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Microbiology for Health Sciences. Oxygen Temperature pH Osmotic Pressure.

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Presentation on theme: "Microbiology for Health Sciences. Oxygen Temperature pH Osmotic Pressure."— Presentation transcript:

1 Microbiology for Health Sciences

2 Oxygen Temperature pH Osmotic Pressure

3  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 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  All microbes require some carbon dioxide in their metabolism  Capnophiles grow best at a higher CO 2 tension than is normally present in the atmosphere

6  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  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  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


10  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 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: 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  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  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: 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  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 A general term used to denote a situation in which two organisms live together in a close partnership

18 Mutualism: when organisms live in an obligatory but mutually beneficial relationship

19 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 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 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  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

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