Describe the pathophysiology of acalculous cholecystitis. What are the common organisms involved?
a) Obstruction of cystic duct by gallstones; Escherichia coli
b) Inflammation of the gallbladder without stones; Staphylococcus aureus
c) Gallstone formation; Clostridium difficile
d) Infection of common bile duct; Streptococcus pneumoniae