I know antibiotics cause c.diff infection. but does clorhexidine gluconate cause c.diff as it kills bacteria? can clorhexidine gluconate gargle cause c.diff or kill good bacteria in the gut?

Unlike antibiotics, antiseptics (like chlorhexidine) generally do not stimulate resistance or increase risk of C diff. Chlorhexidine gargle alters the oral microbiome (the mix of bacteria in the oral cavity) but probably has no major effect on intestinal bactera, at least not in recommended doses. Follow label directions on frequency of use; and spit it out after gargling -- don't swallow it.