1. Microbial Nutrition and Growth Microbial Ecology
Microbiology for Health Sciences

2. Factors that May Affect Growth
Oxygen Temperature pH Osmotic Pressure

3. Oxygen Requirements Aerobe: uses oxygen for metabolism
Facultative Anaerobe: does not require oxygen for metabolism
Microaerophile: requires small amounts of oxygen for metabolism
Strict Anaerobe: require element other than oxygen for metabolism, N, S, CO2

4. Several General Categories of Oxygen Requirements
Aerobe: can use gaseous oxygen in its metabolism and possesses the enzymes needed to process toxic oxygen products
Obligate aerobe: cannot grow without oxygen
Facultative anaerobe: an aerobe that does not require oxygen for its metabolism and is capable of growth in the absence of it
Microaerophile: does not grow at normal atmospheric concentrations of oxygen but requires a small amount of it in metabolism
Anaerobe: lacks the metabolic enzyme systems for using oxygen in respiration
Strict, or obligate, anaerobes: also lack the enzymes for processing toxic oxygen and cannot tolerate any free oxygen in the immediate environment and will die if exposed to it.
Aerotolerant anaerobes: do not utilize oxygen but can survive and grow to a limited extent in its presence

5. Carbon Dioxide
All microbes require some carbon dioxide in their metabolism
Capnophiles grow best at a higher CO2 tension than is normally present in the atmosphere

6. Physical Requirements for Growth
Temperature:
Psychrophiles: cold-loving microbes (-10 to 20 degrees C)
Mesophiles: moderate- temperature-loving microbes (10 to 50 degrees C)
Thermophiles: heat-loving microbes (40 to 73 degrees C)
Refrigeration severely retards the growth of most pathogenic bacteria

7. Psychrophile
A microorganism that has an optimum temperature below 15°C and is capable of growth at 0°C.
True psychrophiles are obligate with respect to cold and cannot grow above 20°C.
Psychrotrophs or facultative psychrophiles- grow slowly in cold but have an optimum temperature above 20°C.

8. Mesophile An organism that grows at intermediate temperatures
Optimum growth temperature of most: 20°C to 40°C
Temperate, subtropical, and tropical regions
Most human pathogens have optima between 30°C and 40°C

9. Temperature and Growth Requirements
[INSERT FIGURE 6.4]

10. Thermophile
A microbe that grows optimally at temperatures greater than 45°C
Vary in heat requirements
General range of growth of 45°C to 80°C
Hyperthermophiles- grow between 80°C and 120°C

11. Environmental Factors that Influence Microbes
Temperature Adaptations
Microbial cells cannot control their temperature, so they assume the ambient temperature of their natural habitat
The range of temperatures for the growth of a given microbial species can be expressed as three cardinal temperatures:
Minimum temperature: the lowest temperature that permits a microbe’s continued growth and metabolism
Maximum temperature: The highest temperature at which growth and metabolism can proceed
Optimum temperature: A small range, intermediate between the minimum and maximum, which promotes the fast rate of growth and metabolism
Some microbes have a narrow cardinal range while others have a broad one
Another way to express temperature adaptation- to describe whether an organism grows optimally in a cold, moderate, or hot temperature range

12. pH Requirements pH: low pH = acidic, high pH = basic pH range 0-14
Normal growth range for bacteria is pH 6 to 8 (most bacteria can’t grow in orange juice)
Acidophiles (minority) can grow in pH 4
Molds and yeasts grow in pH 4-6

13. Effects of pH
Majority of organisms live or grow in habitats between pH 6 and 8
Obligate acidophiles
Euglena mutabilis- alga that grows between 0 and 1.0 pH
Thermoplasma- archae that lives in hot coal piles at a pH of 1 to 2, and would lyse if exposed to pH 7

14. Osmotic Pressure
Most microbes live either under hypotonic or isotonic conditions
Osmophiles- live in habitats with a high solute concentration
Halophiles- prefer high concentrations of salt
Obligate halophiles- grow optimally in solutions of 25% NaCl but require at least 9% NaCl for growth

15. Osmotic Pressure
Osmotic pressure: addition of salts to foods results in shrinkage of cell due to loss of water
Plasma membrane pulls away from cell wall which results in inhibition of cell growth
Ex. In food prep = salted fish, honey, sweetened and condensed milk (addition of high amounts of salt or sugar)
Halophiles: org. that can grow in high salt concentrations

16. Ecological Associations Among Microorganisms
Most microbes live in shared habitats
Interactions can have beneficial, harmful, or no particular effects on the organisms involved
They can be obligatory or nonobligatory to the members
They often involve nutritional interactions

17. Symbiosis
A general term used to denote a situation in which two organisms live together in a close partnership

18. Symbiosis
A general term used to denote a situation in which two organisms live together in a close partnership
Mutualism: when organisms live in an obligatory but mutually beneficial relationship

19. Symbiosis A general term used to denote a situation in which two
organisms live together in a
close partnership
Commensalism: the member called the commensal receives benefits, while its coinhabitant is neither harmed nor benefited
Satellitism: when one member provides nutritional or protective factors needed by the other

20. Symbiosis A general term used to denote a
situation in which two organisms
live together in a close
partnership
Parasitism: a relationship in which the host organism provides the parasitic microbe with nutrients and a habitat

21. Nonsymbiotic Relationship
Organisms are free-living and relationships are not required for survival
Synergism: an interrelationship between two or more free-living organisms that benefits them but is not necessary for their survival
Antagonism: an association between free-living species that arrises when members of a community compete
One microbe secretes chemical substances into the surrounding environment that inhibit or destroy another microbe in the same habitat

22. Interrelationships Between microbes and Humans
Normal microbiotia: microbes that normally live on the skin, in the alimentary tract, and in other sites in humans
Can be commensal, parasitic, and synergistic relationships