Controlling Microbial Growth In-Vitro

Thermophiles

Thermophiles

microoganisms that grow best at high temperatures

Mesophiles

microbes that grow best at moderate temperatures

Psychrophiles

they prefer cold temperatures (like deep ocean water)

Psychrotrophs

particular group of psychrophiles, prefer refrigerator temperature

pH

refers to the acidity of alkalinity of a solution, most prefer neutral or slightly alkalin

Acidophiles (pH of 2 to 5)

Alkaliphiles (pH of >8.5)

Osmotic pressure

pressure that is exerted on a cell membrane by solutions both inside and outside the cell

Osmosis

movement of a solvent, through a permeable membrane, from a lower concentration of solutes to a higher concentration of solutes

Hypertonic

concentration of solutes in the external environment of a cell is greater than that of solutes inside the cell

Plasmolysis

condition in which cell membrane and cytoplasm of a cell shrinks away from the cell wall; occurs during hypertonic solution

Halophilic organisms

organisms that prefer to live in salty environments

Haloduric organisms

organisms that do not prefer to live in salty environment but are capable of surviving there

Piezophiles

microbes that can survive in high atmospheric pressure

Obligate aerobes

prefer the same atmosphere that humans do

Microaerophiles

they require reduced concentrations of oxygen

Obligate anaerobes

they are killed by the presence of oxygen

Capnophiles

they are microorganisms that thrive in the presence of high concentrations of carbon dioxide (CO 2)

Binary fission

process by which bacteria divides (one cell divides to become two cells)

generation time

the average interval between the birth of an individual and the birth of its offspring

Media

used to culture bacteria

chemically defined medium

Is one in which all ingredients are known

Enriched media

Is a broth of solid containing a rich supply of special nutrients that promote the growth of fastidious organisms

Ex. Chocolate agar

Selective medium

It has added inhibitors that discourage growth of certain organism

Differential medium

It permits the differentiation of organisms that grow on the medium

Ex. MacConkey agar

Viable plate count

Used to determine the number of viable bacteria in a liquid sample by making serial dilutions of the liquid and inoculation onto nutrient agar

Sterilization

It is the complete destruction of all microbes, including cells, spores, and viruses

Done by dry heat, autoclaving, gas, various chemicals, and certain types of radiation

Disinfection

the destruction or removal of pathogens from nonliving objects by physical or chemical methods

ex. pasteurization

Disinfectants

Chemical substances that eliminate pathogens on inanimate objects

Antiseptics

Solutions used to disinfect skin and other living tissues

Microbiostatic agent

Is a drug or chemical that inhibits growth and reproduction of microbes

Bacteriostatic agent

Is one that specifically inhibits the metabolism and reproduction of bacteria

Lypholization

Is a process that combines dehydration and freezing

Widely used in industry to preserve foods, antibiotics, microorganisms, and other biologic materials.

Sepsis

Refers to presence of pathogens in blood or tissues

Asepsis

Refers to the absence of pathogens

Antisepsis

Refers to the prevention of infection

Temperature and Time

2 factors that determine the effectiveness of heat for sterilization

Thermal death point (TDP)

It is the lowest temperature that will kill all of the organisms in a standardized pure culture within a specified time.

Cold

most microorganisms are not kill, but their metabolic activities are slowed

Desication

many dried organisms remain viable, but they cannot reproduce

Radiation

an ultra-violet (UV) lamp is useful for reducing the number of microbes in the air

Ultrasonic waves

Used in hospitals and medical and dental clinics to clean equipment

Filters

Used to separate cells/ microbes from liquids or gases

Gaseous atmosphere

can be altered to inhibit growth