Final answer:
Sulfa drugs inhibit bacterial growth by blocking the enzyme involved in folic acid synthesis in bacteria, leading to a halt in nucleic acid production and prevention of bacterial proliferation. These drugs are selectively toxic to bacteria as humans do not synthesize their own folic acid. Sulfanilamide was one of the first of these drugs and remains in use despite common allergic reactions.
Step-by-step explanation:
Sulfa drugs, also known as sulfonamides, inhibit microbial growth by functioning as antimetabolites that interfere with the bacterial synthesis of folic acid. As structural analogs and competitive antagonists of para-aminobenzoic acid (PABA), they bind to the enzyme sulfihydropteroate synthase and prevent the conversion of PABA into dihydrofolic acid, an essential precursor for folic acid. Humans are not affected by this mechanism, as they obtain folic acid through their diet rather than synthesizing it themselves, making sulfonamides selectively toxic to bacteria.
However, sensitivity to sulfa drugs varies among microorganisms; those that need to synthesize their own folic acid are affected by sulfa drugs, whereas those that can use preformed folic acid are unaffected. The deficiency of folic acid synthesis in sensitive bacteria leads to a reduced production of pyrimidines and purines, crucial for nucleic acid synthesis, and results in bacteriostatic inhibition of growth. Sulfa drugs, such as sulfanilamide, were some of the first synthetic antimicrobial agents developed and are still used to treat a variety of bacterial infections, although allergic reactions to these drugs are common.