Lipopolysaccharide structure modulates cationic biocide susceptibility and crystalline biofilm formation in Proteus mirabilis.

Chlorhexidine (CHD) is a cationic biocide used ubiquitously in healthcare settings. Proteus mirabilis, an important pathogen of the catheterized urinary tract, and isolates of this species are often described as "resistant" to CHD-containing products used for catheter infection control. To identify the mechanisms underlying reduced CHD susceptibility in P. mirabilis, we subjected the CHD tolerant clinical isolate RS47 to random transposon mutagenesis and screened for mutants with reduced CHD minimum inhibitory concentrations (MICs). One mutant recovered from these screens (designated RS47-2) exhibited ~ 8-fold reduction in CHD MIC. Complete genome sequencing of RS47-2 showed a single mini-Tn5 insert in the waaC gene involved in lipopolysaccharide (LPS) inner core biosynthesis. Phenotypic screening of RS47-2 revealed a significant increase in cell surface hydrophobicity and serum susceptibility compared to the wildtype, and confirmed defects in LPS production congruent with waaC inactivation. Disruption of waaC was also associated with increased susceptibility to a range of other cationic biocides but did not affect susceptibility to antibiotics tested. Complementation studies showed that repression of smvA efflux activity in RS47-2 further increased susceptibility to CHD and other cationic biocides, reducing CHD MICs to values comparable with the most CHD susceptible isolates characterized. The formation of crystalline biofilms and blockage of urethral catheters was also significantly attenuated in RS47-2. Taken together, these data show that aspects of LPS structure and upregulation of the smvA efflux system function in synergy to modulate susceptibility to CHD and other cationic biocides, and that LPS structure is also an important factor in P. mirabilis crystalline biofilm formation.

ADC Histogram Analysis of Pediatric Low-Grade Glioma Treated with Selumetinib: A Report from the Pediatric Brain Tumor Consortium.

BACKGROUND AND PURPOSE: Selumetinib is a promising MAP (mitogen-activated protein) kinase (MEK) 1/2 inhibitor treatment for pediatric low-grade gliomas. We hypothesized that MR imaging-derived ADC histogram metrics would be associated with survival and response to treatment with selumetinib. MATERIALS AND METHODS: Children with recurrent, refractory, or progressive pediatric low-grade gliomas who had World Health Organization grade I pilocytic astrocytoma with KIAA1549-BRAF fusion or the BRAF V600E mutation (stratum 1), neurofibromatosis type 1-associated pediatric low-grade gliomas (stratum 3), or sporadic non-neurofibromatosis type 1 optic pathway and hypothalamic glioma (OPHG) (stratum 4) were treated with selumetinib for up to 2 years. Quantitative ADC histogram metrics were analyzed for total and enhancing tumor volumes at baseline and during treatment. RESULTS: Each stratum comprised 25 patients. Stratum 1 responders showed lower values of SD of baseline ADC_total as well as a larger decrease with time on treatment in ADC_total mean, mode, and median compared with nonresponders. Stratum 3 responders showed a greater longitudinal decrease in ADC_total. In stratum 4, higher baseline ADC_total skewness and kurtosis were associated with shorter progression-free survival. When all 3 strata were combined, responders showed a greater decrease with time in ADC_total mode and median. Compared with sporadic OPHG, neurofibromatosis type 1-associated OPHG had lower values of ADC_total mean, mode, and median as well as ADC_enhancement mean and median and higher values of ADC_total skewness and kurtosis at baseline. The longitudinal decrease in ADC_total median during treatment was significantly greater in sporadic OPHG compared with neurofibromatosis type 1-associated OPHG. CONCLUSIONS: ADC histogram metrics are associated with progression-free survival and response to treatment with selumetinib in pediatric low-grade gliomas.

De-repression of the smvA efflux system arises in clinical isolates of Proteus mirabilis and reduces susceptibility to chlorhexidine and other biocides.

Proteus mirabilis is a common pathogen of the catheterised urinary tract and often described as intrinsically resistant to the biocide chlorhexidine (CHD). Here we demonstrate that de-repression of the smvA efflux system has occurred in clinical isolates of P. mirabilis and reduces susceptibility to CHD and other cationic biocides. Compared to other isolates examined, P. mirabilis RS47 exhibited a significantly higher CHD MIC (≥512 µg/ml) and significantly greater expression of smvA. Comparison of the RS47 smvA and cognate smvR repressor with sequences from other isolates, indicated that RS47 encodes an inactivated smvR. Complementation of RS47 with a functional smvR from isolate RS50a (which exhibited the lowest smvA expression and lowest CHD MIC) reduced smvA expression by ∼59-fold, and markedly lowered the MIC of CHD and other cationic biocides. Although complementation of RS47 did not reduce MICs to concentrations observed in isolate RS50a, the significantly lower polymyxin B MIC of RS50a indicated that differences in LPS structure are also a factor in P. mirabilis CHD susceptibility. To determine if exposure to CHD can select for mutations in smvR, clinical isolates with the lowest CHD MICs were adapted to grow at increasing concentrations of CHD up to 512 µg/ml. Analysis of the smvR in adapted populations indicated that mutations predicted to inactivate smvR occurred following CHD exposure in some isolates. Collectively, our data show that smvA de-repression contributes to reduced biocide susceptibility in P. mirabilis, but differences in LPS structure between strains are also likely to be an important factor.

Bacterial biofilm formation on indwelling urethral catheters.

Urethral catheters are the most commonly deployed medical devices and used to manage a wide range of conditions in both hospital and community care settings. The use of long-term catheterization, where the catheter remains in place for a period >28 days remains common, and the care of these patients is often undermined by the acquisition of infections and formation of biofilms on catheter surfaces. Particular problems arise from colonization with urease-producing species such as Proteus mirabilis, which form unusual crystalline biofilms that encrust catheter surfaces and block urine flow. Encrustation and blockage often lead to a range of serious clinical complications and emergency hospital referrals in long-term catheterized patients. Here we review current understanding of bacterial biofilm formation on urethral catheters, with a focus on crystalline biofilm formation by P. mirabilis, as well as approaches that may be used to control biofilm formation on these devices. SIGNIFICANCE AND IMPACT OF THE STUDY: Urinary catheters are the most commonly used medical devices in many healthcare systems, but their use predisposes to infection and provide ideal conditions for bacterial biofilm formation. Patients managed by long-term urethral catheterization are particularly vulnerable to biofilm-related infections, with crystalline biofilm formation by urease producing species frequently leading to catheter blockage and other serious clinical complications. This review considers current knowledge regarding biofilm formation on urethral catheters, and possible strategies for their control.

Prototype Development of the Intelligent Hydrogel Wound Dressing and Its Efficacy in the Detection of Model Pathogenic Wound Biofilms.

The early detection of wound infection in situ can dramatically improve patient care pathways and clinical outcomes. There is increasing evidence that within an infected wound the main bacterial mode of living is a biofilm: a confluent community of adherent bacteria encased in an extracellular polymeric matrix. Here we have reported the development of a prototype wound dressing, which switches on a fluorescent color when in contact with pathogenic wound biofilms. The dressing is made of a hydrated agarose film in which the fluorescent dye containing vesicles were mixed with agarose and dispersed within the hydrogel matrix. The static and dynamic models of wound biofilms, from clinical strains of Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Enterococcus faecalis, were established on nanoporous polycarbonate membrane for 24, 48, and 72 h, and the dressing response to the biofilms on the prototype dressing evaluated. The dressing indicated a clear fluorescent/color response within 4 h, only observed when in contact with biofilms produced by a pathogenic strain. The sensitivity of the dressing to biofilms was dependent on the species and strain types of the bacterial pathogens involved, but a relatively higher response was observed in strains considered good biofilm formers. There was a clear difference in the levels of dressing response, when dressings were tested on bacteria grown in biofilm or in planktonic cultures, suggesting that the level of expression of virulence factors is different depending of the growth mode. Colorimetric detection on wound biofilms of prevalent pathogens (S. aureus, P. aeruginosa, and E. faecalis) is also demonstrated using an ex vivo porcine skin model of burn wound infection.

Increased Prevalence of Developmental Venous Anomalies in Children with Intracranial Neoplasms.

BACKGROUND AND PURPOSE: Developmental venous anomalies are considered variants of venous development that, in and of themselves, are of little clinical import. A possible association between intrinsic brain tumors and developmental venous anomalies has been suggested, but a rigorous investigation has not been performed. The aim of this study was to assess any association between developmental venous anomalies and intrinsic brain neoplasms. MATERIALS AND METHODS: A radiology report text search of terms used to describe developmental venous anomalies was performed on a study population of 580 patients with primary intracranial neoplasms and on a control population of 580 patients without neoplasms from the same time period. All positive results were reviewed to confirm that the report was describing a developmental venous anomaly, and the imaging examination was reviewed to confirm the diagnosis. RESULTS: Fifty-nine of the 580 subjects with brain tumors (10.17%) had a developmental venous anomaly identified by report and confirmed on review of the imaging. Thirty-one of the 580 controls (5.34%) had a developmental venous anomaly identified by report and confirmed on review of the imaging (P = .003). No statistically significant difference was noted in the prevalence of developmental venous anomalies among tumor types. No developmental venous anomaly drained the vascular territory of the tumor, and there was no correlation between the location of the developmental venous anomaly and the location of the neoplasm. CONCLUSIONS: The prevalence of developmental venous anomalies in this pediatric population with intracranial primary neoplasms is significantly greater than in those without neoplasms, suggesting an association that may be related to shared causative factors or susceptibilities to the development of these 2 separate entities.

Brain parenchymal signal abnormalities associated with developmental venous anomalies in children and young adults.

BACKGROUND AND PURPOSE: Abnormal signal in the drainage territory of developmental venous anomalies has been well described in adults but has been incompletely investigated in children. This study was performed to evaluate the prevalence of brain parenchymal abnormalities subjacent to developmental venous anomalies in children and young adults, correlating with subject age and developmental venous anomaly morphology and location. MATERIALS AND METHODS: Two hundred eighty-five patients with developmental venous anomalies identified on brain MR imaging with contrast, performed from November 2008 through November 2012, composed the study group. Data were collected for the following explanatory variables: subject demographics, developmental venous anomaly location, morphology, and associated parenchymal abnormalities. Associations between these variables and the presence of parenchymal signal abnormalities (response variable) were then determined. RESULTS: Of the 285 subjects identified, 172 met inclusion criteria, and among these subjects, 193 developmental venous anomalies were identified. Twenty-six (13.5%) of the 193 developmental venous anomalies had associated signal-intensity abnormalities in their drainage territory. After excluding developmental venous anomalies with coexisting cavernous malformations, we obtained an adjusted prevalence of 21/181 (11.6%) for associated signal-intensity abnormalities in developmental venous anomalies. Signal-intensity abnormalities were independently associated with younger subject age, cavernous malformations, parenchymal atrophy, and deep venous drainage of developmental venous anomalies. CONCLUSIONS: Signal-intensity abnormalities detectable by standard clinical MR images were identified in 11.6% of consecutively identified developmental venous anomalies. Signal abnormalities are more common in developmental venous anomalies with deep venous drainage, associated cavernous malformation and parenchymal atrophy, and younger subject age. The pathophysiology of these signal-intensity abnormalities remains unclear but may represent effects of delayed myelination and/or alterations in venous flow within the developmental venous anomaly drainage territory.

Elucidating the genetic basis of crystalline biofilm formation in Proteus mirabilis.

Proteus mirabilis forms extensive crystalline biofilms on urethral catheters that occlude urine flow and frequently complicate the management of long-term-catheterized patients. Here, using random transposon mutagenesis in conjunction with in vitro models of the catheterized urinary tract, we elucidate the mechanisms underpinning the formation of crystalline biofilms by P. mirabilis. Mutants identified as defective in blockage of urethral catheters had disruptions in genes involved in nitrogen metabolism and efflux systems but were unaffected in general growth, survival in bladder model systems, or the ability to elevate urinary pH. Imaging of biofilms directly on catheter surfaces, along with quantification of levels of encrustation and biomass, confirmed that the mutants were attenuated specifically in the ability to form crystalline biofilms compared with that of the wild type. However, the biofilm-deficient phenotype of these mutants was not due to deficiencies in attachment to catheter biomaterials, and defects in later stages of biofilm development were indicated. For one blocking-deficient mutant, the disrupted gene (encoding a putative multidrug efflux pump) was also found to be associated with susceptibility to fosfomycin, and loss of this system or general inhibition of efflux pumps increased sensitivity to this antibiotic. Furthermore, homologues of this system were found to be widely distributed among other common pathogens of the catheterized urinary tract. Overall, our findings provide fundamental new insight into crystalline biofilm formation by P. mirabilis, including the link between biofilm formation and antibiotic resistance in this organism, and indicate a potential role for efflux pump inhibitors in the treatment or prevention of P. mirabilis crystalline biofilms.

White matter microstructural abnormality in children with hydrocephalus detected by probabilistic diffusion tractography.

BACKGROUND AND PURPOSE: Hydrocephalus is a severe pathologic condition in which WM damage is a major factor associated with poor outcomes. The goal of the study was to investigate tract-based WM connectivity and DTI measurements in children with hydrocephalus by using the probabilistic diffusion tractography method. MATERIALS AND METHODS: Twelve children with hydrocephalus and 16 age-matched controls were included in the study. Probabilistic diffusion tractography was conducted to generate tract-based connectivity distribution and DTI measures for the genu of the corpus callosum and the connectivity index. Tract-based summary measurements, including the connectivity index and DTI measures (fractional anisotropy, mean diffusivity, axial diffusivity, and radial diffusivity), were calculated and compared between the 2 study groups. RESULTS: Tract-based summary measurement showed a higher percentage of voxels with lower normalized connectivity index values in the WM tracts in children with hydrocephalus. In the genu of the corpus callosum, the left midsegment of the corticospinal tract, and the right midsegment of the corticospinal tract, the normalized connectivity index value in children with hydrocephalus was found to be significantly lower (P < .05, corrected). The tract-based DTI measures showed that the children with hydrocephalus had significantly higher mean diffusivity, axial diffusivity, and radial diffusivity in the genu of the corpus callosum, left midsegment of the corticospinal tract, and right midsegment of corticospinal tract and lower fractional anisotropy in the genu of the corpus callosum (P < .05, corrected). CONCLUSIONS: The analysis of WM connectivity showed that the probabilistic diffusion tractography method is a sensitive tool to detect the decreased continuity in WM tracts that are under the direct influence of mechanical distortion and increased intracranial pressure in hydrocephalus. This voxel-based connectivity method can provide quantitative information complementary to the standard DTI summary measures.

DTI values in key white matter tracts from infancy through adolescence.

BACKGROUND AND PURPOSE: DTI is an advanced neuroimaging technique that allows in vivo quantification of water diffusion properties as surrogate markers of the integrity of WM microstructure. In our study, we investigated normative data from a large number of pediatric and adolescent participants to examine the developmental trends in DTI during this conspicuous WM maturation period. MATERIALS AND METHODS: DTI data in 202 healthy pediatric and adolescent participants were analyzed retrospectively. Fractional anisotropy and mean diffusivity values in the corpus callosum and internal capsule were fitted to an exponential regression model to delineate age-dependent maturational changes across the WM structures. RESULTS: The DTI metrics demonstrated characteristic exponential patterns of progression during development and conspicuous age-dependent changes in the first 36 months, with rostral WM tracts experiencing the highest slope of the exponential function. In contrast, the highest final FA and lowest MD values were detected in the splenium of the corpus callosum and the posterior limb of the internal capsule. CONCLUSIONS: Our analysis shows that the more caudal portions of the corpus callosum and internal capsule begin the maturation process earlier than the rostral regions, but the rostral regions develop at a more accelerated pace, which may suggest that rostral regions rely on development of more caudal brain regions to instigate their development. Our normative DTI can be used as a reference to study normal spatiotemporal developmental profiles in the WM and help identify abnormal WM structures in patient populations.

Diffusion tensor imaging properties and neurobehavioral outcomes in children with hydrocephalus.

BACKGROUND AND PURPOSE: White matter structural alterations and the correlation with neuropsychological deficits in children with hydrocephalus have not been well investigated. In this prospective study, the objectives were the following: 1) to apply DTI to detect in vivo white matter alterations based on diffusion properties in children with acute hydrocephalus, 2) to quantify early neuropsychological deficits, and 3) to explore the correlation between potential neuropsychological deficits and abnormalities in functionally related white matter. MATERIALS AND METHODS: A total of 44 children, 24 with hydrocephalus and 20 controls, were enrolled in the study. DTI indices, FA, MD, AD, and RD, were evaluated in the gCC, sCC, PLIC, and ALIC. The ABAS-II was used as a broad screener of development, including conceptual, social, practical, and motor skills. The correlation between the Motor Scale and DTI indices in the PLIC was analyzed. RESULTS: DTI analyses showed that the gCC and sCC in children with hydrocephalus had lower FA and higher MD, driven by the increased RD with statistical significance (P < .05) or trend-level significance (P = .06). The PLIC and ALIC had significantly higher AD in children with hydrocephalus (P < .05). On the ABAS-II, parent ratings of general adaptive skills, conceptual skills, and motor skills were significantly lower in children with hydrocephalus (all at P < .05). The MD and RD values in the PLIC were found to have trend-level or significant correlation with the Motor Scale (P = .057, .041, respectively). CONCLUSIONS: DTI reveals alterations in the white matter structure in children with hydrocephalus with preliminary findings suggesting correlation with clinical motor deficits.

Trainee misinterpretations on pediatric neuroimaging studies: classification, imaging analysis, and outcome assessment.

BACKGROUND AND PURPOSE: The scope of trainee misinterpretations on pediatric neuroimaging studies has been incompletely assessed. Our aim was to evaluate the frequency of trainee misinterpretations on neuroimaging exams in children, describe a useful classification system, and assess related patient management or outcome changes. MATERIALS AND METHODS: Pediatric neuroimaging examinations with trainee-dictated reports performed without initial attending radiologist assessment were evaluated for discrepant trainee interpretations by using a search of the RIS. The frequency of discrepant trainee interpretations was calculated and classified on the basis of the type of examination on which the error occurred, the specific type and severity of the discrepancy, and the effect on patient management and outcome. Differences relating to examination type and level of training were also assessed. RESULTS: There were 143 discrepancies on 3496 trainee-read examinations for a discrepancy rate of 4.1%. Most occurred on CT examinations (131; 92%). Most discrepancies (75) were minor but were related to the clinical presentation. Six were major and potentially life-threatening. Thirty-seven were overcalls. Most had no effect on clinical management (97, 68%) or resulted simply in clinical reassessment or imaging follow-up (43, 30%). There was no permanent morbidity or mortality related to the misinterpretations. The most common misinterpretations were related to fractures (28) and ICH (23). CT examinations of the face, orbits, and neck had the highest discrepancy rate (9.4%). Third- and fourth-year residents had a larger discrepancy rate than fellows. CONCLUSIONS: Trainee misinterpretations occur in 4.1% of pediatric neuroimaging examinations with only a small number being life-threatening (0.17%). Detailed analysis of the types of misinterpretations can be used to inform proactive trainee education.

Anisotropic diffusion properties in infants with hydrocephalus: a diffusion tensor imaging study.

BACKGROUND AND PURPOSE: Diffusion tensor imaging (DTI) can noninvasively detect in vivo white matter (WM) abnormalities on the basis of anisotropic diffusion properties. We analyzed DTI data retrospectively to quantify the abnormalities in different WM regions in children with hydrocephalus during early infancy. MATERIALS AND METHODS: Seventeen infants diagnosed with hydrocephalus (age range, 0.13-16.14 months) were evaluated with DTI and compared with 17 closely age-matched healthy children (age range, 0.20-16.11 months). Fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity, and radial diffusivity values in 5 regions of interest (ROIs) in the corpus callosum and internal capsule were measured and compared. The correlation between FA and age was also studied and compared by ROI between the 2 study groups. RESULTS: Infants with hydrocephalus had significantly lower FA, higher MD, and higher radial diffusivity values for all 3 ROIs in the corpus callosum, but not for the 2 ROIs in the internal capsule. In infants with hydrocephalus, the increase of FA with age during normal development was absent in the corpus callosum but was still preserved in the internal capsule. There was also a significant difference in the frequency of occurrence of abnormal FA values in the corpus callosum and internal capsule. CONCLUSIONS: This retrospective DTI study demonstrated significant WM abnormalities in infants with hydrocephalus in both the corpus callosum and internal capsule. The results also showed evidence that the impact of hydrocephalus on WM was different in the corpus callosum and internal capsule.

De novo cerebral arteriovenous malformation: case report and literature review.

We describe a rare case of a de novo cerebral arteriovenous malformation (AVM) in a 9-year-old girl. MR imaging at 6 years of age demonstrated band heterotopia. Follow-up MR imaging 3 years later demonstrated a new 3.5-cm AVM in the left parietol-occipital region, confirmed by conventional angiography. This report, along with limited previous reports, suggests that AVMs can be acquired lesions and that AVM development is a dynamic process extending into the postnatal period.

Large arachnoid granulations involving the dorsal superior sagittal sinus: findings on MR imaging and MR venography.

BACKGROUND AND PURPOSE: Large arachnoid granulations (AG) within the dorsal superior sagittal sinus (SSS) have been incompletely characterized and can be confused with pathology. This report reviews the characteristics of these anatomic structures to establish common imaging features that allow differentiation from pathology. MATERIALS AND METHODS: Twelve cases of large AG in the dorsal SSS are presented, identified by MR imaging. Signal intensity characteristics, size, location, venographic appearance, and association with adjacent venous and osseous structures were documented. RESULTS: A defect in the dura of the SSS was seen in all of the cases communicating with the subjacent subarachnoid space. The average size of the AG was 8.1 x 9.4 x 10.0 mm (range, 4-19 mm). Ten produced calvarial remodeling, and 11 were in the direct vicinity of the lambda. On T2-weighted images, all were hyperintense to the brain. On T1-weighted images, 8 were hypointense and 4 were hypointense with mixed areas of isointense signal intensity. All of the AGs were associated with cortical venous structures entering the sinus. On MR venography, AGs appeared as focal protrusions into the sinus, displacing, distorting, and narrowing the sinus lumen. Seven patients had headache without other visible cause on MR imaging, and 4 were initially interpreted as thrombosis or tumor. CONCLUSION: Large AGs can occur in the dorsal SSS. They are well-defined projections of the subarachnoid space into the sinus, can cause luminal narrowing and calvarial remodeling, and have typical signal intensity characteristics, position, and morphology differentiating them from other pathology. Association with patient symptoms is uncertain.

Diffusion tensor MR imaging reveals persistent white matter alteration after traumatic brain injury experienced during early childhood.

BACKGROUND AND PURPOSE: Diffusion tensor imaging (DTI) can noninvasively quantify white matter (WM) integrity. Although its application in adult traumatic brain injury (TBI) is common, few studies in children have been reported. The purposes of this study were to examine the alteration of fractional anisotropy (FA) in children with TBI experienced during early childhood and to quantify the association between FA and injury severity. MATERIALS AND METHODS: FA was assessed in 9 children with TBI (age = 7.89 +/- 1.00 years; Glasgow Coma Scale [GCS] = 10.11 +/- 4.68) and a control group of 12 children with orthopedic injuries without central nervous system involvement (age = 7.51 +/- 0.95 years). All of the subjects were at minimum 12 months after injury. We examined group differences in a series of predetermined WM regions of interest with t test analysis. We subsequently conducted a voxel-wise comparison with Spearman partial correlation analysis. Correlations between FA and injury severity were also calculated on a voxel-wise basis. RESULTS: FA values were significantly reduced in the TBI group in genu of corpus callosum (CC), posterior limb of internal capsule (PLIC), superior longitudinal fasciculus (SLF), superior fronto-occipital fasciculus (SFO), and centrum semiovale (CS). GCS scores were positively correlated with FA in several WM areas including CC, PLIC, SLF, CS, SFO, and inferior fronto-occipital fasciculus (IFO). CONCLUSION: This DTI study provides evidence that WM integrity remains abnormal in children with moderate-to-severe TBI experienced during early childhood and that injury severity correlated strongly with FA.

Using skimmed milk agar to functionally screen a gut metagenomic library for proteases may lead to false positives.

AIMS: Functional screens using skimmed-milk agar to obtain protease activity is a common approach. The aim of this study was to determine the efficacy of this screen to obtain protease activity from a metagenomic library. METHODS AND RESULTS: A distal gut metagenomic library was functionally screened using a skimmed-milk agar. The functional screen provided 231 clones generating the characteristic clear halo indicative of protease production. Clone analysis revealed that they were not protease-positive, but expressed glycosidic hydrolases and produced acid, which was responsible for the clear halos. CONCLUSIONS: The current skimmed-milk agar method to obtain proteases is not sufficiently robust to provide a definitive screen. Other- non-protease activities will also give the same clear halo and these would be interpreted as protease positive clones without further analysis. Hence a more robust buffered medium or a specific protein should be used. SIGNIFICANCE AND IMPACT OF THE STUDY: Functional screens are a powerful approach to obtaining enzymes from large metagenomic libraries and proteases are a particularly interesting target. The skimmed-milk agar is not sufficiently robust to ensure that only proteases are isolated and in order to save time and money this study has shown that better designed media can aid in the process.

Identification of an arteriovenous fistula in a child. Case report and review of the literature.

BACKGROUND: A 6-year-old girl sustained a subarachnoid hemorrhage after a mild head injury and was discovered to have an arteriovenous fistula (AVF). INVESTIGATIONS AND TREATMENT: The etiology of subarachnoid hemorrhage was not evident on the initial brain CT. Brain CT with CT angiography identified the lesion. The AVF was further imaged with brain MRI followed by cerebral angiography and successfully embolized. OUTCOME: The child did not suffer any neurological sequelae.

Magnetic resonance spectroscopy of the pediatric brain.

Proton magnetic resonance (MR) spectroscopy is a complementary method to MR imaging for understanding disease processes in the pediatric brain. By demonstrating the presence of various metabolites in the sampled tissue, MR spectroscopy helps in the understanding of abnormalities detected by MR imaging or clinical examination. This capability is especially pertinent in the pediatric brain, where the manifestation of pathology is superimposed upon a background of normal or abnormal brain development. In this article, we review the major metabolites demonstrated by MR spectroscopy and present examples of MR spectra obtained in various pathological processes encountered in children.

CT, MRI and MRS of Epstein-Barr virus infection: case report.

We report MRI and proton MR spectroscopy (MRS) findings in a 12-month-old girl with Epstein-Barr virus encephalitis. CT and MRI showed focal lesions in the basal ganglia. MRS of the lesions showed decreased N-acetyl aspartate and elevation of some amino acids, indicating an infectious rather than ischemic etiology. This case illustrates the use of MRS to narrow differential diagnosis.