<prompt> Which of the following drug is active selectively against Anaerobic and Microaerophilic organisms ?ClindamycinTetracyclineMetronidazoleAminoglycosides  <response>: Metronidazole undergoes reduction reaction by receiving single electron from Microaerophilic and Anaerobes pathogens which conves into a highly reactive Nitroradical Anion and damages the pathogen DNA . Metronidazole manifests antibacterial activity against all Anaerobic cocci; Anaerobic gram-negative bacilliincl.Bacteroides sp.; Anaerobic spore-forming gram-positive bacilli such as Clostridium; and Microaerophilic bacteria such as Helicobacter and Campylobacter sp. So Metronidazole is less active against Aerobic organisms because of the lack of Radical-mediated mechanism. Nonsporulating gram-positive bacilli often are resistant, as they are aerobic and facultatively anaerobic bacteria. 