micro media and gram positives

What is supportive media?

Media that supports the growth of most non-fastidious organism

What are two examples of supportive media?

• TSA: Trypticase soy agar (most common)

• BA or BAP: TSA 5% blood agar plate

What is BAP made of?

• trypticase soy agar base

• 5% sheep blood

What is enrichment media?

Media that enhances the growth of fastidious bacterial pathogens by supplying special nutrients or growth factors required for their reproduction

What are three examples of enrichment media?

• BCYE: Buffered charcoal-yeast extract (for legionella pneumonphila)

• CVA CAMPY: Campylobacter-blood agar

• Chocolate agar

What is selective agar?

Agar that contains elements that inhibits all but the organism type you are attempting to isolate.

What are three examples of selective media?

• CVA CAMPY agar

• PEA: phenyl-ethyl alcohol agar

• MAC: MacConkey agar

What does BCYE agar contain as enrichment?

L-cysteine

What does CVA contain as enrichment?

Brucella agar and is incubated at different atmospheric atmosphere and temperature

What does CVA contain that makes it selective?

Antibiotics

What does PEA include that makes it selective?

phenyl-ethyl alcohol, selects for gram positive cocci

What is differential media?

Media formulated so that the growth appearance of organisms provides information about the organism’s distinguishing characteristics

What does MAC contain the makes it differential?

Lactose with a neutral red indicator to distinguish between lactose fermenters from non-fermenters

What does MAC selective for?

Gram negative rods and inhibits the growth of most gram-positive bacteria

Blood agar is also differential because?

It distinguishes between different hemolytic organisms

What is enterococcus?

A gram positive cocci and major pathogen in wounds and the urinary tract

What hemolysis pattern does enterococci often demonstrate?

Gamma (can sometimes demonstrate slight alpha hemolysis)

What does BAP serve as to aerobic gram-positive cocci?

enrichment and differential agar

What types of streptococcus are alpha hemolytic?

• Viridans

• Streptococcus pneumoniae

Why are S. pneumoniae colonies green?

They produce bile starts

What types of streptococcus are beta-hemolytic?

• Group A strep

  • example: S. pyogenes

What strep is associated with strep pharyngitis?

S. pyogenes

Which organism are always characterized by their hemolytic capacities?

Streptococci

What hemolysis type should be noted for non-strep organisms?

Beta

What is Escherichia coli?

A gram negative rod, usually grows as a gray moist colony

What is e.coli on a MAC plate?

A lactose fermenter

What is a proteus?

A gram negative rod found in burn infections, UTIs and other wound infections

What kind of motion is proteus capable of?

Swarming, moves in waves across the surface of the plate. Not all proteus swarms

What does proteus look like on MAC?

Non-lactose fermenter, clear colony

What is chocolate agar used to grow?

• Neisseria meningitidis and N. gonorrheae

• Haemophilus influenzae

What does chocolate agar contain?

• X factor: hemin (from lysed cells)

• V factor: isovitalex (supplied NAD)

• Vitamin B12, minerals (Fe and Mg), cysteine and glucose

What type of environment does Neisseria gonorroeae need to grow?

An increased CO2 environment

When a genital sample is cultured what is it also subbed to?

A Thayer-Martin (TM) plate.

What is a Thayer-martin plate?

A chocolate agar base with antibiotics added which can suppress the normal flora of the female vaginal track and any skin contaminants present in male and female genital samples

The TM plate contains?

• antibiotics: Colistin ( inhibits GN), Vancomycin (inhibits GP), Nystatin (inhibits yeast), Trimethoprim (inhibits proteus)

What is a JemBec plate system?

A tm agar with a closable lid and a CO2 generating tablet for beside inoculation to assure survival of organism until it gets to the lab

What is Hektoen agar used to identify?

Salmonella and Shigella from other gram-negative rods

What do non-pathogenetic lactose-fermenting coliforms appear as on hektoen agar?

Yellow

What does Hektoen agar contain?

• bile salts: inhibit GP and are toxic to some GN

• carbohydrates: lactose, sucrose, salicin

• ferric ammonium citrate/Na thiosulfate

What is sorbitol MAC agar used for?

To detect E.coli O157:H7 from other organisms growing in the GI tract. E. coli O157:H7 does no ferment sorbitol and will appear as a colorless colony

What is Xylose-Lysine-Desocycholate (XLD) agar used for?

To isolate and differentiate Salmonella and Shigella

What does XLD agar contain?

• bile salts: inhibit GPs

• Carbohydrates (lactose, sucrose and xylose)

• ferric ammonium citrate/Na thiosulfate: detection of H2S producers

• pH indicator: phenol red

• Lysine

How does shigella appear on an XLD plate?

Colorless, shigella does not ferment carbohydrates lactose, sucrose or xylose

How does Salmonella appear on a XLD plate?

Red with blank centers as Salmonella decarboxylases lysine and is a H2S producer.

How do most non-pathogenetic enteric coliforms appear on XLD agar?

Most ferment at least on of the sugars on the plate and will produce a yellow colony

What is the H-quad plate used to identify?

Haemophilus influenzae from other Haemophilus that are normal flora in the mouth

What does the H-quad plate contain?

• horse blood quadrant (H. influenzae is non hemolytic)

• three quadrants that contain either:

  • X and V factor

  • X factor

  • V factor

What is the hemolysis pattern of S. aureus on BAP?

Beta

What kinds of agar plates can inhibit proteus swarming?

• MAC

• CNA

• PEA

What is Vaginalis (V) agar?

Enrichment media that aids in the isolation of gardnerella vaginalis in the female genital tract

What does V agar contain?

• peptones: for growth

• yeast extract: for growth

• human blood: visualization of beta hemolysis

What is Buffered Charcoal yeast extract agar (BCYE) ?

It is an enrichment medium used to isolate Legionella pneumophila

What does BCYE contain?

• yeast extract and L-cysteine to enhance growth

• activated charcoal absorbs toxic compounds that accumulate as part of the organism’s metabolism or are present following media preparation

What is Candida albicans?

A yeast that grows on skin and mucous membranes as normal flora

What does candida albicans grow best on?

Sabouraud dextrose agar

What does Candida Albicans look like on BAP?

A small white colony