Integrated M.Sc is nothing but doing M.Sc in the same institute with the continuation of your B.Sc. Sometimes the time duration is less (B.Sc + M.Sc 4 years). Indian Institute of Science is offering Integrated M.Sc programs in science subjects. The facility is that you don’t have to adapt a new environment in a new Institution, the overall time period is less, the syllabus also remains different and made keeping an eye on the long-term involvement of the student. University of Hyderabad is offering the course that you are looking for. You can pursue Integrated M.Sc. Mathematics and Computers after Intermediate. IIT Kharagpur also offering this course and admission will be through IIT JEE Examination.
M.Sc. Medical Microbiology after B.Sc.: Medical microbiology is a good subject but the reality in India is jobs are very limited. Any degree wise also Biochemistry, genetics, biotechnology, microbiology (any branch) are considered as more or less same. You can seek placements with a degree in medical microbiology in the clinical sectors. It is quite supportive work to a pathologist. If you are looking for longtime commitment (5-10 years), then you can move towards research. Clinical microbiology is having quite demanding research areas.
PG in Environmental Science after B.Sc: In govt. sectors like PCB (Pollution control board) and other equivalent organization jobs are there but in private sector it is less. Ministry of Environment and Forests, Government of India is also providing many jobs through ENVIS (Environmental Information System) centers across the country. You can get many details from www.envis.nic.in .