Question

Micro the unknown report

Help! My unknown is gram+ cocci, endospore-forming, and then I went to the nitrate test. I added 5 drops for both reagent A&B first and it didn't turn red but something like light orange. Then I add the Zine. It turned red which below the powder but not the whole tube turn red.. Then I mixed them together. the red is gone and the tube become grey which is the powder's color. SO does it mean it's nitrate - or +.I am confuse because i google what should the "red" look like in this test and it's kind of different. HElP because it will directly affect my result.Sporosarcina ureae or Sporosarcina halophila. OR what other test should I do to identify the unknown

Answer 1

1. Basically, the words that are stated above indicates the Nitrate reduction test used for determination and differentiation of Enterobacteria which basically comprises of gram-negative bacteria. Whereas, the species mentioned above namely Sporosarcina ureae is a gram-positive Cocci. So, technically the result for Nitrate reduction test should be negative.
2. Enterobacteria basically has enzymes that convert nitrate to nitrite which in turn simultaneously gets converted to form Nitrous acid. In the next step, sulphaniclic acid is formed which reacts with Nitrous acid to form a red coloured complex. If this complex is not formed as stated above as orange colour, the results are negative. In the case mentioned above, an orange coloured complex is formed indicating that the bacteria lack the enzyme for conversion of nitrate to nitrite and hence they cannot form a red coloured complex.
3. In the next step for further confirmation, zinc is added which reacts with unreduced nitrate to form a red coloured complex. However, if zinc does not form red coloured complex, nitrites have been further reduced. So, it indicates that formation of red complex after reaction with zinc is a negative test result for Nitrate reduction test. This implies that the bacteria does not belong to Enterobacteriaceae. So, the bacteria should basically be a gram-positive bacteria.