Abstract: Objective To investigate the causes of recurrent bloodstream infections by Bacillus cereus in maintenance hemodialysis patients in the First People's Hospital of Longquanyi District Chengdu, and to explore the biofilm-forming ability of the isolates and the importance of preventing nosocomial infection.  Methods A total of 15 strains of Bacillus cereus including 11 clinical and 4 environmental strains were collected. Bacterial identification, antimicrobial susceptibility test and biofilm formation experiments were conducted. Three clinical strains selected at the clinical stage of different antibiotic therapies and 3 environmental strains were subjected to phylogenetic analysis and biofilm formation-associated genes detection.  Results All the 15 strains were identified as Bacillus cereus by matrix assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF MS). Antimicrobial susceptibility test showed that all of the clinical strains (11/11, 100%) were sensitive to levofloxacin, meropenem, erythromycin, rifampicin, tetracycline and vancomycin and resistant to penicillin, 63.6% (7/11) were resistant to cotrimoxazole, and 72.7% (8/11) were intermediately resistant to clindamycin. Three of the clinical strains phylogenetically resemble the strains isolated from hands of the staff working in the blood purification room, and carried 7 biofilm-forming genes, including calY, cdgD, cdgF, sinl, sinR, spoOA and tasA. Biofilm-forming ability was found in 9 (81.8%) of the 11 clinical strains, and this ability could be transiently inhibited in the presence of moxifloxacin or vancomycin.  Conclusions Bacillus cereus can cause catheter-associated bloodstream infection in hemodialysis patients. The formation of biofilm causes the difficulties to eradicate the infection. Hand hygiene should be emphasized to avoid nosocomial infection.

Key words:  Bacillus cereus, Biofilm, Hemodialysis, Nosocomial infection, Hand hygiene