Question

To determine whether the bacteria is gram + or gram - , a girl stain the bacteria with gram liquid and washed it with alcohol . So why she used alcohol , what is the role alcohol in this experiment

Answer 1

in gram -ve bacteria cell wall is mainly consists of glycolipid . so when alcohol is used to wash the bacteria the lipid in the cellwall gets solubilised in the alcohol . so it fails to hold the gram stain. but in gram +ve bacteria cell wall is mainly consists of peptidoglycan, it can hold the stain 
Thus alcohol is used to differentiate the gram +ve & gram -ve bacteria .