Hi, Antibiotics do not weaken the resistance to infection but alter the gut flora. Human gut contains various microbes (flora) that are beneficial for human health as well as harmful, especially when they multiply. Normally there is a balance between these two. Broad spectrum antibiotics in addition to killing the invading bacteria causing the infection also suppress the beneficial ( good ) microbes and thus there is overgrowth of harmful microbes such as clostridium difficile which causes abdominal cramps and severe diarrhea. It is found that most of the gut microbes return to normal after four weeks after stopping the antibiotic. Yes, by taking econorm or fermented foods which are natural sources of probiotics will prevent this imbalance. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. Mohammed Taher Ali, General & Family Physician