I may be way off here, but if you're looking at detecting bacteria by flow, you don't always need antibodies. Indeed, its tricky to get antibodies against bacteria other than the common model species. I haven't been able to find anything. I have used 2-NBDG, DAPI, and SYTO9 before and they work well, depending on your laser sets. These work if all you want to see if bacteria, but if you really need antibodies, I'm sorry.
Here's a reference below:
Berney et al. 2006. Flow-cytometric study of vital cellular functions in
Escherichia coli during solar disinfection (SODIS). Microbiology. 152: 1719-29.
What I have used for bacteria analysis using flow cytometry is LIVE/DEAD BacLight. With this kit I'm able to distinguish live from dead bacteria and it also works different for Gram- and Gram+ bacteria. Attached you can find the protocol.