Streptomycin or penicillin/streptomycin, and potentially amphotericin B. If you need a penicillin-free alternative, gentamycin is a good option.
I think streptomycin is a good candidate with a broad enough spectrum to target Gram positive, negative and yeasts. You can buy from Thermo Fisher a 1000X penicillin/streptomycin cocktail that you simply add at 1X to your medium, and the spectrum is broader. Due to penicillin allergy, you may need to find an alternative. Gibco markets gentamycin in 10mg/mL and 50mg/mL formats, but I think with gentamycin you definitely want to add amphotericin B. Use the same cocktail across all three types of control.
You can even go as far as to test your antibiotic cocktail in advance, in triplicate on your strains of interest, to ensure you have a valid positive control.
I find these compounds to be quite common and so there are other anti-fungals you could use, but I can't attest to their efficacy.