186,730 research outputs found
Environmental and genetic factors influencing biofilm structure
No full textIt is increasingly evident that biofilms growing in a diverse range of medical, industrial, and natural environments form a similarly diverse range of complex structures (Stoodley et al., 1999a). These structures often contain water channels which can increase the supply of nutrients to cells in the biofilm (deBeer and Stoodley 1995) and prompted Costerton et al., (1995) to propose that the water channels may serve as a rudimentary circulatory system of benefit to the biofilm as a whole. This concept suggests that biofilm structure may be controlled, to some extent, by the organisms themselves and may be optimized for a certain set of environmental conditions. To date most of the research on biofilm structure has been focused on the influence of external environmental factors such as surface chemistry and roughness, physical forces (i.e. hydrodynamic shear), or nutrient conditions and the chemistry of the aqueous environment. However, there has been a recent increase in the number of researchers using molecular techniques to study the genetic regulation of biofilm formation and development. Davies et al. (1998) demonstrated that the structure of a Pseudomonas aeruginosa biofilm could be controlled through production of the cell signal (or pheromone) N-(3-oxododecanoyl)-L-homoserine lactone (OdDHL). In this paper we will examine some of the research that has been conducted in our labs and the labs of others on the relative contribution of hydrodynamics, nutrients and cell signalling to the structure and behaviour of bacterial biofilms
Influence of hydrodynamics and nutrients on biofilm structure
No full textHydrodynamic conditions control two interlinked parameters; mass transfer and drag, and will, therefore, significantly influence many of the processes involved in biofilm development. The goal of this research was to determine the effect of flow velocity and nutrients on biofilm structure. Biofilms were grown in square glass capillary flow cells under laminar and turbulent flows. Biofilms were observed microscopically under flow conditions using image analysis. Mixed species bacterial biofilms were grown with glucose (40 mg/l) as the limiting nutrient. Biofilms grown under laminar conditions were patchy and consisted of roughly circular cell clusters separated by interstitial voids. Biofilms in the turbulent flow cell were also patchy but these biofilms consisted of patches of ripples and elongated 'streamers' which oscillated in the flow. To assess the influence of changing nutrient conditions on biofilm structure the glucose concentration was increased from 40 to 400 mg/l on an established 21 day old biofilm growing in turbulent flow. The cell clusters grew rapidly and the thickness of the biofilm increased from 30 µm to 130 µm within 17 h. The ripples disappeared after 10 hours. After 5 d the glucose concentration was reduced back to 40 mg/l. There was a loss of biomass and patches of ripples were re-established within a further 2 d
The role of hydrodynamics and AHL signalling molecules as determinants of the structure of pseudomonas aeruginosa biofilms
No full textThe ability of two Pseudomonas aeruginosa PA01 wild type strains and two quorum sensing mutants to form biofilms in a recirculating continuous culture system was examined. Biofilms were grown under laminar and turbulent flow in parallel glass flow cells for between 9 and 12 d. One mutant, PANO67, is deficient in the production of BHL, however, it does produce OdDHL whereas a lasR lasI mutant does not produce OdDHL but is capable of producingBHL. The accumulation of biofilm biomass was estimated from the surface cover and the average microcolony thickness. The amount of biomass increased initially at a higher rate in the wild type strains than in the two quorum sensing mutants and a maximum was reached between 2 and 7 d after which there was some detachment of biofilm microcolonies. However, the biomass of the mutant strains steadily increased so that by the end of the experiments the mutant biofilms had a greater volume of biomass than the wild type strains. The results suggested no marked difference in the structure of the mutant biofilms compared to the wild type biofilms. However, the flow conditions had a profound influence on biofilm structure. Biofilms grown in turbulent flow consisted of filamentous streamers, while those grown in laminar flow consisted of a mono-layer of cells interspersed with circular microcolonies
Measuring fluid shear
No full textVery little is known about the material properties of dental biofilms. Unlike conventional materials like plastics, which can be molded into uniform test pieces, biofilms are nonuniform, microscopically small, and attached to surfaces. Removal from the surface will inevitably disrupt the sample, and it is difficult to reproduce in the lab the varying and complex physical forces existing in the mouth, so testing remains a challenge.In our laboratory at the Center for Biofilm Engineering at Montana State University, we have developed methods for testing the material properties of biofilms using fluid shear as the deforming force. By measuring the deformation to biofilms caused by long- and short-term exposure to elevated fluid shear, we found that various pure and mixed-species aerobic and anaerobic biofilms grown in glass flow cells were in fact viscous fluids that behaved elastically over short loading time periods (seconds or less), but could flow like viscous fluids when the load was sustained. Also, biofilms grown at higher shear were more firmly attached and cohesively stronger than those grown at lower shear.This has a number of implications. Because the mouth has an incredibly wide range of shear and normal stresses, we might expect that the biofilms will also exhibit a wide range of cohesive and adhesive strengths depending on the local growth environment in the mouth. The material properties of dental plaque will also likely change with time. As calcification occurs, the plaque will be expected to become more rigid and solid-like and behave less like a fluid. In this case, instead of flowing it may fracture in response to an applied physical force. Also, because biofilms can flow, albeit slowly, it is likely that the action of chewing or movement of the tongue may actually smear biofilm from one place to another. By looking at biofilms from a materials standpoint and refining our methods, we can begin to design new technologies to address their control
Rheology of biofilms
No full textThe paper describes an experimental study concerning the mechanical properties of bacterial biofilms formed from the early dental plaque colonizer Streptoccocus mutans and pond water biofilms. Experiments reported in this paper demonstrate that both types of biofilms exhibit mechanical behavior similar to that of rheological fluids. The time-dependent properties of both biofilms have been modeled using the principles of viscoelasticity theory. The Burger model has been found to accurately represent the response of both biofilms for the duration of the experiments. On this basis, the creep compliances of both biofilms have been characterized, and the respective relaxation functions have been determined analytically
Laser-Generated Shockwave for Clearing Medical Device Biofilms
No full textObjective: This study aimed to evaluate a laser method of biofilm interruption from the surface of various common medical devices and from surgically removed sinus tissue with adherent biofilms in a timely manner. Background: Biofilm has emerged as a new threat not amenable to most antibiotic treatments. Biofilms, as opposed to planktonic bacteria, develop an extracellular polymeric slime matrix to facilitate adherence to host tissue or a prosthetic surface and to form a protective shield. A laser-induced biofilms disruption concept was previously described. Materials and Methods: Biofilms were grown in the laboratory on metallic and plastic medical device surfaces such as stents. Attempts to remove the biofilms with a laser were undertaken three times for each device. Q-switched Nd:YAG laser-generated shockwaves affecting Pseudomonas aeruginosa biofilms expressing yellow fluorescent protein (YFP) biofilm coating were applied with biologically safe parameters utilizing a fiber delivery system and a special probe. A confocal microscope was used to identify the biofilm structure prior to, during, and after laser application. The amount of biofilm removed from the medical devices in time was measured by quantifying green fluorescence. Results: The biofilm fluctuated and eventually broke off the surface as shock waves neared the target. The time to remove 97.9±0.4% (mean±1SD, n=3) the biofilm from the surface of a Nitinol (NiTi) stent ranged from 4 to 10s. The detached biofilm was observed floating in fluid media in various microscopic size particles. Conclusions: A new treatment modality using laser-generated shockwaves in the warfare against biofilms growing on surgical devices was demonstrated. Q-switched laser pulses stripped biofilm from the surface it adhered to, changing the bacteria to their planktonic form, making them amenable to conventional treatment. This therapeutic modality appears to be rapid, effective, and safe on metallic and plastic medical device surfaces
Evidence for a biofilm based treatment strategy in the management of chronic hidradenitis suppurativa
No full textHidradenitis suppurativa (HS) is a chronic, inflammatory, debilitating skin disease of the hair follicle defined by recurrent, painful, deep‐seated and inflamed lesions.1 Although many aspects of the clinical presentation of HS is suggestive of infection, the role of the microbiology is still the subject of much debate. Polymicrobial‐positive cultures of skin bacteria are common but many cases are culture‐negative. Empirical antibiotic treatment returns mixed results in terms of resolving the disease. Interestingly, there are many similarities with otitis media with effusion (OME) in which there were conflicting data and opinions as to the role of bacteria in the chronic recurrent inflammation and whether the underlying cause was infection or a dysfunctional immune response.2 The bacterial biofilm paradigm of chronic disease may resolve some of these contradictions. Biofilms are aggregates of bacteria living within a protective extracellular polymeric slime matrix that adhere to indwelling devices and host tissue. When bacteria are in the biofilm phenotype they become highly tolerant of antibiotics and host immunity and elicit a chronic inflammatory response that causes damage to host tissue but fails to clear the infection. Chronic inflammation associated with bacterial biofilms is seen in diseases such as OME, the infected cystic fibrosis lung and periprosthetic joint infections (PJI).3 Because biofilm bacteria are notoriously difficult to culture and as there are no biofilm‐specific biomarkers, direct microscopic observation of biofilms is the best way to determine their presence with confocal laser scanning microscopy (CLSM) being the preferred method. Previously it was reported that bacterial biofilms were present in a case study of a patient with HS4 and this might provide a missing link between microbiology and chronic inflammation. In the present issue of the BJD, Ring et al.5 use peptide nucleic acid (PNA)–fluorescence in situ hybridization (FISH) (PNA)–FISH) and CLSM to demonstrate and map the presence of biofilms in chronic lesions of 42 patients with HS. Biofilms were seen in 67% of chronic lesions and 75% of the perilesional samples. The biofilms were heterogeneously distributed in discrete bacterial aggregates ranging from 5‐μm diameter up to more continuous patches > 50 μm, similar to those seen in OME and PJI specimens.2, 3 Importantly, the majority of the sinus tract samples (73%) contained active bacterial cells, which were associated with inflammation, thus suggesting the histology of HS may provide ideal settings for biofilm growth. This important study makes a clear link between a biofilm involvement and chronic inflammation in the late stages of the disease. However, other biofilm studies looking at clinically unaffected HS skin and samples from acute HS found little or no evidence of biofilms,6, 7 thus suggesting that biofilm formation is involved in exacerbating or possibly progressing the disease to later stages (Fig. 1). The mounting evidence that biofilms have an involvement in HS warrants consideration of a biofilm‐based treatment strategy such as is employed in other chronic wound biofilm infections8 in which a combination of high doses of locally administered antibiotics and aggressive early surgical excision or de‐roofing may reflect the most optimal treatment strategy for these patients
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