Review Questions Describe the chemical features that make Desoxycholate Agar Sel

Question

Review Questions Describe the chemical features that make Desoxycholate Agar Selective and reduce growth of Gram Positive cells? 1. 2. When colonies of cells are pink on DOC agar, what does this indicate about their metabolism? 3a What does the hazy agar around a colony indicate? pincipi-lotich c e bile salt cUtivates gram pos Why is the agar with phenylethyl alcohol considered selective, but not differential media? 4. ? inferyfers co/DNA replicat ian the clestrous membraine e inhibits rom neg bopter io imo dis+ r,'ch, c lin.colly. ?¡gnificant lacteria oso S. Why is blood agar considered both enriched and differential culture media? ment for mand) bacterla i Selec ve eppor the grouth - used to dist ng uish pathagenic bacter iq Describe the 3 types of results that can be observed on blood agar plates, focusing on what is 6. taking place with the red blood cells and how this produces the different results alpha- gren alo beta-CHear holc gamma- na change How can hemolysis benefit a pathogenic bacteria? Selective, Differeatial, and Enriched Media: Reviewl Exercise 12

Explanation / Answer

1. Deoxycholate Agar medium is used for the isolation and growth of intestinal pathogens of Salmonella and Shigella species. The medium inhibits the overgrowth of other micro-flora. The media contains peptone which provides source of carbon, nitrogen, long chain amino acids, vitamins and minerals. Sodium deoxycholate and sodium citrate inhibits the growth of Coliform bacteria and gram-positive bacteria. Sodium chloride in the medium helps to maintain the osmotic balance and dipotassium phosphate buffers the medium. Lactose helps in differentiating enteric bacilli as lactose fermenters produce red colonies while lactose non-fermenters produce colourless colonies.

2.  Coliform bacteria if present in the growth medium forms pink colonies. The degradation of lactose causes acidification of the medium and if the pH < 6.8, the pH indicator Neutral Red will turn pink coloring the colonies pink.

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