**Abstract**

Biliary tract infections include cholangitis and cholecystitis. They are associated with high morbidity and mortality in elderly patients with comorbid disease. The most common infecting organisms are Enterobacteriaceae ascending from the gastrointestinal tract, Gram-positive pathogens like Enterococci spp.; the infections are rarely caused by fungi, viruses, and parasites. The prime reason for biliary tract infections is the ascending infection due to the reflux of duodenal contents and also the blood-borne infection or infection spreading through the portal-venous channels. The other predisposing conditions causing biliary tract infections include critical illnesses such as trauma, burns, sepsis, HIV infection, immunosuppression, diabetes, non-biliary surgery, and childbirth. The infection is reduced by β-lactam antibiotics or their derivatives, cephalosporins, carbapenems, fluoroquinolones, etc. Empiric treatment with piperacillin/tazobactam or a cephalosporin with or without metronidazole is recommended for moderate and severe acute cholecystitis irrespective of whether there is growth by culture. Patients with severe cholecystitis are unfortunately difficult to identify properly, both clinically and radiologically, because clinical symptoms are unexpected, and imaging investigations are frequently ambiguous. However, there are significant differences in morbidity and death rates between individuals with mild cholecystitis and those with severe cholecystitis. Preventing related consequences requires early identification and effective therapy of individuals at risk of severe cholecystitis.

**Keywords:** acute cholecystitis, bacteria, chronic cholecystitis, antibiotics, cholangitis
