Safety assessment of Streptococcus salivarius M18 a probiotic for oral health.

The development of probiotics targeting non-intestinal body sites continues to generate interest amongst researchers, biotech companies and consumers alike. A key consideration for any bacterial strain to be developed into a probiotic is a robust assessment of its safety profile. Streptococcus salivarius strain M18 was originally isolated from a healthy adult and evaluated for its probiotic capabilities targeted to dental and oral health applications. This publication presents the safety characterisation of strain M18. Application of a diverse range of techniques showed that strain M18 can be specifically distinguished from other S. salivarius using a variety of molecular and phenotypic methodologies and that it lacks any relevant antibiotic resistance or virulence determinants. Direct comparison of the strain M18 safety profile with that of the prototype S. salivarius probiotic, S. salivarius strain K12, supports the proposition that strain M18 is indeed safe for probiotic application in humans.

Deciphering the mode of action of the synthetic antimicrobial peptide Bac8c.

Bac8c (RIWVIWRR-NH(2)) is an 8-amino-acid peptide derived from Bac2A (RLARIVVIRVAR-NH(2)), a C3A/C11A variant of the naturally occurring bovine peptide, bactenecin (also known as bovine dodecapeptide), the smallest peptide with activity against a range of pathogenic Gram-positive and Gram-negative bacteria, as well as yeast. The effects of Bac8c on Escherichia coli were examined by studying its bacteriostatic and bactericidal properties, demonstrating its effects on proton motive force generation, and visually analyzing (via transmission electron microscopy) its effects on cells at different concentrations, in order to probe the complexities of the mechanism of action of Bac8c. Results were consistent with a two-stage model for the Bac8c mode of action. At sublethal concentrations (3 µg/ml), Bac8c addition resulted in transient membrane destabilization and metabolic imbalances, which appeared to be linked to inhibition of respiratory function. Although sublethal concentrations resulted in deleterious downstream events, such as methylglyoxal formation and free radical generation, native E. coli defense systems were sufficient for full recovery within 2 h. In contrast, at the minimal bactericidal concentration (6 µg/ml), Bac8c substantially but incompletely depolarized the cytoplasmic membrane within 5 min and disrupted electron transport, which in turn resulted in partial membrane permeabilization and cell death.

Genetic basis for mutacin N and of its relationship to mutacin I.

BACKGROUND & OBJECTIVES: The mutans streptococci (MS) are a group of 7 species of dental cariesassociated bacteria of which Streptococcus mutans and Streptococcus sobrinus are the most important in humans. Many MS produce bacteriocin-like inhibitory substances (BLIS), some of which have been characterised as small peptides capable of inhibiting the growth of closely-related species. These peptides have most commonly been referred to as mutacins. S. mutans strains N and UA140 appear to have closely similar BLIS activities. Both produce mutacins that seem to target the same species of bacteria. On closer analysis however, these two strains have been shown to produce distinctly different mutacins, known as mutacin N and mutacin I respectively. In the present study the mutacin N structural gene (mutN) was cloned and compared with the mutacin I structural gene (mutA). METHODS: Cloning and sequencing of S. mutans N was done. The distribution of mutN using DNA from 216 streptococcal strains was determined by dot blotting. RESULTS: Mut N was cloned and sequenced from an 1800 bp Bam HI/Eco RI fragment. PCR with the mutN primers mutNF and mutNR on the four mutN-positive strains identified identical bands to S. mutans N. The location of mutN differs significantly from that of mutA in that it is directly upstream of comC, a gene encoding a putative competence stimulating factor. INTERPRETATION & CONCLUSION: The close upstream proximity of mutN to comC suggests a link between mutacin N production and competence development. Further studies need to be done to detect competence-related genes in S. mutans strain N.

Evaluation of truncated readout-echo MR images obtained at 0.35 T.

It is possible to acquire a truncated echo, in which part of the information at the beginning or end of the echo is missing, and to restore the missing information by conjugation. This process was shown by means of edge spread function in phantoms and brain images in volunteers to introduce little, if any, degradation of image quality and can be used to improve sequence efficiency or to shorten echo time.

Impact of section doubling on MR angiography.

To improve the quality of projection angiograms generated from three-dimensional magnetic resonance (MR) angiography data, the authors applied voxel shifting to create intermediate sections ("section doubling") prior to maximum intensity projection. To date, the authors have processed MR angiography studies with and without section doubling in 20 cases. Section doubling resulted in improved vessel contrast and delineation of continuity (especially of small vessels) in all cases.

Impact of section doubling on lesion contrast.

Misregistration between section position and a feature of interest, such as a lesion, can result in loss of contrast on magnetic resonance images. Because the section direction typically has the poorest resolution, reduction of section misregistration can improve lesion contrast. Lesions occur at random sites; hence, to reduce misregistration, it is necessary to repeat imaging with a small amount of offset. This is impractical. Therefore, a reconstruction algorithm that yields offset sections was implemented, in which sections were produced with a zero- and a half-section shift. This algorithm was tested in 14 patients with multiple sclerosis. As expected, because of randomness associated with section placement relative to lesions, the half-shifted sections provided greater contrast as often as the zero-shifted sections. The combined set improved contrast significantly in 39% of lesions; improvement was greatest in lesions with lesser contrast. Signal-to-noise ratios were not affected by this process, which appears to be useful in magnetic resonance image reconstruction.

Identification of aortic thrombus by magnetic resonance imaging.

The unique properties of magnetic resonance imaging result in the potential to differentiate various components of the diseased arterial wall. In this article four cases are presented in which magnetic resonance imaging showed mural aortic thrombus and its anatomic relationship to the visceral and renal arteries. Once thrombus is identified and localized specific operative strategies can be undertaken to prevent recurrent embolic events and/or avoid perioperative thromboembolic complications.

Echo-planar pediatric imager.

Practical constraints make it difficult to build large-aperture echo-planar magnetic resonance (MR) imagers. The implementation of a pediatric imager and its performance are described. Spatial resolution and signal-to-noise levels comparable to those of 1982 state-of-the-art MR imagers have been achieved in imaging times of 0.05-0.15 seconds. T1 and T2 information are obtainable in the echo-planar mode. A major issue is that of chemical-shift displacements.

Halving MR imaging time by conjugation: demonstration at 3.5 kG.

Conjugation can be used to synthesize half of the data acquired during a conventional two-dimensional Fourier transform imaging procedure, thus reducing imaging time by nearly half. The images acquired by this process have the same object contrast and spatial resolution as conventional images do, but with a 40% reduction in the signal-to-noise ratio (S/N). Conjugation can be used to advantage in magnetic resonance imaging units in which S/N levels are higher than needed to permit imaging with a single acquisition of each projection.

MRI of blood flow: correlation of image appearance with spin-echo phase shift and signal intensity.

Phase-sensitive imaging was used to correlate signal distribution with phase shift and velocity distribution in spin-echo magnetic resonance imaging (MRI). Flow-dependent, changing intensity patterns that were seen in a constant-flow phantom study were explained by the simultaneous effects of inflow signal enhancement, first-echo dephasing, and outflow signal loss occurring during laminar flow. In clinical studies, first-echo dephasing was shown during laminar flow in the inferior vena cava. Turbulent flow was demonstrated in the descending thoracic aorta during late systolic flow, and turbulent dephasing-rephasing was shown in the abdominal aorta.

MR imaging of aortoiliac atherosclerosis with 3D image reconstruction.

A computer program was written to detect blood flow in a sequence of magnetic resonance images, using reduction in first echo intensity and prolongation of calculated T2 value, and to construct three-dimensional vessel maps from the detected flow regions. Reconstructed vessel images were coded to show cross-sectional area of the lumen and relative flow velocity along the length of the vessel. The program was applied to imaging the aorta and iliac arteries in 11 patients with atherosclerosis and results were compared with angiography. All sites of narrowing were identified by the algorithm, but no flow at all was detected at one site of partial occlusion.

Magnetic resonance applications in atherosclerotic vascular disease.

Magnetic resonance imaging of the cardiovascular system offers great promise in the detection and characterization of the anatomic, physiologic, and biochemical consequences of atherosclerosis. This review will focus on the potential applications of MRI for evaluating atherosclerosis of the abdominal aorta and iliofemoral vessels.

MR imaging of the aorta with three-dimensional vessel reconstruction: validation by angiography.

Longitudinal vascular structures are difficult to observe on the standard abdominal transaxial magnetic resonance (MR) image sections. To display the information in a three-dimensional reconstruction, an algorithm was written to identify blood flow in a series of transaxial MR sections and was applied to reconstructing images of the aorta and iliac arteries in 12 patients with aortic aneurysm, dissection, or aortoiliac atherosclerosis. Results were validated by angiography. In all patients, the outline of the flow channel in the reconstructed image followed closely the outline of the lumen on angiograms. In aortic dissection, the MR images showed the two lumens more completely than did the angiograms, and in atherosclerosis, sites of vascular stenosis were correctly identified on MR images. The technique is valuable in providing anatomic information as well as functional information on cross-sectional areas and relative flow velocities.

MR imaging of blood vessels using three-dimensional reconstruction: methodology.

Multisection, dual-echo magnetic resonance (MR) transaxial images of blood vessels contain both anatomic and qualitative information about flow. Even so, the images are produced as a series of two-dimensional tomographic sections from which full visualization of connected structures is difficult. A computer algorithm was developed that automatically detects flowing blood based on pixel intensity and calculated T2 and provides reconstructed views of vessels while analyzing and displaying flow characteristics. Images of abdominal vessels, aortic aneurysms, and the heart were encoded by flow and color to demonstrate depth. In addition, these data were reconstructed to derive a more accurate assessment of patency. With this technique, transaxial images can be used to analyze flow patterns, determine patent areas, and visualize all levels of vessels in a single image.

Peripheral vascular disease: correlation of MR imaging and angiography.

The capability of magnetic resonance (MR) imaging for detecting aortic, iliac, and femoral stenoses and occlusions was evaluated. Multisection spin-echo studies at 0.35 tesla were obtained of the infrarenal aorta to the femoral bifurcation in 24 patients, all of whom had undergone intraarterial angiography within 14 days of imaging. Transaxial MR images were compared with the angiograms. Arterial stenoses and occlusions in these vessels detected by MR imaging correlated with angiographic findings in 91% of the instances. Protrusional atherosclerotic plaques and occlusions and stenoses in the aortoiliac region were demonstrated accurately on MR images; complications of previous vascular surgery, such as aneurysms at sites of previous anastomoses or endarterectomy, were also identified. Due to the limited spatial resolution, MR images failed to demonstrate some femoral stenoses. MR imaging may be used for evaluation of aortoiliac vascular disease and for follow-up study after surgical revascularization. However, the limited spatial resolution, noncomposite display of the aortoiliofemoral circulation, and lack of evaluation of peripheral runoff provided by current MR imaging techniques militate against its replacing angiography prior to vascular intervention.