Grapefruit seed extract (Citricidal) is extracted using benzalkonium chloride

Benzalkonium chloride is antibacterial and anti fungal and is used topically in medical preparations such as disinfectant wipes and eye drops. It is not to be ingested (as citricidal is) and is toxic in amounts of 8% and over.

In tests it was shown that it is the residue of benzalkonium chloride that has the antimicrobial effect because grapefruit seed extract without the use of benzethonium chloride had no antimicrobial effect.

Check out the Wikipedia and scroll down to Scientific Research

And Terressentials

Are there any other natural antibiotic and anti fungal products?
Yes.
Kyolic Garlic
Tea-tree
Olive Leaf extract
Colloidal silver

Please read the directions on the bottle and take all herbal products with caution. Olive Leaf extract is a vermifuge; that is an agent that causes the expulsion of worms or parasites from the body. This can cause distressing symptoms so take one capsule a day for a few days before increasing the dose. Never take antibiotic/anti fungal products together or in conjunction with prescribed antibiotic/anti fungal medication as one will reduce or increase the efficacy of the other which has the potential for some extreme side-effects and therefore further illness.

REMEMBER THAT YOU SHOULD ALWAYS CONSULT YOUR MEDICAL PRACTITIONER WITH ANY HEALTH CONCERNS