Types Of Media Flashcards
Why do we cultivate bacteria
- grow and isolate bacteria in an infection
- definitive identification and characterization
- determine which bacteria is causing infection
- determine which bacteria is a contaminant or colonizer
Why should you obtain sufficient clinically relevant bacteria
1 test antimicrobial susceptibility
2 measure response to treatment
3 characterize agent
4 bank stain for future use
2 practical Problems of bacteria cultivation
1 choice of suitable medium - ideal environment to grow bacteria
2 isolation of a bacteria in pure culture - separate it from the rest
3 general situations in cultivation
1 to amplify defined bacteria clone with purpose or increasing amount produce
2 to quantify and identify types of organism in specimen
3 isolate a particular type of microbe in specimen from rest
Describe characteristics of non-fastidious bacteria and example
- grow with few restrictions
- need minima nutrients and growth factors
-E Coli used in routine gene amplification and protein production
Describe characteristics of fastidious bacteria , special conditions needed and example
- require specific growth conditions that stimulate their natural conditions
- have numerous restrictions
- may require extract of host tissue to include all growth factors
- needs suitable source or nutrients
Obligate intracellular bacteria: chlamydia and rickettsiae require viable eukaryotic cells to grow in and we infect eukaryotic cell to amplify them
What is micro biome
-total population of bacteria in a given specimen due to numerous micro environments supporting diff microbes
How do we identify diff microbes in a diverse specimen
-we set up numerous cultures with conditions to favor the diff conditions for the diff microbes found
What are the objects of design of a media
1 grow pathogenic bacteria of interest
2 separate of interest microbe from rest by inhibiting growth of ones we don’t want
3 differentiate their phenotypic properties for proper identification
Culture media categorized as
1 chemical - where chemical composition is known for specific media
2 complex - has extracts and digests of plants , meats of yeast when for bacterial growth
List the main types of media
1 liquid
2 solid
3 semi solid
Describe liquid media characteristics and how growth is determined
1 has a defined salt concentration
2 has source of protein ( peptone or casein )
3 fastidious require growth factors to be added
4 aka broth media
5 growth determined by increase in opacity ( turbidity )
Describe solid media characteristics , agar and how growth is determined
- it’s broth media which is solidified by seaweed extracts called agar
- agar is a complex polysaccharide , not metabolized by bacteria , liquified at 100 and solidifies at 40
- growth identified as colonies
What is a colony and CFU
- population of cells arising from one cell or spore
- single cell or spore from which a population of identical cells arises
Describe the characteristics of semi-solid media characteristics and use
-prepared with agar conc of less than 0.5%
Used to
1 determine bacterial motility
2 cultivation of microaerophilic bacteria
Uses of routine lab media
1 to enumerate
2 remunerate
3 isolate diff bacteria
List the types of routine media in labs
1 basal 2 enriched 3 enrichment 4 storage 5 transport 6 selective 7 differential 8 anaerobic
Describe characteristics and function of basal media
- most basic
- used for growth of non-fastidious bacteria
- used for primary isolation of microbes
Nutrient broth
Nutrient agar
Peptone water ( most basic )
Describe nutrient agar basal media , components and function
- peptone / source of N2
- beef extract / salts , carbohydrates, organic N2 compounds
Used for
1 enumeration of organisms in water, sewage , waste and dairy specimen
2 cultivation and maintenance of non-fastidious species
Describe characteristics and function of enriched media and types
- addition of extra nutrient to basal in form of blood, serum or egg yolk
- used for fastidious bacteria eg haemophilus , influenza
1 chocolate agar
2 blood agar
3 Dorset egg
Describe characteristics , components and function of blood agar and examples of bacteria in play
- peptone / growth for non-fastidious bacteria
- casein soy meat / growth of fastidious
- NaCl / nutrient reserve
- blood ( sheep or horse )/ nutrients, support haemophilus , neisseria
- allow for detection of haemolytic organisms eg streptococcus or staphylococcus
What is hemolysis and how do bacteria cause it
-streptococcus or other haemolyzing bacteria release hemolysins into agar that destroy and denature erythrocytes and hemoglobin to change the color
Describe alpha hemolysis , color, cause and example of bacteria
- partial lysis of RBC
- greenish Grey or brownish discoloration around colony
- hemoglobin reduced to methemoglobin
Streptococcus pneumonia
Describe beta hemolysis , color, cause and example of bacteria
- complete lysis of RBC
- clear zone in medium
Streptococcus pyogenes
Streptococcus agalactiae
Describe gamma hemolysis , color, cause and example of bacteria
- no lysis
- no change in medium
Describe chocolate agar components, function and use
- has peptone, casein soy meat NaCl and blood
- blood added to hot agar causing RBC to lyse and release growth factors 5 and 10 and give rich brown color
Fucntion of chocolate agar growth factors
-key support for haemophilus and neisseria
Description and function of selective and enrichment media
- designed to inhibit unwanted commensal bacteria
- help / encourage of interest bacteria to grow
Describe properties of selective media and function and examples
- soild ( agar based )
- isolation of individual colonies
- made selective by inhibitors that affect commensal agents and not of interest one
Thayer Martin agar
MacConkey agar
Mannitol salt agar
TCBS agar
differential growth suspension
differential growth suspension - suppresses growth of one at expanse of another
Describe properties, components and functions and examples of enrichment agar
- liquid
- to increase conc of at interest microbe whilst inhibiting others prior to plating on solid media
- inhibitory factors suppress commensal
Alkaline peptone water
Vibrial cholera
Selenite F broth - stool pathogens eg salmonella
Describe properties, components and use of MacConkey agar , mode of action and example of bacteria in play
- selective differential medium of enterobacteriaceae from specimens
- has bile salts and crystal violet ( inhibit gram +ve )
- neural red indicator ( pH 6.8 and red )
-has lactose
-fermenter bacteria will ferment lactose to lactic acid reduced pH and indicator goes pink
( k pneumonia, enterobacter )
-non fermenter won’t change color
( salmonella , shigella )
Describe properties, components and uses of transports media and examples
- can be liquid , solid , semi solid or basal with additives that maintain viability of organisms while inhibiting growth of more Robust organisms
- used to transport specimen from source to lab
1 Stuart’s media
2 amies media
3 Cary blur transport media
Describe properties, components and uses of differential media and examples
- has substrates metabolized by bacteria and by products impose unique color on colony
- allow growth of more than one microbe but with morphological changes
TCBS
Blood agar
MacConkey agar
Mannitol salt agar
Examples of anaerobic media and components
- Robertson cooked meat medium
/2.5 cm bullock heart meat
/ 15 ml nutrient broth
-Thioglycolate broth
/ sodium thioglycolate
/yeast extract
/casein hydrolysate
How is O2 removed in anaerobic media and how is reduced O2 measured
- boil to remove O2 and seal with sterile liquid paraffin
- add 0.1% glucose , 0.1% thioglycolate , 0.1% ascorbic acid , 0.05% cysteine or red hot iron fillings
-used methylene blue indicator
/ colorless under reduced conditions
Purpose of anaerobic media
-to provide media with low O2 and reduced oxidation-reduction potential and extra nutrients to anaerobes
