Are you asking for M.Sc programme? St.Xavier's college(Kolkata) takes the admission through an admission test. As per the eligibility you should be passed B.Sc Major (Honours) in Microbiology or any other
subject of Life sciences with a minimum of 55% marks (45% for reserved category). 

St.Xavier's college(Kolkata) offers Integrated M.Sc Biotechnology programme. You can check its detail with the given below link.

http://www.sxccal.edu/departments/MscBiotechnology/MscBiotechnology.htm

Good Luck!