The correct answer is option 4: Live microbial food supplement.

Probiotics are living microorganisms that are beneficial for our health when consumed in adequate amounts. They are often referred to as "good bacteria" as they help maintain a healthy balance of microbes in our digestive system.

Option 1 (Organic food) is not correct because organic food refers to a method of farming and does not necessarily mean that it contains live microorganisms.

Option 2 (Antacid) is not correct because antacids are medications used to neutralize stomach acid and relieve heartburn or indigestion. They do not contain live microorganisms.

Option 3 (Antibiotic) is not correct because antibiotics are medications used to treat bacterial infections, they are designed to kill or inhibit the growth of bacteria. They do not contain live microorganisms.

Therefore, the correct answer is option 4, as probiotics are specifically defined as live microbial food supplements.