I have not had a problem with any of these supplements causing a problem with good bacteria. I have had a problem with coloidal silver, when taken internally, causing a problem, so, I only recommend using it externally, unless there is an emergency and this is all you have on hand. Just to be on the safe side, I did some reseach, and this is what I came up with - taken from the PDR for Herbal Medicines: Oregano Oil - The essential oil, which contains carvacrol, is antimicrobial in vitro. The antibacterial and antifungal activity of oregano is thought to be mainly due to the presence of phenolic compounds such as thymol (11.6%) and carvacrol (3.5%). (Stiles et al. 1995; Biondi et al. 1993) - Antimutagenic and anticarcinogenic properties have been attributed to rosemaric acid isolated from rosemary and oregano (Milic & Milic, 1998). - Essential oil of oregano inhibited Candida albicans growth. Zones of inhibition were similar to that of nystatin (22 to 25 mm). (So, if you're concerned about oregano causing a yeast infection - I think you can rule that out) Calendula - Studies conducted in vitro and in animal models have elicited many potentially useful effects related to compounds present in Calendula officinalis and Calendula arvensis. Among these are anti-inflammatory, antimicrobial, antiviral, and antilipid effects. The flowers are antimicrobial due to the terpene alkaloids, lactone and flavones contained in the essential oil. Flavonoids isolated from flowers of Calendula officianlis demonstrated positive antimicrobial activity against Staphylococcus aureus (at a concentration of 1mg/mL (Dumenil et al., 1980). - Other studies have demonstrated the flavones to be effective against Klebsiella pneumoniae, Sarcina lutea, and Candida monosa. - An infusion made from marigold plants (flowers, leaves, stems) is used to treat hypotension, according to Russian and Ukrainian folk medicine of the Soviet Far East (Moskalenko, 1987). - Organic extracts of the dried flowers of Calendula officinalis exhibited potent anti-HIV activity in an in-vitro MTT/tetrazolium-based assay. (In other words, it is anti-viral) - Calendula is thought to ease gastrointestinal problems by reducing spasms and stimulating the production of bile (Bisset, 1994). - Calendula promotes the formation of granulation tissue, an important step in re-epithelization and healing of wounds (Bisset, 1994). Garlic - Garlic tablets studied in vitro were found to enhance natural killer cells, which are an important part of the immune system in fighting cancers, viruses, and certain bacteria. Antioxidative effects of Garlic, determined by an increase in intracellular glutathione levels, are responsible for decreasing poor cellular function and premature aging. Anitviral activity was also noted in vitro with Garlic tablets (See, 1999). - Studies indicated that Garlic and its components act as a natural antibiotic with broad-spectrum antimicrobial activity against many genaera of bacteria, fungi, and even viruses, including antibiotic-resistant organisms (Farbman et al, 1993; Guo et al, 1993). - Gastrointestinal symptoms, changes to the flora of the intestine, and allergic reactions, including contact dermatitis and asthma (Couturier & Bousquet, 1982), are possible. (So, according to this study - prolonged use of garlic could change the intestinal flora) Grape Seed Extract - Grape Seed extract has shown positive effects against peripheral venous insufficiency, as an antioxidant, in varicose veins, capillary fragility, disorders of the retina including diabetic retinopathy, edema, ocular stress, and premenstrual syndrome. In vitro and animal trials have demonstrated antioxidant, vascular, cytotoxic, chemopreventive, and cytoprotective effects. In addition, the excellent antioxidant effects of Grape Seed extract may offer protection against atherosclerosis and other chronic degenerative diseases, such as cancer. - Grape Seed extract may also support collagen stabilization. - No helath hazards or side effects are known in conjunction with the proper administration of designated therapeutic dosages. Apple Cider Vinegar - Dr. Gabriel Cousins highly recommends sipping 1/3 tsp. of raw apple cider vinegar before meals to activate flow of vital digestive juices, so I can't imagine this would hurt the vital flora or good bacteria. Olive Leaf Extract - Olive leaf extract is used to enhance the immune system, as antimicrobial, as an antioxidant, as a hypoglycemic agent, and in heart disease. - Olive leaf contains flavonoids that possess antioxidant activity, and tissue antioxidant status has been proposed as a key factor in the development of diabetic complications. This may help expelain why an orally administered preparation of olive leaf substantially diminished tissue damage in the kidneys and liver in rats with streptozotoxin-induced diabetes. - The internal administration of the drug can trigger colic among gallstone sufferers, so its use is contraindicated. I hope some of the high-lights of these scientific studies will help you with your decision. It has been my experience that when we work with nature and stay away from the pharmeceuticals, it can only help to bring the body back into balance faster - not cause more problems.