Final answer:
Clostridium difficile, an anaerobe of the GIT associated with IUD use, causes chronic diarrhea especially after antibiotic use, and is often treated with metronidazole.
Step-by-step explanation:
The anaerobe of the GIT that is associated with IUD use is Clostridium difficile. This bacterium can cause severe gastric problems, especially chronic diarrhea, after the normal gut microflora is eradicated by antibiotics. Treatment of this infection with more antibiotics can exacerbate the problem. However, it has been shown that antibiotic-associated diarrhea caused by C. difficile is often effectively treated with metronidazole. Fecal transplants from healthy donors have also been successfully used to reestablish the normal intestinal microbial community in cases where antibiotic treatment has disrupted the natural balance of the gut microbiome. This strategy is currently being evaluated in clinical trials to ensure safety and effectiveness.