Genome sequencing and characterization of an extensively drug-resistant sequence type 111 serotype O12 hospital outbreak strain of Pseudomonas aeruginosa.

A series of extensively drug-resistant isolates of Pseudomonas aeruginosa from two outbreaks in UK hospitals were characterized by whole genome sequencing (WGS). Although these isolates were resistant to antibiotics other than colistin, we confirmed that they are still sensitive to disinfectants. The sequencing confirmed that isolates in the larger outbreak were serotype O12, and also revealed that they belonged to sequence type ST111, which is a major epidemic strain of P. aeruginosa throughout Europe. As this is the first reported sequence of an ST111 strain, the genome was examined in depth, focusing particularly on antibiotic resistance and potential virulence genes, and on the reported regions of genome plasticity. High degrees of sequence similarity were discovered between outbreak isolates collected from recently infected patients, isolates from sinks, an isolate from the sewer, and a historical isolate, suggesting that the ST111 strain has been endemic in the hospital for many years. The ability to translate easily from outbreak investigation to detailed genome biology by use of the same data demonstrates the flexibility of WGS application in a clinical setting.

Multidrug-resistant Pseudomonas aeruginosa outbreaks in two hospitals: association with contaminated hospital waste-water systems.

BACKGROUND: Multidrug-resistant Pseudomonas aeruginosa (MDR-P) expressing VIM-metallo-beta-lactamase is an emerging infection control problem. The source of many such infections is unclear, though there are reports of hospital outbreaks of P. aeruginosa related to environmental contamination, including tap water. AIM: We describe two outbreaks of MDR-P, sensitive only to colistin, in order to highlight the potential for hospital waste-water systems to harbour this organism. METHODS: The outbreaks were investigated by a combination of descriptive epidemiology, inspection and microbiological sampling of the environment, and molecular strain typing. FINDINGS: The outbreaks occurred in two English hospitals; each involved a distinct genotype of MDR-P. One outbreak was hospital-wide, involving 85 patients, and the other was limited to four cases in one specialized medical unit. Extensive environmental sampling in each outbreak yielded MDR-P only from the waste-water systems. Inspection of the environment and estates records revealed many factors that may have contributed to contamination of clinical areas, including faulty sink, shower and toilet design, clean items stored near sluices, and frequent blockages and leaks from waste pipes. Blockages were due to paper towels, patient wipes, or improper use of bedpan macerators. Control measures included replacing sinks and toilets with easier-to-clean models less prone to splashback, educating staff to reduce blockages and inappropriate storage, reviewing cleaning protocols, and reducing shower flow rates to reduce flooding. These measures were followed by significant reductions in cases. CONCLUSION: The outbreaks highlight the potential of hospital waste systems to act as a reservoir of MDR-P and other nosocomial pathogens.

Approaches to measure the fitness of Burkholderia cepacia complex isolates.

Members of the Burkholderia cepacia complex (Bcc) are highly resistant to many antibacterial agents and infection can be difficult to eradicate. A coordinated approach has been used to measure the fitness of Bcc bacteria isolated from cystic fibrosis (CF) patients with chronic Bcc infection using methods relevant to Bcc growth and survival conditions. Significant differences in growth rate were observed among isolates; slower growth rates were associated with isolates that exhibited higher MICs and were resistant to more antimicrobial classes. The nucleotide sequences of the quinolone resistance-determining region of gyrA in the isolates were determined and the ciprofloxacin MIC correlated with amino acid substitutions at codons 83 and 87. Biologically relevant methods for fitness measurement were developed and could be applied to investigate larger numbers of clinical isolates. These methods were determination of planktonic growth rate, biofilm formation, survival in water and survival during drying. We also describe a method to determine mutation rate in Bcc bacteria. Unlike in Pseudomonas aeruginosa where hypermutability has been detected in strains isolated from CF patients, we were unable to demonstrate hypermutability in this panel of Burkholderia cenocepacia and Burkholderia multivorans isolates.

Fluoroquinolone-resistant mutants of Burkholderia cepacia.

Fluoroquinolone-resistant Burkholderia cepacia mutants were selected on ciprofloxacin. The rate of mutation in gyrA was estimated to be 9.6 x 10(-11) mutations per division. Mutations in gyrA conferred 12- to 64-fold increases in MIC, and an additional parC mutation conferred a large increase in MIC (>256-fold). Growth rate, biofilm formation, and survival in water and during drying were not impaired in strains containing single gyrA mutations. Double mutants were impaired only in growth rate (0.85, relative to the susceptible parent).

Prospective evaluation of BDProbeTec strand displacement amplification (SDA) system for diagnosis of tuberculosis in non-respiratory and respiratory samples.

Nucleic acid amplification techniques (NAATs) have been demonstrated to make significant improvements in the diagnosis of tuberculosis (TB), particularly in the time to diagnosis and the diagnosis of smear-negative TB. The BD ProbeTec strand displacement amplification (SDA) system for the diagnosis of pulmonary and non-pulmonary tuberculosis was evaluated. A total of 689 samples were analysed from patients with clinically suspected TB. Compared with culture, the sensitivity and specificity for pulmonary samples were 98 and 89 %, and against final clinical diagnosis 93 and 92 %, respectively. This assay has undergone limited evaluation for non-respiratory samples and so 331 non-respiratory samples were tested, identifying those specimens that were likely to yield a useful result. These were CSF (n = 104), fine needle aspirates (n = 64) and pus (n = 41). Pleural fluid (n = 47) was identified as a poor specimen. A concern in using the SDA assay was that low-positive samples were difficult to interpret; 7.8 % of specimens fell into this category. Indeed, 64 % of the discrepant results, when compared to final clinical diagnosis, could be assigned as low-positive samples. Specimen type did not predict likelihood of a sample being in the low-positive zone. Although the manufacturers do not describe the concept of a low-positive zone, we have found that it aids clinical diagnosis.

Is computed tomographic grading of splenic injury useful in the nonsurgical management of blunt trauma?

Seventy adult and pediatric patients with blunt splenic injury were managed nonsurgically using previously published clinical criteria without regard to the appearance of the spleen on computed tomographic (CT) scans. Seven patients (10%) who underwent delayed surgery were considered failures of nonsurgical therapy; all recovered after total splenectomy. Two radiologists, blinded to patient outcome, retrospectively reviewed the admission CT scans of all 70 patients and graded them according to three published scoring systems. Higher grades of splenic injury on CT were not associated with an increased risk of failure (Fisher's exact test, p > 0.05). Nine of ten patients with very high scores on each of the scales were successfully managed without surgery; conversely, three patients with very low scores required urgent surgery. An elevated Injury Severity Score significantly increased the risk of failure of nonsurgical management (Chi-square test of trend, p = 0.001). No failures occurred in patients under age 17 years. Our data support the hypothesis that properly selected patients can be safely observed regardless of the magnitude of splenic injury on CT scans. A decision to undergo early exploration should be based on clinical criteria, including the patient's age and associated injuries.

Radiologic evaluation of tendon injuries.

This article reviews the imaging choices available to assess the tendons of the shoulder, knee, ankle, and wrist. Principles of tendon imaging and fundamental considerations of computer-derived image techniques are briefly discussed, with particular reference to magnetic resonance imaging. Although the criteria used to classify various tendon abnormalities are provided, the clinical role of imaging is emphasized.

Normal and abnormal glenoid labrum: assessment with multiplanar gradient-echo MR imaging.

A retrospective study of magnetic resonance (MR) imaging of the glenoid labrum performed with multiplanar gradient-echo (MPGR) sequences was done to ascertain the different appearances of the normal labrum and the findings in patients with tears. MPGR images were obtained with a 1.5-T magnet in 37 shoulders of 16 healthy subjects and 19 patients with subsequent surgical evaluation. Increased intralabral signal intensity was seen in 12 of 26 normal shoulders (46%), and atypical morphology was seen in six shoulders (23%). Atypical morphology was present in eight of nine patients with labral tears. Deformity (n = 2 [22%]) and clefts (n = 2 [22%]) were seen in patients with tears. Deformity (n = 3 [12%]) and clefts (n = 1 [4%]) were occasionally seen in healthy subjects. Absence of the labrum and separation of the labrum from the glenoid cavity was present only in patients with tears; therefore, the labrum should be presumed torn in the presence of these findings. Increased intralabral signal intensity on MPGR images did not help predict labral integrity; morphologic findings were more predictive of labral tear.

Follow-up of grade 2 meniscal abnormalities in the stable knee.

A prospective study of grade 2 meniscal abnormalities in patients with intact anterior cruciate ligaments was done to ascertain whether such lesions progress to complete tears. A follow-up magnetic resonance (MR) image was obtained in 22 patients in whom the initial MR image showed a grade 2 lesion in one or both menisci that had been proved at arthroscopy not to be torn. On the initial images, 27 menisci contained a grade 2 lesion. At follow-up, six of the 27 lesions appeared to have decreased in size (two had completely disappeared). Eighteen lesions appeared unchanged; only three had increased in size. The mean interval between the acquisition of initial and follow-up images was 27.3 months (range, 11-41 months). The two patients whose lesion disappeared were among the youngest patients evaluated. The three patients whose abnormality increased were slightly older and more active than average. The results suggest that in most patients grade 2 lesions are stable at up to 3 years follow-up.

Magnetic resonance imaging of the surgically repaired meniscus: six-month follow-up.

The appearance and rate of healing of sutured meniscal repairs in 17 patients were evaluated using magnetic resonance scans. While prior studies in animals and humans (1-4) suggest that complete healing can occur as early as 6 wk postoperatively, we found that at 7 wk 15/15 patients demonstrated meniscal defects at the site of repair. At 6 mo, 11/11 patients showed persistent signal abnormalities. Two patients scanned at 11-12 mo also had defects at the site of repair. Therefore, complete meniscal healing appears not to occur as early as previously believed. This may affect decisions regarding the type of suture material used, the surgical treatment of associated injuries and the postoperative rehabilitation regimen. As defects may be present for relatively long periods of time following meniscal repair, caution must be exercised when attempting to diagnose new or recurrent tears in these patients.

Technical variables influencing the detection of acute deep vein thrombosis by magnetic resonance imaging.

To establish which technical variables influence the detection of deep vein thrombosis by magnetic resonance imaging, 2 dogs, 5 normal volunteers and 17 patients were studied using a 1.5 T whole-body system. A sequential slice gradient echo acquisition (TR 25, TE 13, 0 = 30 degrees, 2 NEX, flow compensation rephasing gradients) in the axial plane was found to be optimal for detecting venous thrombosis. Thus, when using appropriate technique, MRI may identify deep venous thrombosis accurately. It may also allow the diagnosis of conditions which may simulate venous thrombosis clinically since the most common of these, ruptured Baker's cyst, cellulitis, muscle tear, hematoma and external venous compression are all readily identified by MRI.

The clinical significance of stage 2 meniscal abnormalities on magnetic resonance knee images.

The Stage 2 meniscal abnormality was subdivided into Stage 2A--linear abnormal signal not contacting an articular surface, Stage 2B--abnormal signal in contact with the articular surface on a single image, Stage 2C--extensive wedge-shaped signal abnormality not in contact with an articular surface. Arthroscopy showed tears in 2A 3%, 2B 0%, 2C 50%. Complete tears should only be diagnosed if contact is seen on more than one image. Many Stage 2C menisci may have tears.

A quantitative study of relaxation rate enhancement produced by iron oxide particles in polyacrylamide gels and tissue.

The proton relaxation rate enhancements produced by two types of iron oxide particles, M4125 and AM125 (Advanced Magnetics, Cambridge, MA) designed as potential MR contrast agents, have been measured in polyacrylamide gels and in liver and spleen. The organ uptakes, time courses, and biodistributions of these materials have been measured using radiolabeling. The relaxation rate enhancements produced by these particles have been related to the concentration of iron per gram material at different magnetic field strengths. The relaxation rates increase linearly as a function of concentration at field strengths varying from 0.15 to 7 T. The relaxation effects of these particles in tissue are significantly different from the behavior in vitro. These results suggest that several different mechanisms contribute to relaxation effects in the presence of iron oxide particles and they depend strongly on the way the particles are sequestered. Diffusion effects for a specified TE may be enhanced using gradient or single-spin echoes rather than multiple echoes. AM125 is significantly more effective as a relaxation agent than paramagnetic metal ions only at relatively high fields, while M4125 is less effective per unit concentration.

Quantitation of MR relaxation effects of iron oxide particles in liver and spleen.

The relaxation effects and organ distribution of superparamagnetic iron oxide particles for magnetic resonance imaging were measured in rats. T1 and T2 were measured for excised organs, and tissue iron levels were quantified with radiolabeling. Approximately 70% of the injected dose is present in the liver and 10% in the spleen 1 hour after injection. At 20 MHz, the doses required to reduce liver and spleen T2 to half the normal value, as measured with a Carr-Purcell-Meiboom-Gill sequence, were, respectively, 420 and 830 mumol iron injected per kilogram of rat. The transverse relaxation rates increase linearly with injected dose and showed no evidence of saturation. These results suggest that this material is less effective than previously suggested.

The detection of pulmonary emboli by magnetic resonance imaging. Evaluation of imaging parameters.

The authors studied the influence of gating, cardiac cycle, and timing of rephasing gradients upon the detection of pulmonary emboli by MRI. Serial single-section MR images were obtained in normal dogs and dogs with experimental pulmonary emboli. Images with cardiac gating, respiratory gating, and ungated images were obtained. Cardiac gating in systole and late magnetization rephasing had the best diagnostic accuracy. Gated images were clearly superior to ungated; with combined cardiac and respiratory gating, sensitivity was 82% and specificity 88%. These results are sufficiently promising to warrant further studies.

Radiographic differentiation between different etiologies of pulmonary edema.

We compared the plain chest radiographs of critically ill patients who had different types of pulmonary edema and evaluated the radiographs according to a standardized score sheet of findings. We included 94 total cases of pulmonary edema: 49 with cardiogenic, 33 with permeability, and 12 with renal/overhydration pulmonary edema. Patients with cardiogenic edema had enlarged hearts, vascular engorgement, septal lines, and absence of air bronchograms significantly more often than patients with permeability pulmonary edema. Renal/overhydration patients had enlarged hearts significantly more often than patients with permeability edema. There were no other statistically significant differences. Heart size and presence or absence of septal lines could have been used to distinguish cardiogenic and permeability edema in 83% of cases.

Radioisotope labeled platelets in medical diagnosis.

The myriad of applications of indium-111 labeled platelets (111In-P), both in biomedical research and clinical diagnostic imaging, in recent years is an index of the potential of this technology. Because many diseases involve the vascular system, a nontoxic platelet label suitable for imaging has immense potential for diagnosis. Presently confined to research centers, this technique is currently used in three main diagnostic situations: deep vein thrombosis, cardiac thrombi, and organ (renal) transplantation rejection. Future applications will proliferate when difficulties in achieving rapid labeling are overcome, and the period between study initiation and final diagnosis is diminished. This review emphasizes current clinical applications and the potential role of this technology in diagnostic imaging.

Indium-111 platelet scintigraphy for the diagnosis of acute venous thrombosis.

Platelets labeled with indium-111 have been used successfully as a marker of active thrombosis in man. To establish the diagnostic accuracy of platelet scintigraphy in comparison to contrast venography in the diagnosis of acute lower limb venous thrombosis, we evaluated 103 consecutive patients divided into two groups. Platelets were labeled by the indium-111 oxine method. Patients from group I (n = 73, 56 had venograms) were asymptomatic and underwent platelet scintigraphy 1.1 +/- 0.6 days (mean +/- 1 SD) after a major orthopedic procedure. Patients from group II (n = 30, all had venograms) were symptomatic and underwent platelet scintigraphy 1.2 +/- 1.7 days after venography. In group II, 15 patients with positive findings on contrast venography were treated with intravenous heparin; five others with positive venograms did not receive heparin until platelet scintigraphy was completed. Both platelet scintigraphy and contrast venography were evaluated by two blinded observers. Only studies with blinded agreement of both platelet scintigraphy and contrast venography were included in the analysis. Sensitivity and specificity of platelet scintigraphy for the whole limb were 93% and 97% in group I and 42% and 67% in group II. The lower sensitivity in group II was most likely attributable to therapy with heparin. These results demonstrate that platelet scintigraphy, a test that permits imaging for up to five days after a single injection, correlates favorably with contrast venography in patients who have not received heparin and may be used as a surveillance test in high-risk patients. The role of platelet scintigraphy in acutely symptomatic patients requires further evaluation.