Extended-spectrum β-lactamase-producing bacteria from hospital wastewater pipes: isolation, characterization and biofilm control using common disinfectants

Background: Hospital wastewater systems have been identified as reservoirs for antibiotic-resistant bacteria, with biofilms harbouring extended-spectrum β-lactamase (ESBL)-producing micro-organisms posing significant infection risk. 

Aim: To study the antimicrobial susceptibility and biofilm control of ESBL-producing bacteria from wastewater pipes from a tertiary care teaching hospital in Ireland, which had experienced endemic infection outbreaks caused by ESBL-producing bacteria. 

Methods: Following isolation of ESBL producers on selective agar, antibiotic susceptibility profiles were determined for a number of antibiotics assessed for their ability to form biofilms. Biofilm eradication studies using the commercially available disinfectants bleach, Optizan™, Virkon™ and Clinell™ were performed on selected isolates. 

Findings: ESBL-producing bacteria (N = 39 isolates) showed a high degree of resistance to β-lactams. Biofilm-forming ability ranged from non-adherent to strongly adherent and appeared to be source dependent, suggesting that the characteristics of the pipe environment played an important role in biofilm formation. All disinfectants showed effective biofilm eradication under suggested working conditions. Effectiveness was significantly reduced following reductions in concentration and contact time, with only Clinell™ showing significant biofilm reduction against all isolates at all concentrations and contact times tested. Of the chlorine-based formulations, Optizan™ frequently outperformed bleach at lower concentrations and treatment times. Biofilm eradication was strain dependent, with varying disinfectant response profiles observed from biofilms from different Stenotrophomonas maltophilia isolates. 

Conclusions: This study highlights the high degree of ESBL-producing bacteria recovery from patient-facing hospital wastewater apparatus. Their ability to form resident biofilms and act as potential reservoirs of infection emphasizes the need for rigorous and effective infection control practices.