Natural sources of antimicrobial agents include which of the following?

• A. secretions of fungi, soil bacteria
• B. human tears
• C. synthetic drugs
• D. plant extracts only

Answer: (A)

Natural antimicrobial agents come from organisms that produce these compounds to compete with others. Fungi and soil bacteria are well known for releasing antibiotic substances as part of their normal metabolism. Penicillium gave us penicillin, and Streptomyces and related soil bacteria have yielded many antibiotics still in use today. That makes secretions of fungi and soil bacteria the best representative natural sources of antimicrobial agents. Tears do have antimicrobial components, and plants also contain antimicrobial compounds, but the strongest, most historically important natural sources are the fungi and soil bacteria. Synthetic drugs are manufactured, not natural producers, which is why the full, best answer centers on these natural producers.