James T. Walker

Microbial Biofilm Formation and Contamination of Dental-Unit Water Systems in General Dental Practice

ABSTRACT Dental-unit water systems (DUWS) harbor bacterial biofilms, which may serve as a haven for pathogens. The aim of this study was to investigate the microbial load of water from DUWS in general dental practices and the biofouling of DUWS tubing. Water and tube samples were taken from 55 dental surgeries in southwestern England. Contamination was determined by viable counts on environmentally selective, clinically selective, and pathogen-selective media, and biofouling was determined by using microscopic and image analysis techniques. Microbial loading ranged from 500 to 105CFU · ml−1; in 95% of DUWS water samples, it exceeded European Union drinking water guidelines and in 83% it exceeded American Dental Association DUWS standards. Among visible bacteria, 68% were viable by BacLight staining, but only 5% of this “viable by BacLight” fraction produced colonies on agar plates. Legionella pneumophila,Mycobacterium spp., Candida spp., andPseudomonas spp. were detected in one, five, two, and nine different surgeries, respectively. Presumptive oral streptococci andFusobacterium spp. were detected in four and one surgeries, respectively, suggesting back siphonage and failure of antiretraction devices. Hepatitis B virus was never detected. Decontamination strategies (5 of 55 surgeries) significantly reduced biofilm coverage but significantly increased microbial numbers in the water phase (in both cases, P < 0.05). Microbial loads were not significantly different in DUWS fed with soft, hard, deionized, or distilled water or in different DUWS (main, tank, or bottle fed). Microbiologically, no DUWS can be considered “cleaner” than others. DUWS deliver water to patients with microbial levels exceeding those considered safe for drinking water.

Medical biofilms : detection, prevention, and control

Contributors.Preface.Glossary.1. Microbial Biofilms in Medicine (J, Jass, S. Surman and J. Walker).2. Biofilms Associated with Medical Devices and Implants.Problems of Biofilms Associated with Medical Devices and Implants (R. Donlan).Pathogenesis and Detection of Biofilm Formation, on Medical Impants (C. von Eiff and G. Peters).Control of Biofilms Associated With Implanted Medical Devices (P. Gilbert, et al.).3. Microbial Adhesion and Biofilm Formation on Tissue Surfaces.Biofilm-related Infections on Tissue Surfaces (S. Wai, Y. Mizunoe and J. Jass).Interaction of Biofilms with Tissues (M. Olson, H. Ceri and D. Morck).Control of Microbial Adhesion and Biofilm Formation on Tissue Surfaces (G. Reid, et al.).4. Dental Plaque and Bacterial Colonization of Dental Materials.Dental Plaque and Bacterial Colonization (D. Spratt).Detection of Microorganisms in Dental Plaque (D. Dymock).Control of Dental Plaque (R. Sammons).5. Biofilms Past, Present and Future-New Methods and Control Strategies in Medicine (J. Walker, S. Surman and J. Jass).Index.

Microscopy methods to investigate structure of potable water biofilms.

Publisher Summary This chapter discusses a number of methods used for the visualization of biofilm that has been developed primarily on plumbing tube materials. Differential interference contrast (DIC) and fuorescence microscopy examination was carded out using a Nikon Labophot-2 that combined both epifluorescence and DIC. Photography was carded out using a Nikon F-801 35 mm camera and a JVC TK-1085E color video camera head with built-in compact power source fitted to a trinocular head. Using the video camera, visualization of the subject matter was relayed either to a video monitor for time lapse photography or to the multisync monitor (Taxan) for the image analysis program—both of which increased magnification to greater than 1500 times. A Medical Research Council (MRC)-600 (Bio-pad) fitted with an argon laser with maximum emission at 488 nm and excitation at 514 was mounted in the upright position above an optical light microscope. The images from two different fluorescent markers can be imaged simultaneously using an excitation filter and dichroic mirror to direct the image to either photomultiplier l or 2. These filters could be changed without disrupting the optical alignment of the microscope, thus allowing imaging of a single field of view under different spectral conditions.

Implications for Creutzfeldt-Jakob Disease (CJD) in Dentistry: a Review of Current Knowledge

This review explores our current understanding of the risks of (variant) Creutzfeldt-Jakob disease transmission via dental practice, and whether they merit the rigorous enforcement of improved standards of instrument cleaning and decontamination. The recognition of prions as novel infectious agents in humans has caused significant concern among the public and medical professionals alike. Creutzfeldt-Jakob disease (CJD) in humans has been shown to be transmissible via several routes, including transplantation, contaminated medical products, and via neurosurgery. While the likelihood of transmission via dentistry is undoubtedly very low, this may be amplified considerably by unknown risk factors, such as disease prevalence (particularly in the UK), altered tissue distribution of vCJD, and the failure of decontamination processes to address the inactivation of prions adequately. Since current diagnostic techniques are unable to detect PrPSc in human dental tissues, there is limited evidence for the presence of infectivity. Given these uncertainties, the control of risk by reinforced and improved decontamination practices seems the most appropriate response.

[5] Use of continuous culture bioreactors for the study of pathogens such as Campylobacter jejuni and Escherichia coli O 157 in biofilms

Publisher Summary Bacterial growth is a contentious issue, where a multitude of different modes of growth from individual laboratory species in monoculture to multiple species cohabiting in the environment have to be considered. Decisions have to be made as to which growth phase is to be studied, whether in mono- or multiculture, batch, semicontinuous, or continuous culture, and whether a complex, minimal, or defined medium is used as the growth medium. This chapter focuses on use of continuous culture bioreactors for the study of pathogens such as campylobacterjejuni and escherichia coli O157 in biofilms. In a number of studies, the continuous culture bioreactor has been used because of the flexibility in providing a situation where the planktonic and biofilm phases are cultured together. Further, a standardized inoculum can be supplied to a series of “experimental vessels” in which culture conditions can be carefully controlled and the resultant effects compared. When generating biofilms involving microbial pathogens, health and safety implications arise and in some cases, facilities for operator protection are required. The continuous culture laboratory model bioreactor has also been used in other studies to obtain defined, controlled, and reproducible experimental conditions, particularly with respect to biofilms in the aquatic environment.

[4] Direct biofilm monitoring by a capacitance measurement probe in continuous culture chemostats

Publisher Summary Ideally, methods for monitoring of surface biofilms and biofouling that allow direct on-line and in-line sensors to monitor bacterial accumulation and biofouling of a surface are required. Such technology has the capability to allow downstream data to be collected and remotely assessed so that decisions can be made on the basis of real-time results from the developing biofilm. Thus, process systems could be automated so that an alarm would be signaled when specific measurements are obtained by in-line instrumentation. Many of the sensors and methods automated for on-line biomass determinations rely on optical measuring principles or exploit filtration characteristics, density changes, or dielectric properties of suspended cells, such as capacitance. The device is responsive to viable cells adherent on a surface by measuring the capacitance under an electric field. This system was primarily developed for yeast cell systems; however, it is also able to detect biomass produced by bacterial cells in the form of biofilms on a platinum electrode. This enables on-line monitoring and studying of biofouling within a laboratory model system with the potential to be used in natural systems.

[12] Methods used to assess biofouling of material used in distribution and domestic water systems

Publisher Summary The inner surfaces of water distribution pipes and domestic plumbing pipe systems are potential sites for biofilm development. Microbial cells found as part of a biofilm contribute to the contamination of the water bulk phase, possibly due to sloughing as a result of water shear. This chapter discusses how different grades and different surface finishes of stainless steel could affect the microbiology of biofilms at different water flow rates within potable water systems. A mains water simulation system was designed to investigate the effects of flow rate on the microbiology of biofilms, using stainless steel grades 304 and 316 as the metal substratum. The chapter also discusses methods used to assess biofouling of material used in distribution and domestic water systems. All stainless steel slide surfaces used in the mains water simulation system are cleaned in 70% alcohol for a period of 1 hour prior to use. The whole simulation system is also sterilized with peracetic acid according to recommended procedures supplied by the manufacturers. Biofilms are removed from the slides, with the use of a sterile scalpel, and suspended in 10 ml double distilled water before freeze drying and being weighed.

[29] In vitro modeling of biofouling of dental composite materials

Publisher Summary Dental plaque may become calcified, forming hard deposits called calculus on tooth surfaces. When calculus forms on dental composite materials, it can cause staining that may ultimately result in the need to remove and replace the material. This chapter develops an in vitro model system to include relevant, removable, and replaceable surfaces on which biofilms may develop. The model is subsequently modified further to a two-stage system, in which biofilms are developed in an aerated second-stage vessel. The objective of the chapter is to evaluate the utility of this model system to compare the degree of oral microbial biofilm development on six commercial, light-curing dental composite materials supplied “blind” by ESPE Dental AG. The chapter assesses biofilm formation by several criteria, including qualitative and quantitative viable counts of biofilm bacteria, percentage coverage analysis, and an assessment of the strength of microbial adhesion. The results obtained in the in vitro model system are compared in a preliminary evaluation carried out in vivo at ESPE.

Showering BSL-4 Suits to Remove Biological Contamination

Positive pressure suits are widely used at BSL-4 to protect operators from contact with microbiological agents. As there is the potential for the outside of the suits to become contaminated during use, they must be decontaminated prior to final exit from the high-containment laboratory. Chemical showers are used to remove biological material from suits, and the shower effluent is collected for subsequent treatment by heat or chemicals. The efficacy of showering to clean/remove biological materials from two different BSL-4 suits (ILC Dover and Delta) was studied using Bacillus atrophaeus spores dried directly onto the suit surface as a surrogate contaminant, with a 4 log colony forming unit (cfu) reduction pass criterion required. Initial studies using water alone, without disinfectant, achieved a 1–2 log cfu reduction in the microbial contamination. However, direct scrubbing, using a lightweight brush combined with relatively short cycle times (6 minutes) and low water volumes (<45 L per cycle) achieved an average spore reduction of 3.4 log cfu from the suit. The log cfu reduction was dependent on suit type, position of the contamination on the suit surface, and suit fit. Higher reductions (mean 4.2 log cfu) were achieved with the ILC Dover suit than the Delta suit (mean 3.6 log cfu) when the tests were undertaken using experienced staff who had been matched to the suit size. The study highlights that assumptions cannot be made about the efficacy of shower decontamination systems for BSL-4 facilities and that familiarization with decontamination improves the efficacy of removal of biological material during showering.