PubMed · 8518078
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P Y Lee, M J Martin, T Treasure. 1993. Propionibacterium acnes causing perivalve abscess.. https://doi.org/10.1136/hrt.69.5.470-b
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The staphylococcal virulon is controlled largely by the agr locus, a global accessory gene regulator that is autoinduced by a self-coded peptide (AIP) and is therefore a quorum sensor. The agr locus has diverged within and between species, giving rise to AIP variants that inhibit heterologous agr activation, an effect with therapeutic potential against Staphylococcus aureus: a single dose of an inhibitory AIP blocks the formation of an experimental murine abscess. As the AIP is unstable at physiological pH, owing to its essential thiolactone bond, its single-dose efficacy seems paradoxical, which has led us to analyze the in vivo kinetics of agr activation and the consequences of its blockage by a heterologous AIP. Initially, the infecting bacteria grow rapidly, achieving sufficient population density within the first 3 h to activate agr, and then enter a neutrophil-induced metabolic eclipse lasting for 2-3 d, followed by agr reactivation concomitantly with the development of the abscess. The inhibitory AIP prevents agr expression only during its short in vivo lifetime, suggesting that the agr-induced and therefore quorum-dependent synthesis of virulence factors shortly after infection is necessary for the subsequent development of the abscess lesion and bacterial survival. We confirm this finding by showing that a sterile agr+ supernatant causes a sterile abscess similar to the septic abscess caused by live bacteria. These results may provide a biological rationale for regulation of virulence factor expression by quorum sensing rather than by response to specific host signals.
PURPOSE: To describe dose-dependent signal intensity (SI) characteristics of experimentally induced soft-tissue abscesses on 1.5-T T1- and T2*-weighted magnetic resonance (MR) images obtained 24 hours after administration of ultrasmall superparamagnetic iron oxide (USPIO) and to describe the relationship between SI and amount of USPIO uptake and macrophage iron content. MATERIALS AND METHODS: Local institutional review committee on animal care approved the experiments, which were performed according to the guidelines of the National Institutes of Health and the committee on animal research at our institution. Unilateral calf muscle abscesses were induced in 21 rats with an injection of a Staphylococcus aureus suspension. The rats were divided into three groups of seven animals each: low USPIO dose (50 micromol of iron per kilogram of body weight), high USPIO dose (150 micromol Fe/kg), and control (saline solution). All rats were imaged before and 24 hours after USPIO administration at 1.5 T (transverse T1-weighted spin-echo, T2*-weighted fast gradient-echo, and short inversion time inversion-recovery sequences). Images were analyzed quantitatively and qualitatively with regard to SI and signal pattern. Temporal variation of calculated contrast-to-noise ratios was analyzed with the Wilcoxon signed rank test. MR findings were correlated with histopathologic findings, including those of electron microscopy. RESULTS: Twenty-four hours after USPIO administration in the high-dose group, susceptibility effects were present in abscess periphery on postcontrast T2*-weighted images (P=.04), and SI enhancement was noted on postcontrast T1-weighted images within both abscess wall and abscess center (P=.04 for both). In the low-dose group, SI enhancement was noted in entire abscess on T1-weighted postcontrast images (P=.03). Neither significant SI loss (P=.09) nor susceptibility effects were detected in periphery or center of any abscess on postcontrast T2*-weighted images. There was no obvious difference in total amount of macrophages among the groups, but there was a clear difference with regard to individual iron content of iron-positive macrophages between the USPIO dose groups. CONCLUSION: At 1.5 T, SI characteristics of abscesses on T1- and T2*-weighted images obtained 24 hours after USPIO injection strongly depend on administered dose of the contrast agent. At low doses, T1 effects were stronger than T2* effects.
PURPOSE: To evaluate a transgluteal approach for draining pelvic fluid collections in pediatric patients. MATERIALS AND METHODS: Institutional review board approval and informed consent for interventional procedures were obtained. From September 1995 to December 2002, 140 abdominopelvic fluid collections were drained at two institutions. Retrospective analysis of a prospectively gathered procedural database revealed that a transgluteal approach was used to drain 53 of these 140 collections (38%) in 51 patients (29 female, 22 male; mean age, 11.2 years; age range, 0.2-19 years). All patients received antibiotics before the procedure. A retrospective analysis was conducted of the patients' medical records and diagnostic imaging and interventional procedure findings, including the reason for referral; location, volume, and character of collections; method and equipment used for evacuation; duration of therapy; evidence of complications; results of microbiologic examination of specimens; and success rates. RESULTS: Transgluteal drainage was performed with computed tomographic (CT) guidance in 45 of the 53 collections (85%), with fluoroscopic guidance in three (6%), and with a combination of both modalities in five (9%). A drainage catheter was successfully placed in 49 collections; four small collections were aspirated without drain placement. Infected fluid was obtained from 41 collections, and serosanguineous fluid was obtained from 12 collections. The mean volume aspirated was 80 mL (2-600 mL). A positive culture was obtained at 28 of the 53 procedures. The mean duration of catheter placement was 4 days (range, 2-14 days). There were no major complications. CONCLUSION: The transgluteal approach to the drainage of abdominopelvic fluid collections with imaging guidance is safe and effective.