Microbiology

Yes, you are eligible to do M.Sc in Nutrition and dietician as you are zoology graduate.
Eligibility Criteria for M.Sc in Nutrition and dietician.
Bachelor's degree (Home Sciences/ Medical/ non-medical/Bio- Sciences) or equivalent or relevant higher qualification.
Almost all the important and reputed colleges offering this course conduct entrance examination.
There are numerous programmes available at the graduate, postgraduate level on Nutrition and dietician.
You are eligible to do Post graduate Diploma or Degree course in Nutrition and dietician.
The M.Sc Food and Nutrition allows you to specialize in one of these areas:
Therapeutic Nutrition
Public Health Nutrition
Food Science
You can choose the course and specialization according to your academics interest and requirement.

I think you have to strictly focus on yours B.Sc Microbiology instead of looking for some short term useful courses. Because these courses can distract you from the original goal. B.Sc. Microbiology is a broad discipline that involves the study of the biology of bacteria, viruses, protozoa and fungi. The main focus of the course is the pathogenic potential of the organisms that cause disease in man. The course also covers aspects of the biochemistry, physiology and genetics of microorganisms. So here are lot more things for learning and innovation. Microbiologists are in demand in medical research, quality control, and the biotechnology industry. Many such graduates secure jobs as researchers working in universities, pharmaceutical and bio Science companies and institutes. Successful graduates of the course also progress into laboratory-based careers in clinical or technical roles which do not involve research. The transferable skills one develops also equip one well for a wide range of careers outside the lab. M.Sc. And Ph.D. are the other options can be set as the target for higher studies.