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Selective media

Medium that allows growth of certain types of bacteria while permitting growth of another, bacterial isolation

Differential media

Medium that allows one to distinguish between different microorganisms based on a difference in colony appearance (color, shape, or growth pattern) on a colony

Enriched medium

Highly nutritious material (blood, serum, yeast)


Spherical in shape






packets of 4


Packets of 8




Rod shaped






rigid or flexible


curved rod


helical and rigid


helical and flexiable

Selective agars

Phenylethyl alcohol, Crystal violet, 7.5% sodium chloride agar.

Phenylethyl alcohol agar

PEA gram positive used for isolation of most gram positive organisms.

Crystal violet agar

Gram negative, inhibitory effect on most gram positive organisms.

7.5% sodium chloride agar

Nonhalophilic, inhibitory, staphylococcus

differential/selective medium

MacConkeys agar is a good example of this because it contains bile salts and crystal violet which inhibit gram positive organisms and allow gram negatives to grow.

Differential media

contains lactose

Mannitol salt agar

yellow means mannitol positive, pink means/ carbohydrate mannitol. Staphylococci exhibit yellow zone surrounding their growth. Change in coloration

MacConkeys agar

gram negative, Either lactose negative or lactose positive, Salmonella

Coliform bacilli

Becomes red

Eosin-methylene blue agar

Only e.coli turns metallic green

Enterobacter aerogenes

Produce thick mucoid, pink colonies

Enriched media

media that have been supplemented with highly nutritious material, blood serum, yeast.


No lysis


Incomplete lysis


Complete lysis

TSI Triple sugar-iron test

designed to differentiate among the different groups of genera of the enterobacteriaceae, which are all gram negative bacilli caple of fermenting glucose with production of acid.

Alkaline slant

Red/yellow, alkaline/acid

Acid slant

Yellow/yellow, Acid/Acid

Alkaline slant

No carbohydrate fermentation, Red/Red or orange, Alkaline/Alkaline or Alkaline/No change


groups of bacteria that are found in the intertinal tract of humans and lower mammals are classified as these members.


Salmonella and Shigella

Ocasional pathogens

Proteus and Klebsiella

Normal intestinal flora

Escherichia and Enterobacter


Sulfur indole motility agar

Indole test

1/2 stab SIM (deep), cherry red, 24-48 hours

Methyl Red test

E. coli and E aerogenes. pH range of 4 positive and is red

Methyl Red test

pH range of 6 means negative and is yellow


green to deep prussian blue

Citrate positive culture

Identified by the presence of growth on the surface of the slant and is accompanied by blue color.

Citrate negative culture

Will show no growth and the medium and remain green


Forming an insoluble black ferrous sulfide precipitate that is seen along the line of the stab inoculation and in indicative of H2S production.

Urease test

urease, alkaline, deep pink

Catalase test

Hydrogen peroxide will bubble if positive, No bubble if negative.

Phenylalanine deaminase test

ammonia, green means positive, No color means negative.

Chemotheraputic agents

Chemical substance that destroy or inhibit the growth of microorganisms in living tissue.


Chemical substance used on living tissue


used on nonliving materials


Lysol solution 2% to 5%, poisonous and must be used externally. Similar to phenol.


70% to kill stuff


Tincture of iodine, iodine suspended in alcohol


Influences its effects on microorganisms with higher concentrations producing a more rapid death.

length of exposure

All microbes are not destroyed within the same exposure time. Sensitive forms are destroyed more rapidly that resistant ones.

Environmental conditions

Conditions under which a disinfectant or antiseptic affects the chemical agent, Temperature, pH. type of material on which microorganisms exist.

Normal skin flora

Skin has staphylococci, streptococci, enterococci, diptheroid, bacilli, yeast and fungus.

Genitourinary tract

trichomonas, Uti

Blood agar

Golden color, Strep and staph

Chocolate agar

gonorrhea, pink

Mueller Hinton

Black and diphtheria


Staph and yellow, pigmented or non pigmented



Phenol coefficient

Is determined by dividing the highest dilution of the chemical being tested that destroyed the microorganism in 10 minutes.

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