Question

# Microbiology

My bacteria is serratia marcescens and the test I am working on is nitrate reduction. I believe I would get a positive reaction, but i'm not sure if it would turn red after adding in the reagents or after adding in the zinc?

Answer 1

Bacteria Serratia marcescens is short and the shape is rod in appearence. It's growth is possible during aerobic and anaerobic condition.Being Gram negative it has a cell wall ( thin)covered with outer membrane which consist of lipopolysacchrides. The outer membrane helps to uptake the nutrients.

Identification of Bacteria Serratia marcescens -:

On Nitrate Reduction: it gives positive results with nitrate as it accepts the final electron and not oxygen. Serratia marcescens generally gives red stain.

The bacteria is covered in broth of nitrate and after 4-5 hours if Nitrate is reduced to nitrite and nitrite itself forms nitrous acid. When this nitrous acid reacts with sulfanilic acid gives diazotized sulfanilic acid . It gives red colour on treatment with alpha napthylamine indicating positive results of Nitrate Reduction.

On adding zinc in positive Nitrate Reduction , the red colour will not appear but it gives red colour with other reagent indicating the positive results of Nitrate Reduction.