There isn't really a "purpose" for harmful bacteria, or anything else, in the scientific sense (perhaps what you really meant to ask was "Why did God/the gods create harmful bacteria?" but then you should have put it in the Religion category).
Some bacteria are "harmful" because that helps them spread and reproduce (bacteria that happened to cause coughing or sneezing spread more effectively, and so passed that trait on to their descendants). Some bacteria are harmful as a defense against other kinds of bacteria; a species that can live in a highly toxic environment has at least some incentive to MAKE the environment highly toxic so that they don't have to compete with other species. And some bacteria are harmful more or less "by accident"; they don't derive any real benefit from being harmful, but there's no advantage to them in NOT being harmful either, so there's no evolutionary pressure on them to become either more or less harmful.
Yes. Most bacteria is not harmful to us such as bacteria in a yogurt, but some bacteria is harmful.
Only 1% of bacteria is harmful to humans
not all the bacteria harmful. bacteria that are harmful is i dont know sorry. have a nice DAY!!
Harmful bacteria will harm you. Helpful bacteria will help you.
the harmful bacteria live in air,human body etc.
Bacteria can make you get a harmful diseese, and you could dye. ( I think )
harmful
There are harmful to all organisms, but some bacteria are helpful in many ways.
a bacillus bacteria
Bacteria in storm water can definitely be considered harmful. This is because this bacteria is hard to kill and foreign to your body.
All Microbes are not harmful. All virus are harmful. Some bacteria are harmful
Bacteria can be both harmful and helpful