the presence of oxygen. – Growth occurs throughout media.

Bacteria classified according to their Oxygen needs Obligate anaerobes – killed by free oxygen – Growth occurs only where there is no oxygen

Bacteria classified according to their Oxygen needs Aerotolerant Anaerobes – Only anaerobic growth; but can tolerate the presence of oxygen – Growth occurs evenly throughout media as oxygen has no effect

Bacteria classified according to their Oxygen needs Microaerophiles – Only aerobic growth – oxygen is required in low concentrations. – Growth occurs only where a low concentration of oxygen has diffused into medium

Culture, Colony and Culture Media Culture: The actual bacteria being grown. Colony: A group of the same bacteria growing together. Culture Media: What the bacteria are growing on or in.

Culture Media Two types of culture media Broth: A liquid nutrient media without agar Agar: a common solidifying agent for a culture medium.

Agar It is added to nutrient medium to solidify it in order to bacterial grow colonies. It is made form seaweed. It has long been used in various foods from jellies, soups, and ice cream. Few microbes can break down agar. Different freezing/melting points. Solid to liquid at 94 C, liquid to solid at 42 C. Labs keep it liquid at 50 C

Culture Media Cont. Chemically Defined: Medium in which the exact chemical composition is known. Often used to grow fastidious organisms. Expensive to buy. Complex: Used to grow most of the common bacteria and fungi that would be used in an introductory lab. Made of nutrients such as extracts from yeast, meat and plants. Anaerobic Growth Media/Reducing Media: No free oxygen and used to grown obligate anaerobes.

Culture Media Cont. Selective: Media that is designed to suppress the growth of unwanted bacteria and encourage the growth of wanted bacteria. Differential: Makes it easier to distinguish colonies of the desired organism from other colonies growing on the same plate. Enrichment: Used to encourage the growth of a particular organism in a mixed culture. Example soil, fecal samples etc...