Ultrasound increases the rate of bacterial cell growth

Ultrasound as a treatment for chronic rhinosinusitis

Bacteria are now recognised as existing in two forms--free floating (planktonic) or in sophisticated communities called biofilms. Bacteria within biofilms are difficult to culture and highly refractory to antibiotic treatment. Biofilms could explain some of the paradoxes associated with chronic rhinosinusitis. Many patients are refractory to antibiotic therapy, bacteriology culture swabs frequently do not grow bacteria and positive bacteriology swabs often do not correlate with clinical findings. As antibiotics are largely ineffective in the treatment of bacterial biofilms, alternative therapeutic strategies including blocking molecular communication (quorum sensing) between bacteria, inhibiting biofilm matrix production and interventions that damage bacterial membranes are being explored as treatment options. So far these approaches have been largely unproductive. While physical therapies such as short wave diathermy and therapeutic ultrasound have been advocated as treatments for rhinosinusitis for many years, critical evaluation of these therapeutic interventions is virtually non-existent. Until recently any benefit has been difficult to explain using conventional microbiological paradigms. However, in the laboratory setting ultrasound enhances the killing of bacteria in biofilms both in vitro and in animal models. The successful application of ultrasound to sinus disease could mean the development of a new paradigm in our treatment of chronic rhinosinusits, a reduction in antibiotic resistance and improved medical management with a subsequent reduction in surgical intervention.

Bacteria-based controlled assembly of metal chalcogenide hollow nanostructures with enhanced light-harvesting and photocatalytic properties

Herein, a general bottom-up approach is proposed for the controlled assembly of metal chalcogenide nanoparticles into biomorphic porous hollow nanostructures by a sonochemical method using bacteria as morph-biotemplates. Biomorphic PbS and ZnS hollow nanostructures have been successfully synthesized with two species of bacteria cocci and bacillus as morph-templates. The biomorphic hollow assemblies possess shape-controllable, size-tunable and shell-thickness-adjustable characteristics. Thus, the structure and morphology of the hollow assemblies may be varied in a controllable way to tailor their properties over a broad range. A preliminary study on the light-harvesting properties of PbS and ZnS hollow spheres revealed that the hollow and porous structure is clearly far more favorable for the absorption of light than solid counterparts, which accounts for both multiple scattering effects at the large voids (hollow cavities) and Rayleigh scattering by nanovoids of the exterior shells. Furthermore, photocatalytic studies of ZnS nanostructures by degradation of acid fuchsine under solar irradiation have proved that the hollow structures possess superior photocatalytic activity to the corresponding solid counterparts. This versatile approach provides an effective route for the further extensive study of the distinct properties imparted by hollow nanostructures and extends their application potentials in photocatalysis and solar energy storage/conversion.

Improvement of the activity of anaerobic sludge by low-intensity ultrasound

This paper aims to study the enhancement effect of low-intensity ultrasound on anaerobic sludge activity and the efficiency of anaerobic wastewater treatment. Dehydrogenate activity (DHA) and the content of coenzyme F(420) were detected to indicate the change of activity of anaerobic sludge induced by ultrasound at 35 kHz. Single-factor and multiple-factor optimization experiments showed that the optimal ultrasonic intensity and irradiation period were 0.2 W/cm(2) and 10 min, respectively, and the biological activity was enhanced dramatically under the optimal condition. The chemical oxygen demand (COD) removal efficiency was increased by ultrasonic treatment and the COD in the effluent was 30% lower than that of the control (without exposure). The hypothetical mechanism of biological activity enhancement by ultrasound was also discussed according to the results.

Using low intensity ultrasound to improve the efficiency of biological phosphorus removal

Low intensity ultrasound can produce various effects on biological materials, such as stimulating enzyme activity, cell growth, biosynthesis, etc., which may improve the efficiency of enhanced biological phosphorus removal (EBPR). We adopt total phosphorus (TP) and dehydrogenase activity (DHA) as indicators to confirm the feasibility of applying low intensity ultrasound in EBPR. Single-factor experiments and orthogonal test were conducted in batch anaerobic/oxic (A/O) process simulation to study the influence of ultrasonic intensity and exposure time in the EBPR process. The results showed that the optimal ultrasonic parameters were 0.2 W/cm2 and 10 min under which condition the TP concentration in the effluent was 35-50% lower than that of the control (without ultrasonic irradiation). Changes of sludge activities after ultrasonic irradiation were examined. The improvement of sludge activity by ultrasound took 4 h after irradiation to reach the peak level, when an increase above 50% of DHA has been achieved by ultrasonic irradiation, and the enhancing effects induced by ultrasound disappeared in 16 h after irradiation. A tentative mechanism of biological phosphorus removal enhancement stimulated by ultrasound was discussed based on these phenomena.

Sonication of removed hip and knee prostheses for diagnosis of infection

BACKGROUND

Culturing of samples of periprosthetic tissue is the standard method used for the microbiologic diagnosis of prosthetic-joint infection, but this method is neither sensitive nor specific. In prosthetic-joint infection, microorganisms are typically present in a biofilm on the surface of the prosthesis. We hypothesized that culturing of samples obtained from the prosthesis would improve the microbiologic diagnosis of prosthetic-joint infection.

METHODS

We performed a prospective trial comparing culture of samples obtained by sonication of explanted hip and knee prostheses to dislodge adherent bacteria from the prosthesis with conventional culture of periprosthetic tissue for the microbiologic diagnosis of prosthetic-joint infection among patients undergoing hip or knee revision or resection arthroplasty.

RESULTS

We studied 331 patients with total knee prostheses (207 patients) or hip prostheses (124 patients); 252 patients had aseptic failure, and 79 had prosthetic-joint infection. With the use of standardized nonmicrobiologic criteria to define prosthetic-joint infection, the sensitivities of periprosthetic-tissue and sonicate-fluid cultures were 60.8% and 78.5% (P<0.001), respectively, and the specificities were 99.2% and 98.8%, respectively. Fourteen cases of prosthetic-joint infection were detected by sonicate-fluid culture but not by prosthetic-tissue culture. In patients receiving antimicrobial therapy within 14 days before surgery, the sensitivities of periprosthetic tissue and sonicate-fluid culture were 45.0% and 75.0% (P<0.001), respectively.

CONCLUSIONS

In this study, culture of samples obtained by sonication of prostheses was more sensitive than conventional periprosthetic-tissue culture for the microbiologic diagnosis of prosthetic hip and knee infection, especially in patients who had received antimicrobial therapy within 14 days before surgery.

Towards a Detailed Understanding of Bacterial Metabolism—Spectroscopic Characterization ofStaphylococcus Epidermidis

Bacteria are a major cause of infection. To fight disease and growing resistance, research interest is focused on understanding bacterial metabolism. For a detailed evaluation of the involved mechanisms, a precise knowledge of the molecular composition of the bacteria is required. In this article, various vibrational spectroscopic techniques are applied to comprehensively characterize, on a molecular level, bacteria of the strain Staphylococcus epidermidis, an opportunistic pathogen which has evolved to become a major cause of nosocomial infections. IR absorption spectroscopy reflects the overall chemical composition of the cells, with major focus on the protein vibrations. Smaller sample volumes-down to a single cell-are sufficient to probe the overall chemical composition by means of micro-Raman spectroscopy. The nucleic-acid and aromatic amino-acid moieties are almost exclusively explored by UV resonance Raman spectroscopy. In combination with statistical evaluation methods [hierarchical cluster analysis (HCA), principal component analysis (PCA), linear discriminant analysis (LDA)], the protein and nucleic-acid components that change during the different bacterial growth phases can be identified from the in vivo vibrational spectra. Furthermore, tip-enhanced Raman spectroscopy (TERS) provides insight into the surface structures and follows the dynamics of the polysaccharide and peptide components on the bacterial cells with a spatial resolution below the diffraction limit. This might open new ways for the elucidation of host-bacteria and drug-bacteria interactions.

Biofilms and antimicrobial resistance

The pathogenesis of many orthopaedic infections is related to the presence of microorganisms in biofilms. I examine the emerging understanding of the mechanisms of biofilm-associated antimicrobial resistance. Biofilm-associated resistance to antimicrobial agents begins at the attachment phase and increases as the biofilm ages. A variety of reasons for the increased antimicrobial resistance of microorganisms in biofilms have been postulated and investigated. Although bacteria in biofilms are surrounded by an extracellular matrix that might physically restrict the diffusion of antimicrobial agents, this does not seem to be a predominant mechanism of biofilm-associated antimicrobial resistance. Nutrient and oxygen depletion within the biofilm cause some bacteria to enter a nongrowing (ie, stationary) state, in which they are less susceptible to growth-dependent antimicrobial killing. A subpopulation of bacteria might differentiate into a phenotypically resistant state. Finally, some organisms in biofilms have been shown to express biofilm-specific antimicrobial resistance genes that are not required for biofilm formation. Overall, the mechanism of biofilm-associated antimicrobial resistance seems to be multifactorial and may vary from organism to organism. Techniques that address biofilm susceptibility testing to antimicrobial agents may be necessary before antimicrobial regimens for orthopaedic prosthetic device-associated infections can be appropriately defined in research and clinical settings. Finally, a variety of approaches are being defined to overcome biofilm-associated antimicrobial resistance.

Infections associated with medical devices: pathogenesis, management and prophylaxis

The insertion or implantation of foreign bodies has become an indispensable part in almost all fields of medicine. However, medical devices are associated with a definitive risk of bacterial and fungal infections. Foreign body-related infections (FBRIs), particularly catheter-related infections, significantly contribute to the increasing problem of nosocomial infections. While a variety of micro-organisms may be involved as pathogens, staphylococci account for the majority of FBRIs. Their ability to adhere to materials and to promote formation of a biofilm is the most important feature of their pathogenicity. This biofilm on the surface of colonised foreign bodies is regarded as the biological correlative for the clinical experience with FBRI, that is, that the host defence mechanisms often seem to be unable to handle the infection and, in particular, to eliminate the micro-organisms from the infected device. Since antibacterial chemotherapy is also frequently not able to cure these infections despite the use of antibacterials with proven in vitro activity, removal of implanted devices is often inevitable and has been standard clinical practice. However, in specific circumstances, such as infections of implanted medical devices with coagulase-negative staphylococci, a trial of salvage of the device may be justified. All FBRIs should be treated with antibacterials to which the pathogens have been shown to be susceptible. In addition to systemic antibacterial therapy, an intraluminal application of antibacterial agents, referred to as the 'antibiotic-lock' technique, should be considered to circumvent the need for removal, especially in patients with implanted long-term catheters. To reduce the incidence of intravascular catheter-related bloodstream infections, specific guidelines comprising both technological and nontechnological strategies for prevention have been established. Quality assurance, continuing education, choice of the catheter insertion site, hand hygiene and aseptic techniques are aspects of particular interest. Furthermore, all steps in the pathogenesis of biofilm formation may represent targets against which prevention strategies may be directed. Alteration of the foreign body material surface may lead to a change in specific and nonspecific interactions with micro-organisms and, thus, to a reduced microbial adherence. Medical devices made out of a material that would be antiadhesive or at least colonisation resistant would be the most suitable candidates to avoid colonisation and subsequent infection. Another concept for the prevention of FBRIs involves the impregnation of devices with various substances such as antibacterials, antiseptics and/or metals. Finally, further studies are needed to translate the knowledge on the mechanisms of biofilm formation into applicable therapeutic and preventive strategies.

Bioleaching with ultrasound

Application of bioleaching of metals in a large-scale operation is reviewed briefly. Continued technical innovation is vital for the wider utilisation of this extraction process within the mineral industries. Therefore, the use of power ultrasound in combination with bioleaching (referred to as sonobioleaching) has been studied and is shown to be beneficial in the recovery of nickel from lean grade ores. The role of ultrasound in improving the benefits and lowering the drawbacks of bioleaching to an acceptable level are described. A possible mechanism for improving and intensifying this process is hypothesised.

Ultrasonic drug delivery--a general review

Ultrasound has an ever-increasing role in the delivery of therapeutic agents, including genetic material, protein and chemotherapeutic agents. Cavitating gas bodies, such as microbubbles, are the mediators through which the energy of relatively non-interactive pressure waves is concentrated to produce forces that permeabilise cell membranes and disrupt the vesicles that carry drugs. Thus, the presence of microbubbles enormously enhances ultrasonic delivery of genetic material, proteins and smaller chemical agents. Numerous reports show that the most efficient delivery of genetic material occurs in the presence of cavitating microbubbles. Attaching the DNA directly to the microbubbles, or to gas-containing liposomes, enhances gene uptake even further. Ultrasonic-enhanced gene delivery has been studied in various tissues, including cardiac, vascular, skeletal muscle, tumour and even fetal tissue. Ultrasonic-assisted delivery of proteins has found most application in transdermal transport of insulin. Cavitation events reversibly disrupt the structure of the stratus corneum to allow transport of these large molecules. Other hormones and small proteins could also be delivered transdermally. Small chemotherapeutic molecules are delivered in research settings from micelles and liposomes exposed to ultrasound. Cavitation appears to play two roles: it disrupts the structure of the carrier vesicle and releases the drug; and makes cell membranes and capillaries more permeable to drugs. There remains a need to better understand the physics of cavitation of microbubbles and the impact that such cavitation has on cells and drug-carrying vesicles.

Ultrasonic-enhanced gentamicin transport through colony biofilms of Pseudomonas aeruginosa and Escherichia coli

The hypothesis that ultrasound increases antibiotic transport through biofilms of Escherichia coli and Pseudomonas aeruginosa was investigated using colony biofilms. Biofilms grown on membrane filters were transferred to nutrient agar containing 50 microg/ml gentamicin. A smaller filter was placed on top of the biofilm and a blank concentration disk was situated atop the filter. Diffusion of antibiotic through the biofilms was allowed for 15, 30, or 45 min at 37 degrees C. Some of these biofilms were exposed to 70-kHz ultrasound and others were not. Each concentration disk was then placed on a nutrient agar plate spread with a lawn of E. coli. The resulting zone of inhibition was used to calculate the amount of gentamicin that was transported through the biofilm into the disk. The E. coli and P. aeruginosa biofilms grown for 13 and 24 h were exposed to two different ultrasonic power densities. Ultrasonication significantly increased the transport of gentamicin through the biofilm. Insonation of biofilms of E. coli for 45 min more than doubled the amount of gentamicin compared to their noninsonated counterparts. For P. aeruginosa biofilms, no detectable gentamicin penetrated the biofilm within 45 min without ultrasound; however, when insonated (1.5 W/cm2) for 45 min, the disks collected more than 0.45 microg antibiotic. Ultrasonication significantly increased transport of gentamicin across biofilms that normally blocked or slowed gentamicin transport when not exposed to ultrasound. This enhanced transport may be partially responsible for the increased killing of biofilm bacteria exposed to combinations of antibiotic and ultrasound.

Ultrasonically enhanced vancomycin activity against Staphylococcus epidermidis biofilms in vivo

Infection of implanted medical devices by Gram-positive organisms such as Staphylococcus ssp. is a serious concern in the biomaterial community. In this research the application of low frequency ultrasound to enhance the activity of vancomycin against implanted Staphylococcus epidermidis biofilms was examined. Polyethylene disks covered with a biofilm of S. epidermidis were implanted subcutaneously in rabbits on both sides of their spine. The rabbits received systemic vancomycin for the duration of the experiment. Following 24 h of recovery, one disk was insonated for 24 or 48 h while the other was a control. Disks were removed and viable bacteria counted. At 24 h of insonation, there was no difference in viable counts between control and insonated biofilms, while at 48 h of insonation there were statistically fewer viable bacteria in the insonated biofilm. The S. epidermidis biofilms responded favorably to combinations of ultrasound and vancomycin, but longer treatment times are required for this Gram-positive organism than was observed previously for a Gram-negative species.