Final answer:
Trimethoprim is the only bacteriostatic antibiotic among the options given, as it inhibits bacterial folic acid synthesis without directly killing the bacteria.
Step-by-step explanation:
The question asks which of the following is bacteriostatic only. The answer is D. Trimethoprim. Trimethoprim is an antibiotic that inhibits the bacterial enzyme responsible for the production of folic acid, which bacteria require for DNA synthesis, without which they cannot reproduce. This mode of action qualifies it as bacteriostatic since it inhibits the growth and multiplication of bacteria rather than killing them outright.Contrary to trimethoprim, antibiotics like Penicillin, Gentamicin, Vancomycin, and Cefoxitin are typically bactericidal, meaning they kill bacteria directly. Penicillin and its derivatives, as well as cephalosporins like cefoxitin, interfere with cell wall synthesis in bacteria leading to cell lysis and death. Aminoglycosides such as gentamicin disrupt bacterial protein synthesis, which can be lethal to bacteria. Vancomycin, another cell wall synthesis inhibitor, is also bactericidal and is often used to treat serious Gram-positive infections.