Fighting Antimicrobial Resistance with Infection Prevention and Control: hospital drains and Carbapenemase-producing Enterobacterales

© Paz Aranega Bou Model sink system

The Microbiology Society is undertaking a project entitled A Sustainable Future as part of our 75th Anniversary, which aims to highlight the Sustainable Development Goals (SDGs) to our members and empower them to use their research to evidence and impact the goals. Earlier this year, we put a call out to our members to submit case studies in the following three areas: antimicrobial resistance, soil health and the circular economy.

This case study is written by Dr Paz Aranega Bou, who is a water systems microbiologist at Public Health England (PHE) and a member of the Microbiology Society. It focuses on antimicrobial resistance; a naturally occurring process, whereby micro-organisms (bacteria, viruses, fungi and parasites) can change and adapt over time, either by modifying the target of the antimicrobial, or by developing and exchanging resistance genes.

Introduction to the project

Antimicrobial resistance is a threat to economic progress, food security and global health. It is therefore not surprising that a multi-faceted, collaborative approach is required to address this issue. New antimicrobials and vaccines are urgently needed, and existing antimicrobials must be used wisely, through improvements in diagnosis and implementation of antimicrobial stewardship.

Infection prevention and control (IPC) is also a powerful tool to fight antimicrobial resistance. Preventing infections from occurring reduces the use of antimicrobials and limits opportunities for drug-resistant microbes to develop and spread. Some infection prevention and control principles, such as handwashing and water sanitation are well established whilst others remain to be fully evaluated.

What are the challenges/needs that this research addresses?

Healthcare settings are particularly vulnerable environments for the spread of antimicrobial resistant infections, due to several factors including the high use of antimicrobials and the presence of immunocompromised individuals. In hospitals, carbapenem antibiotics have been relied on to treat severe infections such as pneumonia, septicaemia, skin and soft-tissue infections and complicated urinary-tract infections caused by bacteria resistant to several antibiotic classes (multidrug resistant bacteria). However, in recent years, resistance to carbapenems has emerged and spread globally. Of the various mechanisms of resistance, the production of carbapenemases, enzymes capable of breaking down carbapenems and other beta-lactam antibiotics, is of particular concern. The genes that encode for these enzymes are often located on mobile genetic elements, DNA segments that can be exchanged between different bacteria. Bacteria capable of producing carbapenemases include members of the family Enterobacterales, such as the important human pathogens Escherichia coli and Klebsiella pneumoniae. Unfortunately, Carbapenemase-producing Enterobacterlaes (CPE) are becoming increasingly common causes of health care-associated infection worldwide.

During a CPE outbreak, colonised patients (patients that have the bacteria in their gut but do not show signs of infection) are believed to be the main reservoir of CPE, with transmission to other patients occurring through direct or indirect contact. Good adherence to hand hygiene by staff, patients and visitors is key to breaking transmission. However, some outbreak investigations have also identified and/or implicated an environmental source.  

Hospital sinks, waste traps and drains harbour complex microbial communities (biofilms) comprising a diverse range of micro-organisms, including those that are resistant to antibiotics. The biofilm environment protects the bacteria from chemical disinfection and other environmental stresses facilitating bacterial survival and growth. The close proximity of bacteria also facilitates the exchange of antibiotic resistance genes, such as those that encode for carbapenemases. During outbreak investigations, CPE are frequently recovered from hospital sinks which, in some cases are the same, or highly similar to those isolated from the patients. This has raised questions regarding the potential role of the hospital sink. Could sinks be a source of CPE infection?

What findings and solutions were provided by this research?

To address this, a large-scale model sink system was designed and built at PHE Porton Down. The model incorporates 12 sinks of two different designs; rear-draining hand-wash basins and base-draining utility sinks, both of which are commonly found in the hospital environment. Sink waste traps known to be contaminated with CPE, were removed from a hospital setting and installed within the model system. Bacterial communities were studied over time and it soon became clear that, if the bacterial communities were to thrive, regular addition of nutrients was essential. The dispersal of bacteria from the sinks was also investigated. Agar settle plates were placed around the sink and at increasing distances from the sink and the tap operated. Splashes, originating from the sink, were cultured and the bacteria identified. The results from this work, published in the Journal of Hospital Infection, demonstrated that CPE present in a sink and/or drainage system, can be dispersed back into the laboratory (or ward) environment, particularly if the tap is aligned to discharge directly into a contaminated drain and/or when drainage is slow. Contaminated splashes could travel up to one metre from the sink, but mostly landed on surfaces immediately surrounding the sink. We also demonstrated that sink design can minimise or even prevent dispersal, for example when draining efficiently, there was little to no dispersal from rear-draining clinical hand wash basins. Studies using this model system have also shown that CPE can migrate through pipework and colonise previously uncontaminated sinks. In our system, this was likely facilitated by a wastewater backflow event and highlights once more the importance of ensuring good, efficient drainage. 

Splashes on settle plate
© Paz Aranega Bou Splashes on settle plate

This work shows that contaminated sinks might be a source of CPE infection but perhaps more importantly, it identifies interventions that could minimise the risk:

  • Installation of rear-draining sinks.
  • Minimising blockages and addressing them in a timely manner when they occur.
  • Reducing the disposal of nutrients down sinks.
  • Avoiding placing patient care items close to sinks.

The work continues, as these interventions will need to be evaluated in real settings. Not only efficacy but feasibility and cost-effectiveness will need to be taken into consideration. IPC is always evolving and adapting to new challenges. Investing in IPC research in the coming years will help us fight the spread of drug resistant infections.


Aranega-Bou P, George RP, Verlander NQ, Paton S, Bennett A, Moore G. Carbapenem-resistant Enterobacteriaceae dispersal from sinks is linked to drain position and drainage rates in a laboratory model system. The Journal of hospital infection 2019; 102(1): 63-9.

O’Neill J. Tackling drug-resistant infections globally: final report and recommendations; 2016. file/784894/UK_AMR_5_year_national_action_plan.pdf

About the author

Dr Paz Aranega Bou is a water systems microbiologist at Public Health England (PHE) and a member of the Microbiology Society. More information about her work is available here.