Microbiology for Health Sciences

Oxygen

Temperature

pH

Osmotic Pressure

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

• 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

All microbes require some carbon dioxide in their metabolism

Capnophiles grow best at a higher CO2 tension than is normally present in the atmosphere

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

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.

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

[INSERT FIGURE 6.4]

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

• 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

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

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

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

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

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

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

• 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

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

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

• 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

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