Specialized Media Flashcards
General Purpose Media
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
Reducing Media
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
Transport Media
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
Specialized Media
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
Specialized Media: Enriched Media
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)
Enriched Media: Chocolate Agar
Used for growing fastidious organisms such as Neisseria and Haemophilus
Enriched: Hemolyzed sheep blood
Enriched and Differential Media: Blood Agar (BAP)
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
Hemolytic Enzymes
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
Hemolytic Patterns For Alpha Hemolysis
partial hemolysis
- S. pneumoniae
- S. viridians
Hemolytic Patterns For Beta Hemolysis
completely obliterated
- S. pyogenes
- S. Agalactiae
Hemolytic Patterns For Gamma hemolysis
ghost hemolysis; no hemolysis; no lysis of RBC’s
- E. faecalis
- Strep Bovis
Selective Media
- 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
Selective Media: Phenylethyl Alcohol Agar (PEA)
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
Differential Media
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
Mannitol Salt Agar
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)
MacConkey’s Agar
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)
Eosin Methylene Blue Agar
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
Hektoen Enteric Agar
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
Multi-Test Media: Enterotube II System
- 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
Before Incolulating A Enterotube
- Gram Stain- isolate must be Gram Negative (-) rods
- 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
Chromogenic Media
-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
CHROMagar for urine cultures
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)
CLED agar
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
Both Selective and Differential Media
- Mannitol Salt Agar
- MacConkey’s Agar
- Eosin Methylene Blue Agar
- Hektoen Enteric Agar
Differential Media: Examples
- Multi-test media: Enterotube II System
- Chromogenic Media
- CLED agar
Selective Media: Examples
-Phenylethyl Alcohol agar (PEA)
