Bacterial Infection on Guarianthe aurantiaca?

[Britton Flash]

....or Cattleya for those I may have offended. This brown spotting occured a few days after I sprayed my terrarium with Serenade brand fungicide/bateriacide; I spray this every few weeks as a preventative measure, and it has not caused problems. I have had issues with edema on this plant before, in fact you can see a small pimple in this photo. Watering has been regular(cut back slightly now that temp has dropped a bit) and humidity has dropped; point being, (I think) I have ruled that out. It is not raised at all, and it is not spreading.

The active "ingredient" in this brand is a patented strain of Bacillus subtilis. Are there instances of infection caused by typically-beneficial bacterium?

If anyone has any culture tips for this species I made need them.