Question

Q14. In the lab info it says that as a rule, most microbes can adjust to a range of salt concentrations. 7/29/2019 Which cell structure allows microbes to physically withstand hypotonic environments? Cell wall MSA has two properties. It is both selective and differential. When bacteria grow on this media, there is a visible difference between bacteria that ferment mannitol, and the bacteria that do not See Figure 2 (a)-effects of selective/differential media. Q15. Which of the following is correct about MSA? a) Species of Staphlycoccus grow on this medium and some produce a yellow halo indicating they ferment mannitol b) Species of Staphlycoccus grow on this medium and all produce a yellow halo since they ferment mannitol c) The pH indicator phenol red turns yellow when the pH increases d) E. coli grows very well on this medium and will appear pinkish/red since it ferments lactose In addition to solutes other chemicals are used to affect the growth of bacteria. One example is phenylethyl alcohol which affects certain bacterial cell walls and can be used to make a selective medium. Look at Figure 1 which shows how E. coli and S.aureus grow on phenylethyl alcohol (PEA) agar compared to nutrient agar. Q16. T/F PEA shows a complete inhibition of the growth of E.coli Eosin-methylene blue agar (EMB) contains compounds that partially inhibit gram positive organisms AND allow a difference to be seen for the bacteria that do grow. FYI, the book shows only one bacterium growing on an EMB plate. 217. T/F Escherichia coli and Enterobacter aerogenes colonies will look the same on EMB, you will wat he able to tell them anart

Answer 1

15. MSA agar supports luxurious growth of Staphylococcus species. The coagulase positiive staph can form yellow halo and coagulase staph give red color. E. coli cannot grow on MSA. The media is red in color which turns to yellow when pH decreases ( becomes acidic). Hence the correct statement is option A.

16. PED inhibits E. coli, as well as most of gram negative bacteria. so its true statement.

17. EMB agar growth of these bacteria: E. coli - good purplish or greenish or blackish growth (with or without a metallic sheen),
Enterbacter aerogenes - good pink or purplish growth,
So the statement is false.

18. Hemolysis are of 3 types;
Alpha - Greenish and partial discoloration of blood agar plate
Beta - clear discoloration, complete breakdown of hemoglobin of blood
gamma - no or very less hemolysis.
SO the ans is option b., beta

19 and 20: These two questions refer to some list given in the question , which is not provided here.
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