Which prefix is used to indicate a condition that is counter to something else?

The prefix "anti-" is used to indicate a condition that is against or counter to something else. In medical terminology, it is often used in various contexts, such as "antibiotic," which refers to substances that kill or inhibit the growth of bacteria, thereby countering infections. Another example is "antigen," which refers to substances that induce an immune response, opposing the body's normal state.

In contrast, the other prefixes do not convey this meaning. "Pseud/o-" refers to something that is false or not genuine, "macro-" indicates something large or oversized, and "dors/o-" pertains to the back or posterior part of the body. These prefixes represent different concepts that do not involve the idea of countering or opposing a condition.