This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pharmacology
Which of the following is not an established antimicrobial drug synergism at the clinical level? 
Select and explain. 
A. Amphotericin B and flucytosine in cryptococcal meningitis, B. Carbenicillin and gentamicin in pseudomonal infections, C. Penicillin and tetracycline in bacterial meningitis, D. Trimethoprim and sulfamethoxazole in coliform infections
C: Penicillin and tetracycline in bacterial meningitis
Answer: C: Penicillin and tetracycline in bacterial meningitis 
Explanation: Combination of a bacteriostatic and a bactericidal drug in most cases is antagonistic. Bactericidal drugs act on fast multiplying organisms whereas bacteriostatic drugs inhibit the growth. Here, penicillin is bactericidal whereas tetracyclines are bacteriostatic.