Jaundice or preoperative cholestasis (PC) are typical symptoms of pancreatic masses. Approximately 50% of patients undergo preoperative biliary drainage (PBD) placement. PBD is a common cause of bacterobilia (BB) and is a known surgical site infection risk factor. An adjustment of preoperative antibiotic prophylaxis (PAP) may be reasonable according to the profile of BB. For this, we examined the microbiological findings in routine series of patients. To investigate the incidence and profile of biliary bacterial colonization in patients undergoing pancreatic head resections. In the period from January 2009 to December 2015, 285 consecutive pancreatic head resections were performed. Indications for surgery were malignancy (71%), chronic pancreatitis (18%), and others (11%). A PBD was in 51% and PC was in 42%. The standard PAP was ampicillin/sulbactam. Intraoperatively, a smear was taken from the hepatic duct. An analysis of the isolated species and resistograms was performed. Patients were categorized according to the presence or absence of PC (PC+/PC-) and PBD (PBD+/PBD-) into four groups. Antibiotic efficiency was analyzed for standard PAP and possible alternatives. BB was present in 150 patients (53%). BB was significantly more frequent in PBD+ (n =120) than in PBD- (n = 30), P < 0.01. BB was present both in patients with PC and without PC: (PBD-/PC-: 18%, PBD-/PC+: 30%, PBD+/PC-: 88%, PBD+/PC+: 80%). BB was more frequent in malignancy (56%) than in chronic pancreatitis (45%). PBD, however, was the only independent risk factor in multivariate analysis. In total, 357 pathogens (342 bacteria and 15 fungi) were detected. The five most common groups (n = 256, 74.8%) were Enterococcus spp. (28.4%), Streptococcus spp. (16.9%), Klebsiella spp. (12.6%), Escherichia coli (10.5%), and Enterobacter spp. (6.4%). A polymicrobial BB (PBD+: 77% vs PBD-: 40%, P < 0.01) and a more frequent detection of Enterococcus (P < 0.05) was significantly associated with PBD+. In PBD+, the efficiency of imipenem and piperacillin/tazobactam was significantly higher than that of the standard PAP (P < 0.01). PBD-/PC- and PBD-/PC+ were associated with a low rate of BB, while PBD+ was always associated with a high rate of BB. In PBD+ patients, BB was polymicrobial and more often associated with Enterococcus. In PBD+, the spectrum of potential bacteria may not be covered by standard PAP. A more potent alternative for prophylactic application, however, was not found. ©The Author(s) 2019. Published by Baishideng Publishing Group Inc. All rights reserved.