If you are asking whether some bacteria are parasites, then absolutely yes. I think this is absolutely clear and evident to any and all biologists and would require no discussion. I could expand with some examples, but they would not be very representative of the incredible diversity of parasitic bacteria.
Many bacteria parasitize and live selfishly on hosts. Among them are obligate and facultative parasites. Many become parasitic if there are changes on their host (e.g. think pH in your oral cavity). These are endless. And to expand on this ecological discussion, I think another related and interesting relationship in nature exists which is not technically parasitic but falls into a similar category...
Yet many other bacteria are symbiotic commensals, i.e. do not benefit nor harm the host. As commensals, they have various commensal relationships with the host:
- chemical commensals
(exploit the available chemistry of the host),
where the bacteria will live in the host's prepared environment (think ant hills or termite mounds or bird nests; or sewers, air vents, the list is endless especially for human environments)
(when the aprasite depends on the environment previously prepared by another organism; think how bacteria may parasitize fungi on the ground, which digest dead plant matter; the fungi deploy antibiotics to prevent this kind of parasitism, and we've used these defences for our own medicine... penicillin is from fungi!), and