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Microbiology Lab > Specialized Media > Flashcards

Specialized Media Flashcards

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1
Q

General Purpose Media

A

Tryptic soy agar (TSA), Nutrient agar (NA), and Brain Heart Infusion (BHI)

  • Designed to grow bacteria and fungi that do not have special growth requirements
  • Nonselective
  • Complex formula (not chemically definable) that contains milk protein (casein), soybean protein and sodium chloride
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2
Q

Reducing Media

A

Thioglycolate broth

  • It helps determine oxygen requirements of isolates
  • It allows the growth of anaerobic bacteria
  • Thioglycollic acid slows the penetration of oxygen reducing its availability
  • Thioglycolate will allow ALL organisms to grow
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3
Q

Transport Media

A

Amie’s, Stuart’s, and Cary Blair
-Temporary- keeps bacteria alive until it can be cultured in the lab
-Prevents the specimen from drying out
-Prevents normal flora from overgrowing the pathogen
>Contain buffers, salts, and other chemical agents to inhibit growth until specimen can be cultured
>May contain charcoal to absorb toxins
-Transport media is available in many forms to allow for the proper collection of different specimens
-There are vials for tissue samples and scrapings, stool and urine samples, swabs and formalin filled vials

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4
Q

Specialized Media

A

Designed to quickly identify pathogens
-Enriched Media
-Selective Media
-Differential Media
>Media can be both differential and selective
>Media can be both enriched and differential

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5
Q

Specialized Media: Enriched Media

A

Enriched media has added nutrients from blood, serum, hemoglobin, eggs or growth factors such as vitamins, minerals which allow fastidious organisms to grow

  • Blood agar (whole sheep, rabbit or horse blood)
  • Chocolate agar (hemolysed blood)
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6
Q

Enriched Media: Chocolate Agar

A

Used for growing fastidious organisms such as Neisseria and Haemophilus
Enriched: Hemolyzed sheep blood

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7
Q

Enriched and Differential Media: Blood Agar (BAP)

A

Used to cultivate Staphylococcus, Streptococcus and other fastidious pathogens
-used to grow fastidious organisms
-used to identify hemolytic exotoxins
-used to identify hemolytic patterns:
>B (beta) hemolytic= S. pyogenes
>a (alpha) hemolytic= S. pneumoniae
-Tryptic (trypticase) soy plus 5% sheep/rabbit blood

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8
Q

Hemolytic Enzymes

A

Bacterial Exotoxins
-Alpha hemolysins: cause partial lysis of RBC’s
> alpha hemolytic organisms have a green halo around the colony
-Beta hemolysins: cause complete lysis of RBC’s
> Beta hemolytic organisms have a clear halo around the colony
-Gamma: no lysis of RBC’s
>Gamma hemolytic there is no hemolysis

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9
Q

Hemolytic Patterns For Alpha Hemolysis

A

partial hemolysis

  • S. pneumoniae
  • S. viridians
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10
Q

Hemolytic Patterns For Beta Hemolysis

A

completely obliterated

  • S. pyogenes
  • S. Agalactiae
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11
Q

Hemolytic Patterns For Gamma hemolysis

A

ghost hemolysis; no hemolysis; no lysis of RBC’s

  • E. faecalis
  • Strep Bovis
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12
Q

Selective Media

A
  • Media inhibits one group of organisms while allowing another to grow
  • Chemical additives added to selective media include: Salt, Bile salts, Dyes, Alcohols and antibiotics
  • Selective media can be used to inhibit the growth of normal flora so pathogens can be isolated
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13
Q

Selective Media: Phenylethyl Alcohol Agar (PEA)

A

PEA is selective for Gram Positive (+) organisms
-Phenylethyl alcohol is bacteriostatic for Gram Negative (-) bacteria:
>Dissolves the lipopolysaccharide outer layer of the cell wall
> Inhibits DNA synthesis

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14
Q

Differential Media

A

Differential media is designed to show when a particular biochemical reaction has taken place helping to identify an organism
-Not all bacteria have the same enzymes
-The ability to ferment a sugar or use an amino acid can help identify the organism
>Bacterial enzyme–> biochemical reaction–> color change

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15
Q

Mannitol Salt Agar

A

Selective and Differential
>Selective:
-7.5% salt-prevents all bacteria from growing, except Staphylococcus

> Differential:

  • Mannitol (sugar) and Phenol Red
  • Mannitol can be fermented by the pathogen S. aureus
  • Growth with no Mannitol fermentation= S. epidermidis (light colored growth and colored red)
  • Growth and Mannitol fermentation= S. aureus and S. saprophyticus (heavy colored growth and colored yellow)
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16
Q

MacConkey’s Agar

A

Selective and Differential
>Selective:
-Crystal violet and Bile salts inhibit Gram Positive (+) organisms; allowing for Gram Negative (-) (Enterobacteriaceae) to grow

>Differential:
-Lactose and Neutral Red
-Lactose fermentation leads to acid production 
(lactose + turns into purple growth)
(lactose negative is clear growth)
17
Q

Eosin Methylene Blue Agar

A

Selective and Differential
>Selective:
-Eosin and methylene blue dyes inhibit Gram Positive (+) organisms; allows for Gram Negative (-) (Enterobacteriaceae) to grow

> Differential:

  • Lactose, eosin and methylene blue
  • Fermentation of the sugar leads to acid production
  • Lactose Positive (+) Fermentation= E.Coli (metallic green /blue color growth)
  • Lactose Negative (-) No Fermentation= Salmonella/ Shigella
18
Q

Hektoen Enteric Agar

A

Selective and Differential
>Selective:
-Bile salts inhibit Gram Positive (+) organisms
-Used to identify Salmonella and Shigella and other Gram Negative (-) enteric organisms

> Differential:

  • Lactose, sucrose and salicin
  • Salmonella and Shigella cannot ferment the sugars and grow blue-green colonies
  • Sodium thiosulfate (sulfur source)
  • Salmonella reduces sulfur to hydrogen sulfide and forms a black precipitate
  • used to test food containing poultry, eggs and dairy products
19
Q

Multi-Test Media: Enterotube II System

A
  • System performs 15 biochemical test on a colony
  • A system containing differential media designed to identify Gram Negative (-) bacteria
  • Used to identify Gram Negative (-) rods in the family Enterobacteriaceae such as Salmonella, Shigella, E. coli, Serratia, Klebsiella, etc.
  • Each compartment of the Enterotube contains differential media that have various carbohydrates, amino acids, etc.
  • The tech “reads” each compartment looking for a color change in the media
  • Only positive results are circled on a code pad
  • The 5 digit “biocode” corresponds to an organism
20
Q

Before Incolulating A Enterotube

A
  1. Gram Stain- isolate must be Gram Negative (-) rods
  2. Oxidase Test- isolate must be Oxidase Negative (-)
    -Oxidase test is done to differentiate organisms in the family Enterobacteriaceae from the family Pseudomonadaceae
    >Oxidase Negative= Enterbacteriaceae- use the Enterotube II System
    >Oxidase Positive= Pseudomonadaceae- use the Oxiferm System
21
Q

Chromogenic Media

A

-Specialized media designed for urinary tract infections and detecting pathogens in the environment
-Preliminary screening for UTI and food pathogens
-Faster results- simplify culture technique
-Used to detect, identify, and quantify pathogens
-Various chemical compositions allow detection of key clinical and food-borne pathogens
> Salmonella, Staph aureus, E. coli, Pseudomonas, Vibrio, Listeria, Candida

22
Q

CHROMagar for urine cultures

A

Chromogenic media

  • differential media that contains enzyme substrates linked to a color reaction
  • If bacteria contain the enzymes needed to utilize a substrate a specific color develops
  • A colony count streak plate allows for enumerating organisms, as well as identifying the isolate (qualitative and quantitative)
23
Q

CLED agar

A

Cystine- amino acid
Lactose- carbohydrate
Electrolyte deficient- prevents swarming
-Differential Media designed to grow and quantify pathogens in urines
-pH indicators help colonies develop different colors to identify organisms

24
Q

Both Selective and Differential Media

A
  • Mannitol Salt Agar
  • MacConkey’s Agar
  • Eosin Methylene Blue Agar
  • Hektoen Enteric Agar
25
Q

Differential Media: Examples

A
  • Multi-test media: Enterotube II System
  • Chromogenic Media
  • CLED agar
26
Q

Selective Media: Examples

A

-Phenylethyl Alcohol agar (PEA)

Microbiology Lab (19 decks)

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