There are antibacterial products available to large producers for use against things like fireblight in orchards. I am not aware of any of these for the retail market, or whether it would even be effective against bacterial diseases of plants in general. They are applied topically but many bacterial plant diseases go systemic rapidly and it would prove to be ineffective anyway.

Just like in medicine, plant pathogens can develop mutations leading to resistance when antibiotics are used over a time period. I do know that recently permission was denied for a new antibiotic to be released for plant use because of the superbugs emerging from overuse of antibiotics.

Cankers are both fungal OR bacterial in origin.

It's brown rose canker, so I am thinking of using sulfur spray, but I am unsure of what kind. There are many choices. I wish I knew if it was fungal or bacteria.

Some bacteria can be harmful to plants, but like us the plants need a wide variety of bacteria to live as well as protect tehm from disease pathogens. Sometimes spraying an antibacterial around the garden can reduce plants ability to fight off attacks from those disease pathogens.
If sulfur is to be sprayed then you need a wettable sulfur powder.

Here is a link that might be useful: About Sulfur

Brown rose canker is caused by the fungi Cryptosporella umbrina. Please do a little bit of research so that you can verify that this is what your roses have. If so, sulfur applications can help prevent the spread of the disease, but cannot cure the cankers.

You should also prune out the diseased tissues, sterilizing your tools and gloves between each cut. Purchase resistant varieties that appear to be injury free. Prevention, selection, and good 'housekeeping ' go hand in hand with your sulfur treatments.

There is a great deal of information about brown rose canker on the internet...I'm sure that your local extension office can help, too.

I have already done that, I was just wondering about antibacterial agents for plants which is not the same as antibiotics. It is funny how there is no information on that subject. I did find lots of stuff in general, but nothing about neosporin type things for plants. Maybe one could put neosporin on the cut of the plants after pruning?

If you are talking neosporin, then you are indeed talking about antibiotics. It's an antibacterial agent as well. Just a specific one. That's why I led you in that direction because streptomycin is widely used in the orchard business, as is oxytetracycline. The reason you can't find anything on antibiotics in agriculture is that they are in the domain of commercial agriculture, and for a very good reason.

OK........did a little plunking around, because I used to use a greenhouse sanitiser called Green Shield, and that was a quaternary ammonium compound. Very pleasant but not labeled for use on plants. I know one of them is and I had to find out which one. This would be an antibacterial compound but not classified as an antibiotic. So, they do exist. It's called Physan 20� and is labeled in a dilute state for plant sanitation. So, they do exist but have no idea if on any less than a professional level. It is also a quaternary ammonium compound and useful for not only bacterial, but fungal, viral and algal pathogens. However, like rhizo says, doubt it would be of use in any type of 'cure' situation. It's a preventative measure and must be used exactly as the label indicates.

Here is a link that might be useful: Physan

I really think you are heading in the wrong direction (think appropriate plant for the appropriate site) if you need first aid to keep something growing well, that's not what gardening is about for me at least, but

Physan 20:

Roses - Brown Canker
Use regular spraying. Application should begin in early Spring as soon as new growth starts and should be made often enough to provide protection throughout the rainy periods and to keep the new growth covered. On the average, an application once a week will be needed from early Spring until plants are dormant.

My note: I'd replace the roses with something less demanding before I'd commit to a continuous weekly spray to keep them healthy. If yours began budding (growth buds) in February like here, you are already about 4 months late, or approximately 16 treatments, in beginning a spray program.

thanks for the Physan 20. I had already discarded those roses that had brown rose canker, but this would be good for tools, and I have algae on my camellias and rhododendrons. I posted about that years ago, but no one ever thought of this idea. I may use a general application to the area that had the roses that had the canker.