Microbial Growth

Selective medium:

- Designed to suppress the growth of certain microorganisms and promote the growth of desired mircoorganisms -Useful for isolation of a specific micrioorganism from mixed culture -Sabourauds dextrose agar -EMB

Pour Plates

-Same idea as streaks, just using sequential -dilution of liquid -Sterilize before each new streak -The number of cells is diluted each time

Eosin-Methylene blue (EMB) agar:

-Selective for gram negative bacteria -Contains the dyes eosin and methylene blue, which inhibit the growth of gram-positive bacteria

Streak plates

-Sequential pattern of streaks -Sterilize before each new streak -The number of cells is diluted each time

Sabourauds dextrose agar:

Used to selectively isolate fungi. Its pH of 5.6 prevents the growth of most bacteria while allowing the growth of the fungi

What is generation time dependent on?

chemical and physical conditions

What does Microbial growth mean?

refers to an increase in size of a population

Chemically defined (synthetic medium):

-Also known as synthetic medium -Exact chemical composition is known (exact amounts of pure chemicals)`

Mannitol Salt agar is selective for:

-Bacteria of the genus Staphylococcus -Contains 7.5% NaCl, which inhibits growth of most microorganisms

Log (exponential) phase:

-Cellular reproduction is most active -Generation time is constant -Exponential increase in population -Best time to perform experiments and use antimicrobial drugs

MacConkey agar:

-Contains lactose and the dye neutral red which stains bacteria fermenting lactose -Used to identify bacteria that ferment lactose

Blood agar:

-Contains red blood cells -Used to identify bacterial species that destroy red blood cells -Beta: complete -Alpha: partial -Gamma: none

Complex medium:

-Exact composition varies from batch to batch -Usually contains yeast extracts, meat extracts, plant extracts, protein digests (peptones) -E, C, N, S are provided by proteins -Yeast or meat extracts provide vitamins and other organic growth factors

Culturing

-Growing pathogens -Inoculum is placed in medium -Microorganisms introduced into culture a medium to initiate growth Medium is the nutrient mix -Liquid: broth -Solid:tubes or petri dishes

Stationary phase:

-Growth rate slows -Due to exhausting supply of nutrients, accumulation of waste products and changes in pH -Number of new cells= number of dying cells

Death (decline) phase:

-Number of cells dying>number of new cells -Population decreases at an exponential rate -Bad time to use these cells in an experiment

Indirect measurement:

-Turbidity -Metabolic activity -Dry weight -Genetic Methods

Reducing (anaerobic) medium:

-Used to grow mircoorganisms that cannot tolerate oxygen -Contain sodium thioglycolate: combine and inactive dissolved oxygen -Reducing media are usually heated just before use to get rid of absorbed 02

Enrichment medium:

-Usually liquid -Used to grow bacteria present in small numbers in a sample containing other mircoorganisms that may be present in large numbers -Selective for the bacteria that need to be enriched

Lag Phase:

-Very little change in cell number -Synthesis of enzymes and various growth molecules (cell adapts) -The length of the lag time is dependent on growth conditions -Original culture medium and new culture medium

Differential medium:

-allows to distinguish colonies of the desired organisms from other colonies growing on the same plate -Uses the biochemical characteristics of a microorganism growing in the presence of specific nutrients or indicators added to the medium to visibly indicate the defining characteristics of a mircoorganism

Mannitol Salt agar is differential for:

-mannitol fermenters -Contains mannitol and a pH indicator that changes color if the mannitol is fermented to acid

Culture medium must what?

1) contain the appropriate nutrients (Source E, C, N, S, P, growth factors) 2) have sufficient moisture 3)pH must be appropriate 4) have a suitable level of oxygen 5) be sterile 6) be incubated at the correct temperature

What makes agar good for mircobiology?

1)Not digested (only a few mircobes) 2) Liquefies at 100 C (212 F) and remains liquid at temperature above 40 C (104 F) 3) Once solidified, remains solid up to temperature near 100 C

Turbidity:

Based on the fact that as bacteria multiply in a liquid medium, the medium becomes turbid (cloudy)

Differential medium examples:

Blood agar and MacConkey agar

What are the phases of Bacterial Growth?

Lag, Log (exponential), stationary, Death (decline)

Obtaining pure cultures:

Streak plates and Pour plates

Direct measurement:

a) Plate Counts (CFU) b) Filtration c) The Most Probable Number Method d) Direct Microscopic Count

What is agar?

is a complex polysaccharide derived from marine algae

What is generation time?

is defined as the time it takes for a population of bacterium to double in number.

What is binary fission?

one bacterium splits into two

What is a spectrophotometer used to measure?

turbidity (wavelength of 600nm)