Question

Lob 25 Assays for ldanta 378 Unit 4 | Identifying Medically Significant Bacteria 4. If the only assay you had available was the methyl red assay, would you be able to distinguish E coli from E. oerogenes? Explain your answer 5. What is the value of an uninoculated SIM control tube when you are trying to de- termine if a species is motile or not? 6. Why is it difficult to determine motility in SIM agar) when a species is positive for hydrogen sulfide production? 7. If you just wanted to determine motility for a HaS po change the formula Explain your species, how would you agar to prevent problems with HS production?

Answer 1

4)

• we can distinguise E.coli ans E.aerohenes by using methyl red assay.
• E.coli gives positive methyl red test and E.aerogens gives negative.
• this test detect the ability of bacteria which undergo multi-acid production pathway, which convert medium acidic upto pH 4. E.coli undergoed this pathway, added methyl red indicator turns red coloration inder pH 4. and gives positive result.

5)

• in inoculated tube, if bacteria is motile they radially fade away from their inoculation site and we can observe growth around inoculation site.
• where in control (uninoculated SIM) we cannot observe growth of bacteria in the medium.

6)

• sodium thiosulphate is added in the SIM agar. and H2S producing bacteria utilize sodium thiosulphate which convert the medium black. so that we cannot thus it is difficul to observe whether bacteria is motile or not.

7)

• we just do not add sodium thiosulphate into the medium thus H2S won't be produced and black colour will not be observed. so there would be no difficulty in determining motility of H2S producing bacteria.