Question

Mailings 15.15. Differential and selective media lab (2) (Compatibility Mode] Review View . 3 3 + 1 AaBbCcDdEe AaBbCcDdEe AaBb CD AaBb CcDdl Aa ER No Spacing Heading 1 Heading 2 Normal Inhibitors Name of agar Phenylethyl alcohol Agar (PEA) Substrate None (not a differential media) Polyphenyl alcohol - affects cell membrane and DNA synthesis Indicators Notes/ expected results None (not a differential Inhibits many Gram media) negatives and some gram positives. Used to select for streptococci, enterococci, and staphylococci (all Gram positive) Columbia CNA with sheep blood agar Mannitol salt agar (MSA) Mannitol (a carbohydrate) Phenol red <pH 6.8 = yellow pH 7.4-8.4 = red > pH 8.4 = pink MacConkey agar Eosin methylene blue agar Focus

Answer 1

Columbia CNA with sheep blood agar

Inhibitor:- Nalidixic acid Antibiotic, Levaquin, quinolone

Substrate:-It is contained 5%of sheep blood mixed with TSA base or Columbia agar base. It is typically a blood agar medium. There is no substrate as it is selective media.

Indicator:- NONE

Notes:-It is a selective media that is widely used to isolate gram-positive bacteria. It is used in clinical laboratories for diagnostic purposes.

addition of nalidixic acid inhibits the growth of gram-negative bacteria and promotes the growth of gram-positive bacteria like enterococci, streptococci.

MANNITOL SALT AGAR (MSA)

Inhibitor:-

Substrate:- mannitol and sodium chloride.

• most of the non-pathogenic bacteria do not ferment mannitol whereas the pathogenic bacteria ferment mannitol
• Sodium chloride is a fermentation substrate used in MSA.

An indicator used:-Phenol red.

If the bacteria is mannitol fermenting then it produces an acidic byproduct which changes the phenol red - to yellow.

Non-fermenting bacteria:-colorless, white color

NOTES:-It is a selective and differential medium. It is used to isolate gram-positive bacteria capable of fermenting mannitol

McConkey Agar

Inhibitor:-Crystal violet and bile salts inhibit gram-positive bacteria

Substrate:-Lactose=It is used to differentiate between gram-positive bacteria based upon their ability to ferment lactose.

Indicator:- Neutral pH red. The indicator turns pink in color in case of lactose fermenting bacteria pH below 6.8

Notes:- It is a selective and differential medium used to isolate gram-negative bacteria. It differentiates gram-negative bacteria based upon their ability to ferment lactose.

EOSIN METHYLENE AGAR:-

Inhibitor:- Aniline dyes like methylene blue and eosin inhibits the growth of gram-positive bacteria.

Substrate:- none

Indicator:- Methylene blue and Eosin Yare pH indicators which form a dark purple color complex at low pH.

Notes:-EMB agar is a selective medium used to isolate gram-negative bacteria. Used to isolated coliform bacteria like E.coli