Microbiology is not usually considered as a field where you get a degree and secure a job. This subject mostly aims on research, to discover new techniques which could lead to betterment of our daily life. Its vast field can take you to any sectors such as pharmaceuticals, bio-remediation, agriculture, food and beverage industries etc. You can opt for a job in these sectors or can choose academic line where you can do a PhD or post doc. and get a teaching position in any university or can join as a research fellow in one of the various organisations or even in private labs. You can choose medical line where you could be appointed in a diagnostic lab. You will never be able to outrun your career options, being a student of microbiology.

Coming to another part of your query, benefit of doing MSc. Post graduation in any stream will take a student to further depth of knowledge that one can never imagine as an undergraduate student. To emerge successful in your job, you will need to apply your post graduation knowledge every now and then. Here you will be more eligible than other competitors who have applied for the same job position with an undergraduate degree.