https://scholarworks.montana.edu/xmlui/bitstream/handle/1/11518/15-002_Surface-attached_cells_biofilms_A1b.pdf;jsessionid=74008481C9803976B304DF3CB83E19C2?sequence=1
Surface-attached cells, biofilms and biocide susceptibility: Implications for hospital cleaning and disinfection
Authors: J.A. Otter, K. Vickery, J.T. Walker, E. deLancey Pulcini, P. Stoodley, S.D. Goldenberg, J.A.G. Salkeld, J. Chewins, S. Yezli, & J.D. Edgeworth
Summary
Microbes tend to attach to available surfaces and readily form biofilms, which is prob-lematic in healthcare settings. Biofilms are traditionally associated with wet or damp surfaces such as indwelling medical devices and tubing on medical equipment. However, microbes can survive for extended periods in a desiccated state on dry hospital surfaces, and biofilms have recently been discovered on dry hospital surfaces. Microbes attached to surfaces and in biofilms are less susceptible to biocides, antibiotics and physical stress. Thus, surface attachment and/or biofilm formation may explain how vegetative bacteria can survive on surfaces for weeks to months (or more), interfere with attempts to recover microbes through environmental sampling, and provide a mixed bacterial population for the horizontal transfer of resistance genes.
The capacity of existing detergent formulations and disinfectants to disrupt biofilms may have an important and previously unrecognized role in determining their effectiveness in the field, which should be reflected in testing standards. There is a need for further research to elucidate the nature and physiology of microbes on dry hospital surfaces, specifically the prevalence and composition of biofilms. This will inform new approaches to hospital cleaning and disinfection, including novel surfaces that reduce microbial attachment and improve microbial detachment, and methods to augment the activity of biocides against surface-attached microbes such as bacteriophages and antimicrobial peptides. Future strategies to address environmental contamination on hospital surfaces should consider the presence of microbes attached to surfaces, including biofilms.
Introduction
Microbes tend to attach to available surfaces and form biofilms readily.1e3 Biofilms are problematic in healthcare settings, where they are thought to be involved in 65% of nosocomial infections, and are usually reported in relation to indwelling medical devices and prostheses, water lines and tubing on endoscopes, and on wounds.
In these settings, biofilm persistence can be prolonged, periodically ‘sloughing off’ and releasing planktonic bacteria that may act as a source of infection. Biofilms are a common problem on liquidehard surface interfaces, and in areas of a hospital that are usually wet or damp, such as taps and sink drains.
The recent problems caused by Pseudomonas aeruginosa in water supplied to intensive care units, which resulted in changes to UK national guidance, illustrates this problem. A biofilm is a community of micro-organisms attached to a substrate producing extracellular polymeric substances (EPS) and exhibiting an altered phenotype compared with corresponding planktonic cells, especially regarding growth, gene transcription, protein production and intercellular interaction.
Biofilms comprising various micro-organisms, including bacteria, viruses, fungi and other micro-organisms, can form on almost any biological or inanimate surface, and have been identified in various industrial and clinical settings.
Not all microbes attached to surfaces meet the definition of a biofilm, and the transition from a planktonic culture through surface attachment to an established biofilm is likely to be a continuum rather than a stepwise process (Figure 1).
Microbes including bacterial spores, vegetative bacteria, fungi and viruses can also survive on dry surfaces for extended periods.8e10 Contaminated environmental surfaces are an increasingly recognized reservoir in the transmission of certain healthcare-associated pathogens.
Whilst this extende survival is not surprising for the metabolically inert bacterial endospores, survival of some vegetative bacteria that is measured in years rather than days challenges our understanding of bacterial physiology.
The structural and physiological state of microbes dried on to hospital surfaces has not been studied in detail, but it seems likely that bacteria attach to surfaces to some degree, and may form biofilms. Indeed, a recent study from Australia by Vickery et al.15 ‘destructively sampled’ (i.e. cut the materials out of the hospital environment and undertook laboratory analysis) several hospital surfaces after cleaning and bleach disinfection.
Scanning electron microscopy was used to examine the surfaces for biofilms, which were identified on five of six surfaces. Furthermore, viable meticillin-resistant Staphylococcus aureus (MRSA) was identified in the biofilm on three of the surfaces. This article will review in-vitro studies that explore the structure, physiology and biocide susceptibility of microbes dried on to hard surfaces in the context of surface attachment and biofilm establishment, and discuss the potential implications for hospital cleaning and disinfection.
Conclusion
Surface-attached cells are likely to be common on dry hospital surfaces, and there is evidence that they also harbour established biofilms. The variety of methods used to create and evaluate in-vitro biofilms makes it difficult to compare studies evaluating antibiofilm biocide activity. Nonetheless, microbes attached to surfaces, especially established biofilms, are less susceptible to chemical biocides, UV radiation and antibiotics than their corresponding planktonic bacteria.
The phase of the surface-attached microbes influences susceptibility: attached cells are more susceptible to biocides than established biofilms; low-density, nutrient-limited biofilms make less of an impact on biocide susceptibility than high-density, highnutrient biofilms; and biocides are less effective for inactivating bacteria in mixed-species biofilms than in single-species biofilms. Biocide-specific issues also influence susceptibility in terms of activity against bacteria in biofilms, and the prevention, promotion and dismantling of biofilms. Reduced susceptibility to biocides combined with protection from physical removal through cleaning is likely to contribute to failures in hospital cleaning and disinfection.
Biofilms may explain why vegetative bacteria can survive for unusually long periods (weeks to months) on dry hospital surfaces. Also, the presence of surface-attached bacteria and biofilms is likely to interfere with attempts to recover bacteria from hospital surfaces, and may lead to underestimation of both the prevalence of contamination with pathogens and the number of bacteria that are on surfaces. This has important implications, particularly for hospital outbreak investigation. Biofilms provide a mixed bacterial community where the horizontal transfer of resistance genes may occur.
Attempts to tackle surfaceattached microbes and biofilms on hospital surfaces should include: identification and selection of biocide and detergents with the best all-round performance, including the ability to inactivate surface-attached cells and biofilms; ensuring that invitro tests are developed to model surface-attached microbes likely to be encountered in the field; harnessing surface science to develop a hospital environment that reduces the chance of biofilm formation; and further research to develop novel approaches to augment the activity of biocides against surface attached microbes, including established biofilms.
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