Colistin resistance genes found lurking on hospital surfaces

The emergence of colistin resistance in antibiotic resistant Gram-negative bacteria like CPE is a real concern. An Italian study just published has discovered colistin-resistance genes (mcr-1) on hospital surfaces. This raises the worrying possibility that hospital surfaces could be an important reservoir from which colistin resistance genes could spread to bacteria that cause healthcare-associated infection, making infections even more difficult to treat.

The study reanalysed a library of 300 Enterobacteriaceae isolates from environmental samples collected from floors, bedrails, and sinks in eight Italian hospitals during 2016-17. Amazingly, 8.3% (25/300) of the Enterobacteriaceae harboured the mcr-1 colistin resistance gene. A wide range of bacterial species were represented among those harbouring mcr-1, including a mixture of environmental bacteria, and those that are a common cause of human infection. The discovery of mcr-1 in K. pneumoniae was most concerning, given the potential for this organism to spread rapidly in healthcare settings.

These findings have probable and important clinical implications. It seems likely that some of the species with mcr-1 identified on hospital surfaces could be transferred to patients – either directly or via the hands of healthcare workers ?? and establish colonisation and/or cause infection. Also, it seems likely that the mcr-1 gene will spread horizontally between bacteria in the environment, providing an active reservoir for the creation of colistin-resistant bacteria that could go on to cause human infection. This issue is made worse by the presence of dry surface biofilms, which provide a protected environment for the sharing of resistance genes.

The presence of the mcr-1 colistin resistance gene on hospital surfaces presents a risk of enhancing the development and spread of colisin-resistant bacteria in hospitals. In the light of these findings, we need to continue to focus on the best ways to reduce the risk associated with the contamination of surfaces with pathogens in the healthcare setting.

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Are surfaces a hidden reservoir for Mycobacterium contamination of heater-cooler units?

There's an emerging global epidemic of Mycobacterium chimaera infections following cardiothoracic surgery associated with contaminated heater-cooler units (machines that are used in theatre during some procedures). It has been established that water within the machines can become contaminated with Mycobacterium species, and that this can create a bio-aerosol that finds its way into the surgical field and causes an infection. However, a recent study from Hong Kong highlights the potential for surfaces on the heater-cooler units to be reservoirs for Mycobacterium.

The study was performed as part of an investigation into a string of cases of Mycobacterium chimaera surgical infections following cardiac valve replacement. The investigation discovered, as with many others around the world, that the water reservoir within the machines was contaminated with M. chimaera before and after disinfection of the water, providing a plausible source for the surgical infections.

However, the authors went further, and performed sampling of the surfaces on the inside and the outside of the heater-cooler units. No contamination of the outside surfaces of the units, which were effectively disinfected using Clinell Universal Wipes, was identified. However, 4/8 (50%) of the inner surfaces of the units were contaminated with M. chimaera. It's possible that this surface contamination could be involved, either directly or indirectly, in seeding the airflow exiting the units that then enters the surgical field and causes a surgical infection. For example, M. chimaera is eliminated successfully from the water reservoir within a unit, contamination of the internal surfaces of the unit could then decontaminate the water reservoir!

This is the first study (that we've come across) exploring surface contamination with M. chimaera in the context of heater-cooler units used for cardiothoracic surgery. The findings certainly raise some important questions and warrant further investigation. It was reassuring that no contamination was identified on the outer surfaces of the units. However, how much of a clinical risk does contamination of the internal surfaces of these units present? How can this be reduced or eliminated? Could vapour-phase decontamination methods such as hydrogen peroxide vapour could play a role? As the global community strives to mitigate the risk of M. chimaera infections associated with heater-cooler units, contamination of surfaces could be a new frontier!

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