We all know the issues with antibiotic resistance: no matter how quickly we develop new antibiotics, resistance develops and the antibiotics are no longer useful clinically. Biocides are different, as outlined in a recent review paper: resistance is slower to develop, more subtle, and usually less important clinically. But it does happen – more with some biocides than with others. Therefore, we need to think carefully about the formulation and usage of biocides to minimise the development of biocide resistance.
The review, by Dr Lucy Bock from PHE, began with one of the pioneers of anti-infective research: Joseph Lister. Long before antibiotics came on the scene, Joseph Lister demonstrated that infectious diseases could be treated and prevented using biocides (in his case, carbolic acid). Biocides are commonly used in medicine to sanitise the skin of patients (e.g. before the insertion of vascular catheters or before surgical procedures) and for surface disinfection. We also need to think carefully and commission research to understand where biocides can be used for the treatment and prevention of infection in areas of medicine occupied historically by antibiotics (e.g. wound infections).
The review covers the various ways in which reduced susceptibility to biocides has been reported. Some microbes are intrinsically resistant to some biocides, and for other microbes, adaptive resistance or reduced susceptibility can develop or be acquired. Also, the physiological state of a microbe is an important factor, with microbes encased in biofilms tens to thousands of times less susceptible than microbes that are not in a biofilm.
The clinical implications of reduced biocide susceptibility can be difficult to determine. This is because the level of reduced susceptibility of microbes to biocides is mostly fairly low level, and also adaptive reduced susceptibility to biocides is usually reversible, and reverts when the selective pressure of the biocide is removed (unlike most mechanisms of antibiotic resistance). However, there are some examples of clinically important biocide resistance, for example reduced susceptibility to chlorhexidine. Therefore, steps should be taken to minimise the conditions in which reduced susceptibility to biocides can emerge by using an appropriate biocide, ensure that pre-cleaning is performed to a high standard (to remove organic matter), favouring combination therapy (using biocides with multiple active ingredients), developing anti-biofilm biocide solutions, and developing formulations of disinfectants that reduce the risk of biocide reduced susceptibility.
The impact of an environmental hygiene intervention in reducing the spread of viruses in an office building
Have you suspected your office colleague in giving you that cold? Well, this study suggests that sometimes, you might be right, and that a hygiene intervention including the use of hand sanitising wipes can help to reduce the changes of virus spread in an office setting.
The study was performed in an office building in which around 100 people were working. Two different hygiene-based interventions were tested: the first based on disinfection of surfaces, and the second based on disinfection of both surfaces and office worker hands (using either alcohol hand gel, or hand sanitising wipes). One door hand and an offer worker’s hands were seeded with tracer bacteriophage, which is an effective way of modelling the spread of infectious virus without putting anybody at risk of infection.
From a single point of environmental and human hand inoculation, the bacteriophage tracer spread far and wide, contaminating surfaces and office worker hands throughout the office building. The environmental surface disinfection intervention resulted in a 42% reduction in phage contamination, which was not statistically significant. The intervention that included both environmental surface disinfection and hand disinfection resulted in a statistically significant 85% reduction in bacteriophage contamination.
This study shows that a hygiene intervention targeting both surfaces and the hands of office workers resulted in a significant reduction in viral contamination in an office building setting. These findings are likely to translate into reduced spread of viral illness – making it less likely that you colleague will give you that cold!
The last thing you need if you require the services of an emergency ambulance is exposure to antibiotic-resistant bacteria from contaminated surfaces. A recent US study suggests that this is commonplace, finding MRSA environmental contamination in every single emergency ambulance tested! These findings reinforce the need for thorough cleaning and disinfection of emergency ambulances.
The study team sampled oxygen cylinders and regulators in 9 emergency ambulances, and 70 oxygen cylinders in an off-site storage facility for MRSA. Amazingly, all 9 emergency ambulances were found to be contaminated with MRSA, as were 67/70 (96%) of oxygen cylinders in the storage area. MRSA wasn’t found on most of the surfaces sampled in the ambulance.
The findings are consistent with previous studies, which have also found contamination of ambulances. Furthermore, previous studies have also shown that existing methods for cleaning and disinfecting ambulances are not sufficient to tackle contamination with clinically-relevant organisms. These studies suggest that more needs to be done to ensure that ambulances don’t become a source for the acquisition of MRSA and other antibiotic-resistant bacteria.
The disinfection of ambulances is challenging. They have multiple touch points, a risk of heavy levels of organic soiling, the need for rapid turnaround, and a requirement for environmental hygiene procedures that can be applied quickly and effectively on the road. Disinfectant wipes can help in developing effective environmental hygiene protocols for ambulances.
There is increasing evidence that sink drains can be contaminated with CPE and that this environmental contamination can find its way onto patients. A new study from the US found that contamination of sink drains with CPE and with carbapenemases was commonplace, and that proximity to toilets was an important predictor of drain contamination.
The study was performed in a 26-bed medical ICU within a 600-bed hospital in Milwaukee, Wisconsin. Each room has two sinks and one toilet – one of the sinks is closer to the toilet than the . Each sink drain was sampled using swabs. The KPC carbapenemase gene was detected by direct PCR from more than half of the sinks (54% of 46 sinks), and CPE was cultured from 10% of 40 sinks. The sinks that were closest to the toilet were significantly more likely to be contaminated with the KPC carbapenemase (87% of 23 sinks near toilets vs. 22% of 23 sinks at room entry). The CPE that were cultured from the sinks were a mixture of Enterobacteriacae that are often implicated in human colonisation (such as Klebsiella pneumoniae) and ‘weird and wonderful’ Enterobacteriaceae from the environment.
In this study, the reason why sinks closer to toilets were more contaminated with carbapenemases is not clear. However, it seems likely that differences in the uses of the two sinks in the room explains the difference. The sink at the point of entry into the room would most likely be used by staff either before or after patient care. However, the sink by the toilet would most likely be used by patients following toilet use, and by staff during patient care; and these activities carry a higher risk of contamination being transferred to the sink.
The study underlines the need to improve the management of sinks to ensure that they do not become contaminated with CPE, because we know from other studies that sinks contaminated with CPE are a risk to patients.
Candida auris is a high-profile emerging pathogen, which has caused large outbreaks both in the UK and elsewhere. C. auris can causes widespread environmental contamination, and isn’t susceptible to all disinfectants. This new study from Cardiff University extends previous findings by developing a dry surface biofilm efficacy testing model for C. auris. Worryingly, half of the disinfectants tested barely touched the C. auris in the DSB, suggesting that more powerful disinfectants (such as peracetic acid and sodium hypochlorite) should be selected for dealing with C. auris.
Previous studies have shown that a range of disinfectants are effective against C. auris when using conventional suspension testing methodology. However, we know from other studies that the presence of dry surface biofilm (DSB) can reduce the susceptibility of micro-organisms to disinfectants considerably. DSB occur when bacteria and other microbes become attached to surfaces and encased in a protective ‘slime’ layer: this can reduce their susceptibility to disinfectants by 10 to 1000-fold. Therefore, a team at Cardiff University developed a DSB model for C. auris disinfectant testing. 12 commercially-available wipe based disinfectants were tested. Concerning, 50% of the products tested failed to decrease C. auris viability, 58% failed to prevent its transferability, and 75% did not delay biofilm regrowth. Wipes that were effective in reducing C. auris viability and transferability included Clinell’s Universal Wipes, and Clinell’s Sporicidal Wipes (which are based on peracetic acid). Clinell’s Sporicidal Wipes were most effective at preventing re-growth of the biofilm.
This research reinforces that microbes in DSB are considerably less susceptible to disinfectants than microbes in suspension. Caution should be exercised in choosing the appropriate disinfectants for dealing with surfaces potentially contaminated with C. auris, with decisions informed by studies using DSB-based testing methods.