Microbiology Part 5

Pure culture

A single “strain” of microbe grown in isolation

Strain

A microbial culture which is the descendent of a single cell originally isolated from the environment

Aseptic technique

Method of handling material without contamination from the environment

Batch culture

A limited amount of liquid growth medium is added to a flask

Continuous culture

The medium is continually replenished and waste culture is continually removed

Carbon, nitrogen, sulfur, and phosphorus

What do all living cells need a source of that is in medium?

Agar-based medium

Medium that is derived from red algae, microbes cannot break it down, perfect surface for microbes

Complex medium

A medium that has complex ingredients with chemically undefined composition

Defined medium

The exact chemical composition of the medium is known

Selective medium

Contains agents that selectively inhibit some of the microbes present while allowing the desired species to grow

Differential medium

Contains agents that allow different species to be visually differentiated

Blood agar

Medium useful for differentiating streptococcal species, alpha, beta, and gamma can be observed, hemolysis is evident

MacConkey agar

Selective and differential medium for lactose, peptone, and bile salts, with neutral red as a pH indicator

Baird-parker agar

Medium used for isolating gram positive bacterium S. aureus colonies are black in color with a halo around

Mannitol salt agar

Complex, selective, and differential medium, high salt concentration is selective for staph because it is salt tolerant

Direct microscopic count

A microscope is used to determine the number of cells is microscopic field of known volume

Viable cell counts

Cells are plated onto solid growth medium and the number of colonies are counted

Turbidimetric measurements

The optical density of the culture is used as an indicator of cell numbers

All cells in suspension are capable of forming a colony and all colonies arise from a single cell

What assumptions does the viable cell counts make?

Spectrophotometer

An instrument that can measure the “cloudiness” of a culture, by measuring the absorbance or optical density

Binary fission

Many microorganisms multiply by simple diffusion, two daughter cells are produced by symmetric division of the parent cell

Budding

Production of daughter cells by asexual reproduction by producing a bud at one pole of the cell

Exponential growth

What growth patterns do bacteria follow?

Stationary phase

As numbers increase they run out of nutrients and inhibitory metabolic end products accumulate, the numbers “plateau”

Lag phase

Period when bacteria are adapting to their environment

Death phase

The loss of cells in the stationary phase culture from lack of nutrients

Obligate aerobes

Cannot grow in the absence of O2

Obligate anaerobes

Cannot grow in the presence of O2

Facultative anaerobes

Can grow either with or without molecular oxygen

Aerotolerant anaerobes

Metabolism is anaerobic but they are unaffected by the presence of oxygen

Microaerophiles

Require limited oxygen for growth

Reactive oxygen species

Oxygen react with enzymes in the cell include hydrogen peroxide, superoxide radical

Catalase and peroxidase, superoxide dismutase

Which enzymes remove hydrogen peroxide in O2 tolerant species? Superoxide radical?