This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Bacteriology, Subject name: Microbiology
Effective for common gram-negative anaerobes 
Select and explain. 
A. Aztreonam, B. Doxycycline, C. Vancomycin, D. Tobramycin
A: Aztreonam
Answer: A: Aztreonam 
Explanation: Aztreonam is effective for Gram-negative anaerobes like Bacteroides, Porphyromonas, Prevotella. Reference: Textbook of Microbiology; Anathanarayan and paniker&;s; 9th edition; Page no: 269