culture media

solid media

used for the isolation of bacteria as pure culture

agar

most commonly used to prepare solid media

a polysaccharide extract obtained from seaweed

agar

bacteriologically inert, it has no influence on bacterial growth

remains solid 37%C

it is transparent

agar

bacteria may be identified by studying the colony character

mixed bacteria can be separated

liquid media

used for profuse growth

mixed bacteria cannot be separarted

chemical composition

chemically defined media prepared from pure chemical substances

used in research work

basal media

enriched media

selective media

indicator media

transport media

storage media

6 types of routine laboratory media

basal media

those may be used for growth (culture) of bacteria that do not need enrichment of media

enriched media

the media are enriched usually by adding blood, serum or egg

selective media

this media favor the growth of a particular bacterium by inhibiting the growth of undesired bacteria and allowing growth of desirable bacteria

differential (indicator) bacteria

an indicator is included in the medium

particular organism causes change in the indicator

transport media

these media are used when specimen cannot be cultured soon after collection

storage used for storing the bacteria for a long period of time

storage media

nutrient broth

uses as a basal media for the preparation of other media

to study soluble products of bacteria

nutrient broth

components: 500g meat is minced and mixed with 1L water

10g peptone and 5g sodium chloride are added, pH is adjusted to 7.3

nutrient agar

it is solid at 37 degrees Celsius 2.5% agar is added in nutrient broth

it is heated at 100 degrees Celsius to melt the agar and then cooled

peptone water

used as base for sugar media and to test indole formation

blood agar

5-10% defibrinated sheep or horse blood is added to melted agar 45-50 degrees Celsius

blood agar

most commonly used medium

blood acts as an enrichment material and also an indicator

beta hemolysis

alpha hemolysis

gamma hemolysis

types of changes (hemolysis)

beta hemolysis

the colony is surrounded by a clear zone of complete hemolysis

alpha hemolysis

colony is surrounded by a zone of greenish discoloration due to formation of biliverdin

gamma hemolysis

there is no change in the medium surrounding the colony

no hemolysis

chocolate agar or heated blood agar

prepared by heating blood agar

heating the blood agar inactivates inhibitor of growths

chocolate agar or heated blood agar

used for culture pneumococcus, gonococcus, meningococcus, and haemophilus

MacConkey agar

it contains agar, peptone, sodium chloride, bile salt, lactose and neutral red

MacConkey agar

most commonly used for Enterobacteriaceae

it is selective and indicator medium

selective medium

as bile salt does not inhibit the growth of Enterobacteriaceae but inhibits growth of many other bacteria

differential medium

as the colonies of bacteria that ferment lactose take a pink color due to production of acid

acid

turns indicator neutral red to pink

colorless colony

indicates that lactose is not fermented

Mueller Hinton Agar

disc diffusion sensitivity test for antimicrobial drugs would be carried out in this media as per WHO recommendation

Hiss’s Serum water medium

used to study the fermentation reactions of bacteria which cannot grow in peptone water sugar media

lowenstein-Jensen medium

it contains egg, malachite green and glycerol

egg

an enrichment material which stimulates the growth of tubercle bacili

malachite green

inhibits growth of organisms other than mycobacteria

glycerol

promotes the growth of mycobacterium tuberculosis but not mycobacterium bovis

lowenstein-Jensen medium

used to culture tubercle bacilli

dubos medium

in this medium drug sensitivity of tubercle bacilli can be carried out

dubos medium

it contains tween 80, bovine serum albumin, casein hydrolysate, asparagin and salts

loeffler serum

diphtheria bacilli grow in this medium in 6 hours when the secondary bacteria do not grow

loeffler serum

used for rapid diagnosis of diphtheria and to demonstrate volutin granules

tellurite blood agar

used as a selective medium for isolation of Corynebacterium diphtheriae

tellurite blood agar

an indicator medium as te diphtheria bacilli produce black colonies

tellurite

inhibits the growth of most secondary bacteria without an inhibitory effect on diphtheria bacilli

tellbrism

metabolized by tellurite which produces black color

eosin-methylene blue agar

a selective and differential medium for enteric gram negative rods

xylose lysine deoxycholate (XLD Agar)

a selective media used to isolate salmonella and shigella species from stool specimens

salmonella-shigella agar (SS Agar)

a selective medium used to isolate salmonella and shigella species

deoxycholate citrate agar

a selective medium also a differential indicator medium used for isolation of salmonella and shigella

tetrathionate broth

acts as a selective medium that inhibits normal intestinal bacteria and permits multiplication of salmonella

used for isolating salmonella from stool

selenite F Broth

same as that tetrathionate broth

thiosulphate-citrate-bile-sucrose (TCBS) agar

a selective medium used to isolate Vibrio cholerae and other vibrio species from stool

charcoal-yeast agar

increased concentration of iron and cysteine allows growth

used for legionella pneumophilia

tellurite-gelatin agar medium

may be used as transport, selective and indicator medium

campylobacter medium

a selective medium used to isolate campylobacter jejuni and campylobacter coli from stool

cary-blair medium

used to transport medium for feces that may contain salmonella, shigella, vibrio or campylobacter species

amies medium

used for gonococci and other pathogens

peptone water sugar media

the media are colorless used to study sugar fermentation

motility indole urea medium

used to differentiate enterobacteria species by their motility, urease, and indole reactions

kligler iron agar

a differential slope medium used in identification of enteric bacteria

christensen’s urea medium

used to identify urea splitting organisms

puple pink

what color indicates urea splitting

bordet-gengou medium

contains agar, NaCl, glycerol, peptone and 50% horse blood used for culture of bordetella pertussis