Anybody doubting that biofilms really do exist on dry hospital surfaces needs to read this study: biofilms are there, they are complex, and they are common. A landmark study by the same Australian Vickery group published in 2012 first identified biofilms on a handful of dry hospital surfaces in an ICU. But this study is far more comprehensive and convincing.
The team cut samples of patient bedding (n = 11), patient surrounds (n = 19), and fixed furnishings (n = 14) from an ICU. Each sample was cultured using a conventional approach, tested for the presence of S. aureus by PCR, examined for the presence of biofilm under electron microscopy, 18 samples underwent a live/dead microscopy technique 12 months after sample collection, and 15 samples were pyrosequenced to evaluate their “environmentome”.
Biofilm was detected on a whopping 41/44 (93%) of the samples. And all 18 of the samples evaluated using live/dead microscopy contained live bacteria 12 months after sample collection. Furthermore, MRSA was cultured from 18%, ESBL from 11% and VRE from 8% of the samples, and 50% of the samples gave a positive signal for S. aureus by PCR.
I’m not certain what the PCR for S. aureus adds to the findings. It’s not possible to say whether this was viable S. aureus or a fragment of DNA detected from dead bacteria. A study that I did years ago suggested that PCR was not a good tool for environmental sampling for MRSA.
The “environmentome” analysis is perhaps the most interesting aspect of the study. As you may expect, the diversity of bacteria identified in the biofilms was broad and environmental organisms that you probably haven’t heard of (even if you’re a microbiologist) predominated. For example, Faecalibacterium prausnitzii and Massilia timonae (had to copy and paste those) were the two most common organisms, followed by S. aureus and coag-neg staph. Perhaps surprisingly the floor biofilms were less diverse than the biofilms from the patient surrounds. The figures (see below) are probably the most meaningful way to interpret the environmentome data, showing that the source of predominating bacteria (gut flora, environmental, skin flora or unknown) varied substantially by sample type, with environmental bacteria dominating mattresses and the floor, and gut / skin flora dominating pillows. (Although best not to think about why gut flora were so common on pillows…) Phylogenetically, there was clustering of the environmentome by specimen location, as you would expect, although the floor was so diverse that floor specimens did not cluster together. One interesting finding was that obligate anaerobes accounted for something like 50% of the bacterial species identified – from open surfaces in the ICU. This suggests that these obligate anaerobes were lurking deep in the anaerobic portions of the biofilms.
Figure: Composition of biofilms by bacterial source.
As if to illustrate the inadequacy of conventional methods in addressing these biofilms, a neat feature of the study was that the samples were collected immediately after two-step cleaning / disinfection, with a detergent clean followed by a bleach disinfection. It is no great surprise that conventional methods do not eliminate biofilms. We know that biofilms provide physical protection from cleaning and also make microbes considerably less susceptible to disinfects by a factor of 10-1000 fold!
So what to do about biofilms on dry hospital surfaces? It seems likely that a daily light clean with existing products will do little more than feed and water these biofilms. We need new products and approaches designed specifically with biofilms in mind. But more importantly, the world needs to wake up to the fact that biofilms are present on dry hospital surfaces, and that this is a problem we need to address. No more can we consider the hospital environment (or any other environment for that matter) ‘inanimate’. It couldn’t be more ‘animate’. More animate in fact than our own bodies in terms of number of living cells!
Image credit: Anthony D’Onofrio.
