Types Of Media

Question 1

Why do we cultivate bacteria

Answer 1

• 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

Question 2

Why should you obtain sufficient clinically relevant bacteria

Answer 2

1 test antimicrobial susceptibility
2 measure response to treatment
3 characterize agent
4 bank stain for future use

Question 3

2 practical Problems of bacteria cultivation

Answer 3

1 choice of suitable medium - ideal environment to grow bacteria

2 isolation of a bacteria in pure culture - separate it from the rest

Question 4

3 general situations in cultivation

Answer 4

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

Question 5

Describe characteristics of non-fastidious bacteria and example

Answer 5

• grow with few restrictions
• need minima nutrients and growth factors

-E Coli used in routine gene amplification and protein production

Question 6

Describe characteristics of fastidious bacteria , special conditions needed and example

Answer 6

• 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

Question 7

What is micro biome

Answer 7

-total population of bacteria in a given specimen due to numerous micro environments supporting diff microbes

Question 8

How do we identify diff microbes in a diverse specimen

Answer 8

-we set up numerous cultures with conditions to favor the diff conditions for the diff microbes found

Question 9

What are the objects of design of a media

Answer 9

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

Question 10

Culture media categorized as

Answer 10

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

Question 11

List the main types of media

Answer 11

1 liquid
2 solid
3 semi solid

Question 12

Describe liquid media characteristics and how growth is determined

Answer 12

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 )

Question 13

Describe solid media characteristics , agar and how growth is determined

Answer 13

• 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

Question 14

What is a colony and CFU

Answer 14

• population of cells arising from one cell or spore

- single cell or spore from which a population of identical cells arises

Question 15

Describe the characteristics of semi-solid media characteristics and use

Answer 15

-prepared with agar conc of less than 0.5%
Used to
1 determine bacterial motility
2 cultivation of microaerophilic bacteria

Question 16

Uses of routine lab media

Answer 16

1 to enumerate
2 remunerate
3 isolate diff bacteria

Question 17

List the types of routine media in labs

Answer 17

1 basal 
2 enriched 
3 enrichment 
4 storage 
5 transport 
6 selective 
7 differential 
8 anaerobic

Question 18

Describe characteristics and function of basal media

Answer 18

• most basic
• used for growth of non-fastidious bacteria
• used for primary isolation of microbes

Nutrient broth
Nutrient agar
Peptone water ( most basic )

Question 19

Describe nutrient agar basal media , components and function

Answer 19

• 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

Question 20

Describe characteristics and function of enriched media and types

Answer 20

• 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

Question 21

Describe characteristics , components and function of blood agar and examples of bacteria in play

Answer 21

• 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

Question 22

What is hemolysis and how do bacteria cause it

Answer 22

-streptococcus or other haemolyzing bacteria release hemolysins into agar that destroy and denature erythrocytes and hemoglobin to change the color

Question 23

Describe alpha hemolysis , color, cause and example of bacteria

Answer 23

• partial lysis of RBC
• greenish Grey or brownish discoloration around colony
• hemoglobin reduced to methemoglobin

Streptococcus pneumonia

Question 24

Describe beta hemolysis , color, cause and example of bacteria

Answer 24

• complete lysis of RBC
• clear zone in medium

Streptococcus pyogenes
Streptococcus agalactiae

Question 25

Describe gamma hemolysis , color, cause and example of bacteria

Answer 25

- no lysis | - no change in medium

Question 26

Describe chocolate agar components, function and use

Answer 26

- 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

Question 27

Fucntion of chocolate agar growth factors

Answer 27

-key support for haemophilus and neisseria

Question 28

Description and function of selective and enrichment media

Answer 28

- designed to inhibit unwanted commensal bacteria | - help / encourage of interest bacteria to grow

Question 29

Describe properties of selective media and function and examples

Answer 29

- 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

Question 30

differential growth suspension

Answer 30

differential growth suspension - suppresses growth of one at expanse of another

Question 31

Describe properties, components and functions and examples of enrichment agar

Answer 31

- 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

Question 32

Describe properties, components and use of MacConkey agar , mode of action and example of bacteria in play

Answer 32

- 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 )

Question 33

Describe properties, components and uses of transports media and examples

Answer 33

- 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

Question 34

Describe properties, components and uses of differential media and examples

Answer 34

- 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

Question 35

Examples of anaerobic media and components

Answer 35

- Robertson cooked meat medium /2.5 cm bullock heart meat / 15 ml nutrient broth -Thioglycolate broth / sodium thioglycolate /yeast extract /casein hydrolysate

Question 36

How is O2 removed in anaerobic media and how is reduced O2 measured

Answer 36

- 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

Question 37

Purpose of anaerobic media

Answer 37

-to provide media with low O2 and reduced oxidation-reduction potential and extra nutrients to anaerobes