Question

microbiology help

TOT Zoo Add Page Insert Table Chart Text Shape Media Comment These questions will serve in lieu of a lab report for Exercise 15, 16, and 17 You will find the answer to these questions in the background, procedure, results and interpretation sections of manual Exercise 15, 16, and 17, videos, Actions of Selective and Differential Media Chart, and the Principle/Theory article in homework section.) General Questions 1. What is the purpose (function) of selective media? (How does this test help identify organisms.) 2. What is the purpose (function) of differential media? (How does this test help identify organisms.) Questions about Mannitol Salt Agar (MSA) 3. Would this medium have the function of being selective for Staphylococci aureus, if it did not have sait in it? Why or why not? 4. Why would you not choose MSA to help you differentiate Gram negative organisms? (explain based on the media's selective properties) 5. What is the agent (or chemical) and pH indicator in mannitol salt agar that makes the medium differential? How does that agent and indicator work? 6. On MSA, a) gram negative organisms display no inhibited growth. What notation (symbol) would you use to signify that on the Data About Bacteria chart? b) SE displays growth with no change of media around the growth (stays red). What type of organism is it? c) SA displays growth with yellow media all around it. What type of organism is it d) Both LL and BC display no inhibited growth. Why don't they grow on MSA even though they are gram positive organisms? Questions about Eosin Methylene Blue Agar (EMB) 7. Is EMB media helpful to differentiate a) gram negative or b) gram positive organisms? 8. Name the differential agent included in EMB and describe how it differentiates between the three types of organisms (describe the results/appearance of each type of organism). MacBook Air

Answer 1

1.function of selective media-it is a technique which is used to isolate or identify particular organism ,by the help of this media we can grow certain type of organism to grow and also help to inhibit the growth of other organism .there are several components of selective mdia such as nutrient supply ,energy,required minerals and some buffering agents are also needed.,                                                                                                                                                      2.differential media-this type of technique help to visualize that which species of bacteria species posses some specific biochemical process and which is not .some differential media are blood agar (it identify the bacterial species on behalf of its ability to break down red blood cells).,and MAC(MacConkey Agar )this media is designed to isolate and differentiate enterics based on their ability to female lactose.                                                                             3.no,without salt ,this media is unable to being selective for Staphylococci aureus becauseMSA can only be a selective media due to the presence of sodium chloride if this NaCl is absent in this media ,then it does not function or act like a differentia media ,the concentration of NaCl is 7.5%.                                                                                 4.MSA does not favour the growth of gram negative bacteria because the contain bile salts and crystal violet.some gramnegative bacteria such as pseudomonas aerugiinosa does not grow on MSA because they are not halophilic ,they are salt hating bacteria and these gram negative bacteria does not ferment the mannitol.    5. ph indicator in Mannitol is phenol red and the agent is agar,it is a solidifying agent.salt loving bacteria or gram positive bacteria change the red ph into yellow colour most pathogenic staphylococci such as staphylococcus aureus will ferment mannitol.   6.SE is a gram negative bacteria and SA is gram positive ,,LL and BC is a gram positive bacteria but it acts or posses some property of gram negative bacteria.     7.Eosin methylin blue (EMB) is a selective media for gram negative bacteria ,they are selective for coliforms. 8.EMB is a ddifferential medium for the detection of gram negative enteric bacteria ...the components that make EMB differential-peptones ,lactose,sucrose ,dipotassium phosphate ,eosin and methylene blue dyes.gram negative bacteria that ferment lactose sugar turn colonies into dark purple such as E.coli colonies have a charcterized green covering it is due to rapid fermentation of lactose and production of strong acid