Small extracellular particles with big potential for horizontal gene transfer: membrane vesicles and gene transfer agents

Bacteria are known to release different types of particles that serve various purposes such as the processing of metabolites, communication, and the transfer of genetic material. One of the most interesting aspects of the production of such particles is the biogenesis and trafficking of complex particles that can carry DNA, RNA, proteins or toxins into the surrounding environment to aid in bacterial survival or lead to gene transfer. Two important bacterial extracellular complexes are membrane vesicles and gene transfer agents. In this review, we will discuss the production, contents and functions of these two types of particles as related to their abilities to facilitate horizontal gene transfer.

Isolated lower extremity metastases, 9 years after initial diagnosis of retinoblastoma

We report the development of isolated lower extremity metastases, in a child, 9 years after her initial diagnosis and treatment of bilateral infantile retinoblastomas. The radiographic, scintigraphic, computed tomographic, and magnetic resonance imaging findings are discussed. The dominant metastatic focus was blastic, involving the medial cuneiform. Additional occult lesions were found in the base of the second metatarsal, middle cuneiform, navicular and tibial diaphysis. An open biopsy confirmed the diagnosis. The occurrence of late distant metastases is rare in the USA.

Imaging techniques used in the diagnosis, staging, and follow-up of patients with myeloma

Radiologists play a central role in the diagnosis, initial staging, follow-up, and restaging of patients with myeloma. This review article attempts to familiarize the reader with all the various types of myeloma, their imaging appearances and useful imaging strategies. The staging system for myeloma patients has been updated and now includes findings from advanced imaging modalities. Radiologists have a vast array of imaging modalities at their disposal to aid them in diagnosis, staging, and follow-up. Currently, conventional radiographic skeletal surveys, magnetic resonance imaging, and F-18 FDG PET/CT examinations are the most useful instruments.

Posterior-inferior glenoid rim shapes by MR imaging

Our purpose was to try to apply a CT classification of glenoid rim shapes to MR images and to determine the reliability of the subsequent MR classification by testing observer variability. Shoulder MR imaging exams of 54 consecutive patients were reviewed retrospectively by two musculoskeletal radiologists independently. Posterior-inferior glenoid rim shape was categorized, based on reported CT criteria, as triangle, "lazy-J" or "delta" using the most caudal MR section that unequivocally showed articular cartilage. The same studies were reviewed again one month later to test interobserver and intraobserver variability. Final determination of glenoid rim type was made by consensus. There were 31 males and 23 females with an average age of 42 years, range 14-75 years. Forty-one patients were referred for evaluation of nonspecific shoulder pain, 9 for suspected rotator cuff tear and 4 for instability. The most common shape was "lazy-J" with 32 patients (59%) having this type. The least common was delta shape, with 7 patients (13%) having this form. Fifteen patients (28%) had a normal triangle shape. There was significant interobserver variability in determining the shape of the glenoid rim with 17/54 (31%) discordant readings. For the "lazy-J" shape, the kappa value was .02, for the "delta" type, kappa value was .60 and for the triangle shape, kappa was .32. Intraobserver variability was 35% for radiologist A and 28% for radiologist B. Kappa values for intraobserver variability ranged from .53 to .85. Four patients had posterior instability, 3 were judged to have normal triangular inferior glenoid rims and 1 a "lazy J" type by Radiologist A. Radiologist B judged 2 of the instability patients as normal triangular and 2 as "lazy J". A CT classification of posterior-inferior glenoid rim shapes can be applied using MR imaging, however, there is significant observer variability that limits the applicability of this classification scheme with MR imaging.

An episodic outbreak of genetically related Burkholderia cepacia among non-cystic fibrosis patients at a university hospital

OBJECTIVE

To investigate an outbreak of Burkholderia cepacia.

DESIGN

Observational study and chart review.

PATIENTS

Adult non-cystic fibrosis (CF) patients.

SETTING

Intensive care units (ICUs) at a university-affiliated teaching hospital.

METHODS

As part of the epidemiological investigation, we conducted a chart review and collected environmental samples. A review of work schedules of healthcare workers also was performed. We used B. cepacia selective agar for preliminary screening for all isolates, which subsequently were confirmed as members of the B. cepacia complex by polyphasic analysis employing conventional biochemical reactions and genus- and species-specific polymerase chain reaction assays. Pulsed-field gel electrophoresis, randomly amplified polymorphic DNA typing, and automated ribotyping were used to genotype the isolates. As part of the intervention, contact isolation precautions were initiated for all patients identified as having had a culture positive for B. cepacia.

RESULTS

Between September 1997 and September 1999, B. cepacia was isolated from 31 adult patients without CF in ICUs at a university-affiliated teaching hospital. Based on geographic clustering and genotypic analysis, three distinct clusters were observed involving 20 patients. Isolates from 17 of these patients were available for testing and were found to be of the same strain (outbreak strain). Further taxonomic analysis indicated that the outbreak strain was B. cepacia complex genomovar III. Twelve (71%) of the 17 patients were judged to be infected, and 5 (29%) were colonized with this strain. Six of 200 environmental cultures from multiple sources in the hospital's ICUs yielded B. cepacia. Two of these isolates, both recovered from rooms of colonized patients, were the same genotype as the outbreak strain recovered from patients.

CONCLUSION

Despite an extensive investigation, the source of the B. cepacia clone involved in this outbreak remains unknown. The spatial and temporal pattern of cases suggests that cross-transmission of a genetically related strain contributed to clustering among patients. The initiation of contact isolation may have limited the extent of this transmission. Additional studies are needed to elucidate better the epidemiology of nosocomial B. cepacia infection among non-CF adult patients.

Hyperventilation, anxiety sensitivity, and the expectations for alcohol use: subjective and physiological reactivity to alcohol cues

The present study examined the relation between alcohol-related expectancies, body sensation fear and reactions to cues for alcohol following a hyperventilation task. Forty-two undergraduate students participated for course credit. Each student hyperventilated for 5 min, paced at a rate of 30 breaths per minute. Following hyperventilation, each student was exposed to containers with alcohol (beer and wine coolers), with subjective urge to consume and heart rate measures taken. Path analysis supported models associated with tension reduction and self-focused attention expectancies as significant contributors to increased urge to consume alcohol and lowered heart rate following hyperventilation. However, social-anxiety-related expectancies failed to demonstrate a relationship. These results suggest that additional work on the tension reduction model of alcohol use should examine physiological stressors in association with subject characteristics such as proneness to experience panic symptoms.

Ankle and foot trauma

This article reviews the most common foot and ankle injuries that the general radiologist and general orthopedic surgeon are likely to encounter. Fractures and dislocations seen in children and adults are included as well as soft tissue injuries. Ankle fracture classification schemes are discussed briefly. Techniques for advanced imaging with computed tomography (CT) and magnetic resonance (MR) are discussed where appropriate.

Myeloma and lymphoma

This article reviews current information regarding myeloma, especially multiple myeloma and plasmacytoma as well as primary lymphoma of bone (PLB). The emphasis is on diagnostic imaging, including radiography, computed tomography (CT), magnetic resonance (MR) imaging, and skeletal scintigraphy. Relevant clinical information, histologic findings, treatment, and outcome data are also discussed.

The search for a better treatment for recurrent Clostridium difficile disease: use of high-dose vancomycin combined with Saccharomyces boulardii

Recurrent Clostridium difficile disease (CDD) is a difficult clinical problem because antibiotic therapy often does not prevent further recurrences. In a previous study, the biotherapeutic agent Saccharomyces boulardii was used in combination with standard antibiotics and was found to be effective in reducing subsequent recurrences of CDD. In an effort to further refine a standard regimen, we tested patients receiving a regimen of a standard antibiotic for 10 days and then added either S. boulardii (1 g/day for 28 days) or placebo. A significant decrease in recurrences was observed only in patients treated with high-dose vancomycin (2 g/day) and S. boulardii (16.7%), compared with those who received high-dose vancomycin and placebo (50%; P=.05). No serious adverse reactions were observed in these patients. Comparison of data from this trial with data from previous studies indicates that recurrent CDD may respond to a short course of high-dose vancomycin or to longer courses of low-dose vancomycin when either is combined with S. boulardii.

Antibiotic levels in empyemic pleural fluid

OBJECTIVE

To determine the degree to which bioactive penicillin, metronidazole, ceftriaxone, clindamycin, vancomycin, and gentamicin penetrate into empyemic pleural fluid using our new rabbit model of empyema.

METHODS

An empyema was created via the intrapleural injection of 10(8)()Pasteurella multocida bacteria into the pleural space of New Zealand white rabbits. After an empyema was verified by thoracentesis and pleural fluid analysis, penicillin, 24,000 U/kg; metronidazole, 37 mg/kg; ceftriaxone, 30 mg/kg; clindamycin, 9 mg/kg; vancomycin, 15 mg/kg; or gentamicin, 1 mg/kg, were administered IV. Antibiotic levels in samples of pleural fluid and serum, collected serially for up to 480 min, were then determined using a bioassay.

RESULTS

The degree to which the different antibiotics penetrated into the infected pleural space was highly variable. Penicillin penetrated most easily, followed by metronidazole, ceftriaxone, clindamycin, vancomycin, and gentamicin. Of the antibiotics tested, penicillin and metronidazole equilibrated the most rapidly with the infected pleural fluid. Penicillin levels remained elevated in pleural fluid even after serum levels had decreased.

CONCLUSIONS

Using this rabbit model of empyema, there was marked variation in the penetration of antibiotics into the empyemic fluid. Although there are species differences between rabbit and human pleura, the variance in degree of penetration of antibiotics into the pleural space should be considered when antibiotics are selected for the treatment of patients with empyema.

The in vitro efficacy of varidase versus streptokinase or urokinase for liquefying thick purulent exudative material from loculated empyema

Patients with loculated parapneumonic effusion or empyema are sometimes treated with streptokinase or urokinase in an attempt to facilitate pleural fluid drainage by liquefying the pleural exudate and destroying the fibrin membranes producing the loculation. This study evaluated the effectiveness of streptokinase, urokinase, and Varidase (the combination of streptokinase and streptodornase) in liquefying gummy, purulent, exudative material from loculated empyemas. An empyema was created by injecting 10(8) Pasteurella multocida bacteria into the pleural space of New Zealand white rabbits. Twenty specimens, each containing 0.5 g of purulent material obtained 5 days after empyema induction, were placed in test tubes. Streptokinase (15,000 IU), urokinase (10,000 IU), Varidase (4,000-15,000 IU streptodornase + 15,000 IU streptokinase) or saline was added to five sets of four test tubes each. The amount of nonliquefied material that remained after incubation with the fibrinolytic agents was quantitated. Over the 6-h incubation period, the amount of nonliquefied material decreased from 0.5 g to 0.02 g in the Varidase group but never decreased to less than 0.4 g in any of the other three treatment groups. Liquefaction of thick pleural exudates from rabbits with empyema can be achieved with Varidase but not with streptokinase or urokinase.

Imaging features of primary lymphoma of bone

OBJECTIVE

Our objective was to describe the imaging appearances of primary lymphoma of bone, including conventional radiographic, scintigraphic, CT, and MR imaging features.

MATERIALS AND METHODS

We retrospectively reviewed 237 pathologically proven cases of primary lymphoma of bone. Evaluation included patient age, sex, lesion location, and pattern of bone destruction. Pathologic type, periosteal reaction, sequestrum, soft-tissue mass, extension across joints, and pathologic fracture were also noted.

RESULTS

The study population included 151 males and 86 females (ratio 1.8:1; range, 2-88 years; mean age, 42 years). Common locations were the distal femoral diametaphysis; proximal metadiaphysis of the tibia, femur, and humerus; and femoral mid shaft. Long bones were involved more often than flat bones (71% versus 22%). Common appearances were a lytic (70%) or mixed-density (28%) lesion with most cases showing a permeative or moth-eaten pattern (74%). Periosteal reaction was seen in 58% of the long bones. Sequestra were found in 37 patients (16%). Soft-tissue masses were present in 113 patients (48%). Extension across joints was seen in nine patients (4%). Pathologic fractures occurred in 53 patients (22%). Radionuclide (n = 56), CT (n = 45), and MR (n = 20) features were usually nonspecific. Pathologic types included non-Hodgkin's (n = 223) and Hodgkin's (n = 14) lymphoma.

CONCLUSION

Primary lymphoma of bone most often involves the diametaphysis of a major long bone and has an aggressive pattern of lytic bone destruction and associated soft-tissue mass. CT and MR imaging can suggest the diagnosis, particularly when a large soft-tissue mass and abnormal marrow attenuation or signal intensity is seen without extensive cortical destruction.

Small cell osteosarcoma of the ulna: a case report and review of the literature

We report a case of small cell osteosarcoma arising in the distal ulna. The radiologic and pathologic features of this histologic variant of osteosarcoma that allow differentiation from other lytic lesions with small round cells are discussed.

Classic adamantinoma in a 3-year-old

Classic adamantinoma of the long bones is a rare, low-grade malignant neoplasm arising most often in the tibia and usually in patients during the second to fifth decades. Although adamantinomas have been described in children, the histologic pattern in this age group is different from that seen in adults and resembles osteofibrous dysplasia. The usual pattern of adamantinoma in children has been termed "differentiated adamantinoma" and follows a benign course. We report a case of adamantinoma in the proximal tibia of a 3-year-old patient. The lesion had abundant epithelial component with formation of keratin pearls, a pattern that has been described only in classic adamantinoma occurring in adults. Since differentiated adamantinomas are essentially benign and classic adamantinomas are low-grade malignancies, the finding of a classic variant at this young age raised important therapeutic and prognostic issues.

Extra-articular triplane fracture of the distal tibia: a case report

The triplane fracture of the distal tibia is anatomically complex. It typically consists of a coronal fracture of the metaphysis, a transverse fracture of the physis, and a sagittal, intra-articular fracture of the epiphysis. We report an unusual variation of the triplane fracture which includes an extra-articular epiphyseal component involving the medial malleolus. This is an important variant to recognize because it does not disrupt the distal tibial articular surface. This lack of articular involvement allows for non-surgical management in contrast to the usual triplane fracture which often requires open reduction and internal fixation.

Preliminary findings of the international typing study on Clostridium difficile. International Clostridium Difficile Study Group

Preliminary results of the International Typing Study on Clostridium difficile indicate that there is excellent correlation between the phenotypic methods reliant on cell surface antigens for typing strains and that a larger number of phenotypes and genotypes of C. difficile exists than was previously appreciated by each group of investigators acting independently. Evidence has also emerged that some of the types described by each method are common to all typing methods, indicating that strains of the same type are found in hospitals in the United Kingdom, Belgium, the United States, and Australia.

Femoral sulcus angle measurements

We sought to determine whether the femoral sulcus angle measurement is consistent on different radiographic projections of the knee. Seventy-four cadaveric knees were radiographed using Merchant, Laurin, and Hughston projections. The measurements of the sulcus angle (mean, 138.6 degrees; SD, 6.9 degrees; and range, 120 degrees to 155 degrees) obtained with the Merchant technique were similar (P = 0.0007) to those obtained with the Hughston (mean, 137.4 degrees; SD, 7.6 degrees; range, 122 degrees to 155 degrees) and Laurin (mean, 141.6 degrees; SD, 6.9 degrees; and range, 125 degrees to 162 degrees) projections. Therefore, we submit that either the Hughston or Laurin view can be used instead of the Merchant view to reliably measure the femoral sulcus angle.

Recurrent Clostridium difficile diarrhea: characteristics of and risk factors for patients enrolled in a prospective, randomized, double-blinded trial

Recurrent Clostridium difficile diarrhea (RCDD) occurs in 20% of patients after they have received standard antibiotic treatment with vancomycin or metronidazole, but the reasons for the recurrences are largely unknown. Patients receiving vancomycin or metronidazole for active C. difficile diarrhea (CDD) were referred to our study centers for treatment and a 2-month follow-up as part of a randomized placebo-controlled trial. Sixty patients had RCDD (median number of episodes, 3.0; range, 2-9 episodes) and 64 were having their first episode of CDD. Patients with RCDD had more-severe abdominal pain and were more likely to have fever but initially responded well to antibiotic therapy. Data on sequential episodes showed no progression in disease severity. Five factors were associated with a higher risk of RCDD: the number of previous CDD episodes, onset of the initial disease in the spring, exposure to additional antibiotics for treatment of other infections, infection with immunoblot type 1 or 2 strains of C. difficile, and female gender. These factors may help to identify patients who are more likely to develop RCDD and require careful medical supervision.

Identification and characterization of a gene encoding a vertebrate-type carbonic anhydrase in cyanobacteria

A gene (designated ecaA) encoding a vertebrate-like (alpha-type) carbonic anhydrase (CA) has been isolated from two disparate cyanobacteria, Anabaena sp. strain PCC 7120 and Synechococcus sp. strain PCC 7942. The deduced amino acid sequences correspond to proteins of 29 and 26 kDa, respectively, and revealed significant sequence similarity to human CAI and CAII, as well as Chlamydomonas CAHI, including conservation of most active-site residues identified in the animal enzymes. Structural similarities between the animal and cyanobacterial enzymes extend to the levels of antigenicity, as the Anabaena protein cross-reacts with antisera derived against chicken CAII. Expression of the cyanobacterial ecaA is regulated by CO2 concentration and is highest in cells grown at elevated levels of CO2. Immunogold localization using an antibody derived against the ecaA protein indicated an extracellular location. Preliminary analysis of Synechococcus mutants in which ecaA has been inactivated by insertion of a drug resistance cassette suggests that extracellular carbonic anhydrase plays a role in inorganic-carbon accumulation by maintaining equilibrium levels of CO2 and HCO3- in the periplasm.

Pancreatic metastasis from Ewing's sarcoma

A 26-year-old man with Ewing's sarcoma of the femur was found to have a solitary visceral metastatic focus in the pancreas. This very unusual occurrence and the topic of metastases to the pancreas in general are discussed.

Increased incidence of Clostridium difficile-associated diarrhea following decreased restriction of antibiotic use

Removal of antimicrobial agents from formulary restriction status at our center was followed by an increase in the incidence of Clostridium difficile-associated diarrhea. The mean monthly incidence of C. difficile diarrhea for the 12-month period before institution of decreased restriction of antibiotic use was 3.4 infections per 1,000 admissions and rose to 6.2 infections per 1,000 admissions during the following 4-month period (P < .05). Patients who developed disease before and after decreased restriction of antibiotics were similar in terms of the mean number of antimicrobial agents administered and mean duration of therapy. The most commonly administered agents whose use preceded the onset of disease were cefazolin, trimethoprim-sulfamethoxazole, ampicillin, ticarcillin/clavulanate, and gentamicin (the latter drug was always used in combination with other agents). Immunoblot typing indicated that there was no association between C. difficile strains and administration of specific agents. There was no coincidental epidemic to account for the increased incidence of infection. The increased incidence of C. difficile disease is a potential problem that may occur following removal of extended-spectrum antimicrobial agents from formulary restriction status.

GlbN (cyanoglobin) is a peripheral membrane protein that is restricted to certain Nostoc spp

The glbN gene of Nostoc commune UTEX 584 is juxtaposed to nifU and nifH, and it encodes a 12-kDa monomeric hemoglobin that binds oxygen with high affinity. In N. commune UTEX 584, maximum accumulation of GlbN occurred in both the heterocysts and vegetative cells of nitrogen-fixing cultures when the rate of oxygen evolution was repressed to less than 25 micromol of O2 mg of chlorophyll a(-1) h(-1). Accumulation of GlbN coincided with maximum synthesis of NifH and ferredoxin NADP+ oxidoreductase (PetH or FNR). A total of 41 strains of cyanobacteria, including 40 nitrogen fixers and representing 16 genera within all five sections of the cyanobacteria were screened for the presence of glbN or GlbN. glbN was present in five Nostoc strains in a single copy. Genomic DNAs from 11 other Nostoc and Anabaena strains, including Anabaena sp. strain PCC 7120, provided no hybridization signals with a glbN probe. A constitutively expressed, 18-kDa protein which cross-reacted strongly with GlbN antibodies was detected in four Anabaena and Nostoc strains and in Trichodesmium thiebautii. The nifU-nifH intergenic region of Nostoc sp. strain MUN 8820 was sequenced (1,229 bp) and was approximately 95% identical to the equivalent region in N. commune UTEX 584. Each strand of the DNA from the nifU-nifH intergenic regions of both strains has the potential to fold into secondary structures in which more than 50% of the bases are internally paired. Mobility shift assays confirmed that NtcA (BifA) bound a site in the nifU-glbN intergenic region of N. commune UTEX 584 approximately 100 bases upstream from the translation initiation site of glbN. This site showed extensive sequence similarity with the promoter region of glnA from Synechococcus sp. strain PCC 7942. In vivo, GlbN had a specific and prominent subcellular location around the periphery of the cytosolic face of the cell membrane, and the protein was found solely in the soluble fraction of cell extracts. Our hypothesis is that GlbN scavenges oxygen for and is a component of a membrane-associated microaerobically induced terminal cytochrome oxidase.

Epidemiologic typing systems

Microbial strain typing is a useful adjunct to clinical epidemiology. Phenotypic typing systems examine expressed characteristics, whereas genotypic systems, including recent PCR-based systems, examine chromosomal or plasmid DNA. Typing systems have evaluated bacteria, fungi, and viruses successfully. The criteria used to assess the utility of each system include typeability, reproducibility, and discriminatory power.

Supramalleolar fatigue fractures of the tibia

OBJECTIVE

The objective of this paper is to describe fatigue fractures in the supramalleolar area of the tibia. The spectrum of imaging findings in 14 cases is presented, with emphasis on plain film radiographic findings.

DESIGN AND PATIENTS

Fourteen patients with fatigue fractures in the supramalleolar area of the distal tibia were seen in a 6-year period. The 13 men and 1 woman had an age range from 14 to 64 years (mean 30 years). These patients had no underlying conditions that would predispose them to fractures. Sequential plain film radiographs and other special imaging studies (technetium-99m scans and computed tomography) were retrospectively reviewed.

RESULTS AND CONCLUSIONS

Initial plain film radiographs showed a horizontal linear band of increased density in only 2 cases, a subtle cortical bulge in 5 cases, a focal "graying" of the cortex in 2 cases, a single layer periosteal reaction in 1 case, and no abnormality in the final 4 cases. Technetium-99m scans were done in 11 cases and showed focal areas of increased uptake in all 11. These areas of increased uptake were vertically orientated in 10. One patient had computed tomography showing cortical thickening around a linear lucency. The spectrum of imaging findings is similar to that seen in fatigue fractures in more common locations. Supramalleolar fatigue fractures should be suspected in patients who have pain in the distal tibia even when initial plain film radiographs are normal. When initial radiographs are normal, technetium-99m scans can confirm the diagnosis.

Serial pleural fluid analysis in a new experimental model of empyema

Prior attempts to create an animal model of empyema by direct inoculation of bacteria alone into the pleural space have been unsuccessful. The animals either died of overwhelming sepsis or cleared the infection from the pleural space without development of an empyema. We hypothesized that injection of bacteria with a nutrient agar into the pleural space would allow the bacteria to remain in the pleural space for an extended time period, permitting an empyema to develop. The bacterium Pasteurella multocida in brain heart infusion (BHI) agar was injected into the right hemithorax of 12 New Zealand white male rabbits. Our preliminary studies showed that the animals died in less than 7 days if they were not given parenteral antibiotics. For this reason, the rabbits were given penicillin, 200,000 U, IM, every 24 h starting 24 h after bacterial injection. Pleural fluid was sampled by thoracentesis at 12, 24, 48, 72, and 96 h after bacterial injection. Pleural fluid pH, glucose, lactate dehydrogenase (LDH), leukocyte count, and Gram's stain and culture (in one half of the animals) were obtained at each time point. Pleural biopsy specimens were obtained at autopsy after 96 h. The mean pleural fluid pH reached a nadir of 7.01 at 24 h and remained less than 7.1 throughout the experiment. The mean pleural fluid glucose level reached a nadir of 10 mg/dL at 24 h. The mean pleural fluid LDH peaked at 21,000 IU/L at 24 h and the mean pleural fluid leukocyte count peaked at 12 h with a value of 67,000 cells per cubic millimeter. Gram's stains revealed organisms and cultures were positive for growth in all animals at 12 and 24 h. Some animals had positive Gram's stains and growth on cultures up to 72 h after bacterial injection. At autopsy, all rabbits injected with bacteria had gross pus in the right pleural space and had developed a thick pleural peel. Microscopic specimens of the pleura revealed large numbers of leukocytes (primarily polymorphonuclear lymphocytes) with invasion of the adjacent lung and chest wall. In conclusion, this model more closely mimics the empyema that occurs in humans, relative to previous animal models. This model appears appropriate for additional randomized studies in which different methods for the treatment of empyema can be evaluated.

Clostridium difficile-associated diarrhea and colitis

OBJECTIVES

To review and summarize the status of diagnosis, epidemiology, infection control, and treatment of Clostridium difficile-associated disease (CDAD).

DIAGNOSIS

A case definition of CDAD should include the presence of symptoms (usually diarrhea) and at least one of the following positive tests: endoscopy revealing pseudomembranes, stool cytotoxicity test for toxin B, stool enzyme immunoassay for toxin A or B, or stool culture for C difficile (preferably with confirmation of organism toxicity if a direct stool toxin test is negative or not done). Testing of asymptomatic patients, including those who are asymptomatic after treatment, is not recommended other than for epidemiologic purposes. Lower gastrointestinal endoscopy is the only diagnostic test for pseudomembranous colitis, but it is expensive, invasive, and insensitive (51% to 55%) for the diagnosis of CDAD. Stool culture is the most sensitive laboratory test currently in clinical use, but it is not as specific as the cell cytotoxicity assay.

EPIDEMIOLOGY

C difficile is the most frequently identified cause of nosocomial diarrhea. The majority of C difficile infections are acquired nosocomially, and most patients remain asymptomatic following acquisition. Antimicrobial exposure is the greatest risk factor for patients, especially clindamycin, cephalosporins, and penicillins, although virtually every antimicrobial has been implicated. Cases of CDAD unassociated with prior antimicrobial or antineoplastic use are very rare. Hands of personnel, as well as a variety of environmental sites within institutions, have been found to be contaminated with C difficile, which can persist as spores for many months. Contaminated commodes, bathing tubs, and electronic thermometers have been implicated as sources of C difficile. Symptomatic and asymptomatic infected patients are the major reservoirs and sources for environmental contamination. Both genotypic and phenotypic typing systems for C difficile are available and have enhanced epidemiologic investigation greatly.

INFECTION CONTROL

Successful infection control measures designed to prevent horizontal transmission include the use of gloves in handling body substances and replacement of electronic thermometers with disposable devices. Isolation, cohorting, handwashing, environmental disinfection, and treatment of asymptomatic carriers are recommended practices for which convincing data of efficacy are not available. The most successful control measure directed at reduction in symptomatic disease has been antimicrobial restriction.

TREATMENT

Treatment of symptomatic (but not asymptomatic) patients with metronidazole or vancomycin for 10 days is effective; metronidazole may be preferred to reduce risk of vancomycin resistance among other organisms in hospitals. Recurrence of symptoms occurs in 7% to 20% of patients and is due to both relapse and reinfection. Over 90% of first recurrences can be treated successfully in the same manner as initial cases. Combination treatment with vancomycin plus rifampin or the addition orally of the yeast Saccharomyces boulardii to vancomycin or metronidazole treatment has been shown to prevent subsequent diarrhea in patients with recurrent disease.

Comparison of arbitrarily primed PCR with restriction endonuclease and immunoblot analyses for typing Clostridium difficile isolates

Arbitrarily primed PCR (AP-PCR) was used to genotype 26 clinical isolates of Clostridium difficile previously analyzed by immunoblotting (IB) and 20 isolates typed by restriction endonuclease analysis (REA) with HindIII. Two levels of differentiation were achieved with the AP-PCR approach by use of two different arbitrary primers. With the 19-mer arbitrary primer T-7 (first level of differentiation), a good correlation was found between IB and AP-PCR typing. Twenty isolates grouped into six IB types were separated into seven major AP-PCR types. These seven AP-PCR groups were further discriminated into 12 subtypes after genotyping with the arbitrary primer PG-05 (second level of differentiation). The remaining six isolates, all of different IB types, showed a unique and distinct DNA banding pattern with both of the arbitrary primers, T-7 and PG-05. Twenty isolates representing 20 REA types from 15 REA groups were resolved into 13 AP-PCR DNA profiles with the arbitrary primer T-7. A good correlation was found at this level of differentiation between the major REA groups, Y and M, and AP-PCR typing. While AP-PCR with this primer failed to differentiate isolates in REA groups J, G, R, and B, AP-PCR with PG-05 resolved these four isolates into four distinct AP-PCR types. In addition, one of three M strains and one of four Y strains displayed a slightly different DNA banding pattern by AP-PCR (with PG-05) from that of the other strains in the group. We conclude that AP-PCR is a rapid and sensitive method which not only complements other typing schemes but also may be a substitute and prove to be especially suited for immediate epidemiological tracking of nosocomial infections due to C. difficile.

Characterization of a nitrogen-fixation (nif) gene cluster from Anabaena azollae 1a shows that closely related cyanobacteria have highly variable but structured intergenic regions

The exact identity of cyanobacteria that have been cultured from symbiotic associations with the water fern Azolla spp., whether they are required in the symbiotic process, and their relationship to the symbiotic species, is a matter of some debate. We have characterized a 6 kb region containing the nifB operon and the nifH gene from cyanobacterium Anabaena azollae 1a, a putative symbiont of Azolla caroliniana. Five complete open reading frames have been sequenced. All are very highly conserved when compared with the corresponding regions of Anabaena sp. PCC 7120, with 93% to 97% identity at the nucleotide level and 93% to almost 100% at the amino-acid level. The intergenic regions, however, are not highly conserved (53-89% identity) when compared to the corresponding regions of Anabaena 7120: the A. azollae genome contains both more copies and more types of short tandemly repeated repetitive sequences than Anabaena 7120. The start points of transcription for both the nifB and nifH operons were mapped and found to be the same as those in Anabaena 7120. It was not possible to discern an improved consensus nif promoter sequence, but it was possible to define the likely extent of the promoter to within 40 bases upstream of the transcription start-point.

Clostridium difficile-associated diarrhea and colitis

OBJECTIVES

To review and summarize the status of diagnosis, epidemiology, infection control, and treatment of Clostridium difficile-associated disease (CDAD).

DIAGNOSIS

A case definition of CDAD should include the presence of symptoms (usually diarrhea) and at least one of the following positive tests: endoscopy revealing pseudomembranes, stool cytotoxicity test for toxin B, stool enzyme immunoassay for toxin A or B, or stool culture for C difficile (preferably with confirmation of organism toxicity if a direct stool toxin test is negative or not done). Testing of asymptomatic patients, including those who are asymptomatic after treatment, is not recommended other than for epidemiologic purposes. Lower gastrointestinal endoscopy is the only diagnostic test for pseudomembranous colitis, but it is expensive, invasive, and insensitive (51% to 55%) for the diagnosis of CDAD. Stool culture is the most sensitive laboratory test currently in clinical use, but it is not as specific as the cell cytotoxicity assay.

EPIDEMIOLOGY

C difficile is the most frequently identified cause of nosocomial diarrhea. The majority of C difficile infections are acquired nosocomially, and most patients remain asymptomatic following acquisition. Antimicrobial exposure is the greatest risk factor for patients, especially clindamycin, cephalosporins, and penicillins, although virtually every antimicrobial has been implicated. Cases of CDAD unassociated with prior antimicrobial or antineoplastic use are very rare. Hands of personnel, as well as a variety of environmental sites within institutions, have been found to be contaminated with C difficile, which can persist as spores for many months. Contaminated commodes, bathing tubs, and electronic thermometers have been implicated as sources of C difficile. Symptomatic and asymptomatic infected patients are the major reservoirs and sources for environmental contamination. Both genotypic and phenotypic typing systems for C difficile are available and have enhanced epidemiologic investigation greatly.

INFECTION CONTROL

Successful infection control measures designed to prevent horizontal transmission include the use of gloves in handling body substances and replacement of electronic thermometers with disposable devices. Isolation, cohorting, handwashing, environmental disinfection, and treatment of asymptomatic carriers are recommended practices for which convincing data of efficacy are not available. The most successful control measure directed at reduction in symptomatic disease has been antimicrobial restriction.

TREATMENT

Treatment of symptomatic (but not asymptomatic) patients with metronidazole or vancomycin for 10 days is effective; metronidazole may be preferred to reduce risk of vancomycin resistance among other organisms in hospitals. Recurrence of symptoms occurs in 7% to 20% of patients and is due to both relapse and reinfection. Over 90% of first recurrences can be treated successfully in the same manner as initial cases. Combination treatment with vancomycin plus rifampin or the addition orally of the yeast Saccharomyces boulardii to vancomycin or metronidazole treatment has been shown to prevent subsequent diarrhea in patients with recurrent disease.

In vivo stability and discriminatory power of methicillin-resistant Staphylococcus aureus typing by restriction endonuclease analysis of plasmid DNA compared with those of other molecular methods

We evaluated test discriminatory power and DNA type alterations among methicillin-resistant Staphylococcus aureus strains by testing 199 sequential isolates from 39 patients collected over 30 to 228 days. Isolates were typed by one or three different methods (restriction endonuclease analysis of plasmid DNA [REAP] with or without pulsed-field gel electrophoresis of genomic DNA [PFGE] and immunoblotting [IB]). REAP was highly discriminatory compared with PFGE and IB. However, the initial isolates from 4 of the 39 patients lacked detectable plasmid DNA and could not be typed by REAP. Typing of individual patient isolates showed that a different REAP type was identified only once every 138 days. Among 25 comparisons, seven sequential isolate pairs demonstrating REAP differences were also different by PFGE and IB. This likely represented the presence of more than one strain. Eighteen other pairs with REAP differences were identical or related to one another by PFGE and IB typing, and 17 of these differences were likely caused by a single genetic alteration within the same strain or clone. The rate of PFGE differences explicable by single genetic alterations among sequential isolates identical by REAP was similar to the overall rate for REAP differences in the whole collection. We conclude that REAP and PFGE typing differences explicable by single genetic alterations are relatively infrequent but not rare. These isolates should be examined by alternative typing systems to further support or refute clonality.

Clonal relationships among bloodstream isolates of Escherichia coli

The clonal relationships among 187 bloodstream isolates of Escherichia coli from 179 patients at Boston, Mass., Long Beach, Calif., and Nairobi, Kenya, were determined by multilocus enzyme electrophoresis (MLEE), analysis of polymorphisms associated with the ribosomal operon (ribotyping), and serotyping. MLEE based on 20 enzymes resolved 101 electrophoretic types (ETs), forming five clusters; ribotyping resolved 56 distinct patterns concordant with the analysis by MLEE. The isolates at each study site formed a genetically diverse group and demonstrated similar clonal structures, with the same small subset of lineages accounting for the majority of isolates at each site. Moreover, two ribotypes accounted for approximately 30% of the isolates at each study site. One cluster contained the majority (65%) of isolates and, by direct comparison of the ETs and ribotypes of individual isolates, was genetically indistinguishable from the largest cluster for each of two other collections of E. coli causing pyelonephritis and neonatal meningitis (R. K. Selander, T. K. Korhonen, V. Väisänen-Rhen, P. H. Williams, P. E. Pattison, and D. A. Caugent, Infect. Immun. 52:213-222, 1986; M. Arthur, C. E. Johnson, R. H. Rubin, R. D. Arbeit, C. Campanelli, C. Kim, S. Steinbach, M. Agarwal, R. Wilkinson, and R. Goldstein, Infect. Immun. 57:303-313, 1989), thus defining a virulent set of lineages. The isolates within these virulent lineages typically carried DNA homologous to the adhesin operon pap or sfa and the hemolysin operon hly and expressed O1, O2, O4, O6, O18, O25, or O75 antigens. DNA homologous to pap was distributed among isolates of each major cluster, whereas hly was restricted to isolates of two clusters, typically detected in pap-positive strains, and sfa was restricted to isolates of one cluster, typically detected in pap- and hly-positive strains. The occurrence of pap-positive isolates in the same geographically and genetically divergent lineages suggests that this operon was acquired early in the radiation of E. coli, while hly and sfa were acquired subsequently, most likely by pap-positive and pap- and hly-positive precursors, respectively.

The tibiofibular syndesmosis. Evaluation of the ligamentous structures, methods of fixation, and radiographic assessment

Twenty-five fresh-frozen cadaveric specimens were used to evaluate the role of the syndesmotic ligaments when the ankle is loaded with external rotation torque. An apparatus was constructed that allowed pure external-rotation torque to be applied through the ankle with the foot in neutral flexion. The apparatus provided solid fixation of the tibia while allowing free movement of the fibula in all planes. The syndesmotic ligaments were incrementally sectioned, and direct measurements of anatomical diastasis were made. Mortise and lateral radiographs were made at each increment under both loaded (5.0 newton-meters) and unloaded conditions. After all structures of the syndesmosis had been divided, the syndesmosis was reduced and was repaired with one or two screws. The strength of the repair was measured with incremental increases in torque of 1.0 newton-meter. The radiographs were measured by three independent observers in a blind fashion. In order to evaluate intraobserver error, each observer was randomly given forty radiographs to reinterpret. Diastasis and rotation were found to be related to the amount of injury of the ligament (p < 0.0001). After the entire syndesmosis had been divided, application of a 5.0-newton-meter torque resulted in a mean diastasis of 7.3 millimeters. The subsequent repair of the anterior tibiofibular ligament with suture failed at a mean of 2.0 newton-meters (range, 1.0 to 6.0 newton-meters) of torque. Repair with two screws was found to be stronger than repair with one, with the first construct failing at a mean of 11.0 newton-meters (range, 5.0 to 15.0 newton-meters) and the second, at a mean of 6.2 newton-meters (range, 2.0 to 10.0 newton-meters) (p = 0.0005). Failure of the screw fixation was not associated with the maximum previous diastasis (p = 0.13). Measurements of anatomical diastasis were compared with measurements made on the mortise and lateral radiographs. Measurements on the stress mortise radiographs had a weak correlation with diastasis (r = 0.41, p < 0.0001). However, measurements on the stress lateral radiographs had a higher correlation (r = 0.81, p < 0.0001). Additionally, interobserver correlation was significantly higher for the measurements on the lateral radiographs (r = 0.87, p < 0.0001) than for those on the mortise radiographs (r = 0.56, p < 0.0001). Intraobserver correlation for the three observers was poor with regard to the measurements on the mortise radiographs (r = 0.12, 0.42, and 0.25). The respective correlations for the measurements on the lateral radiographs were r = 0.81, 0.90, and 0.89.(ABSTRACT TRUNCATED AT 400 WORDS)

The "gray cortex ": an early sign of stress fracture

The purpose of this report is to describe an early radiographic sign of stress fracture, the "gray cortex ". The imaging findings in three patients with tibial stress fractures were reviewed. The "gray cortex " sign was evident on the initial conventional radiographs in all three cases. It was prospectively reported as a sign of stress fracture in two patients and was evident on the initial radiographs (taken elsewhere) of the third patient, who was referred for additional workup of a possible neoplasm. Special imaging studies (technetium-99m bone scan, computed tomography, and magnetic resonance imaging) confirmed the diagnosis in all three cases.

Gas bubbles in the hip joint on CT: an indication of recent dislocation

OBJECTIVE

The purpose of this study was to determine if gas bubbles in the hip joint seen on CT scans after trauma are reliable indicators of recent (< 48 hr) hip dislocation. We believe that the gas seen in the hip joint represents intracapsular nitrogen bubbles that result from the vacuum created by forcible distraction associated with traumatic dislocation.

MATERIALS AND METHODS

CT scans of 79 consecutive patients with pelvic injury were reviewed retrospectively. We noted the number and position of intracapsular gas bubbles, presence of joint effusion, soft-tissue injury, and associated fractures or dislocations. Intracapsular gas bubbles were defined as round areas of low attenuation, in an intracapsular position, that on visual inspection were equivalent to air. Seventy-three of 79 patients were imaged within 48 hr of injury. Most patients had been involved in a motor vehicle collision or were pedestrians struck by a motor vehicle. Fifteen patients had hip dislocation, including one patient with bilateral dislocation. Fifty-five patients had pelvic fractures without hip dislocation, and nine patients had soft-tissue injury without fracture or dislocation. Fourteen of 16 dislocations had been reduced at the time of scanning.

RESULTS

Gas bubbles were seen in the hip joint on CT scans in 13 (81%) of the 16 dislocated hips, including 12 (92%) of 13 dislocations in patients scanned within 4 hr of admission. Bubbles were present in 11 (79%) of 14 hip joints that had dislocations reduced at the time of scanning and in both hip joints that remained dislocated. Most bubbles were located anterior to the femoral neck; however, bubbles were also seen posteriorly. Bubble size (1-3 mm) and number (1-7) varied. Only two (3%) of 64 patients without dislocation had intracapsular gas bubbles; one had been shot and the other had extensive soft-tissue emphysema.

CONCLUSION

In the absence of penetrating trauma, intracapsular gas bubbles on CT are reliable indicators of recent hip dislocation and may be the only objective finding of this injury.

Characterization of RNA-binding protein genes in cyanobacteria

A number of genes that encode RNA-binding proteins belonging to the RNP family have been identified in cyanobacteria. All of them are predicted to encode small proteins with a single RNA recognition motif, containing both the RNP1 and RNP2 conserved motifs, and a short auxiliary motif which in many cases contains an abundance of glycine residues. Mutagenesis experiments to characterize the function of some of these gene products are being carried out. In Synechococcus sp. PCC 7942, interruption of the rbpA gene results in slower growth with an altered pigment composition.

Mycobacterium genavense infection presenting as a solitary brain mass in a patient with AIDS: case report and review

Patients with AIDS are prone to developing infections with opportunistic pathogens. Recently, a new mycobacterium, Mycobacterium genavense, has been found to cause infection in patients with AIDS. Previously published reports indicate that patients who are infected with this organism present with the same clinical features as do patients with disseminated infection due to organisms of the Mycobacterium avium complex. We describe an unusual case of a patient with AIDS who presented with grand mal seizures and a mass lesion in his brain, which was found to be caused by infection with M. genavense. No evidence of disseminated infection could be found in this patient. We discuss the microbiology of this organism and review the literature on M. genavense infections. Clinicians should be aware of this organism so that efforts at culture and identification will be made.

Nasal colonization with methicillin-resistant Staphylococcus aureus on admission to the surgical intensive care unit increases the risk of infection

We prospectively studied the relationship of perioperative methicillin-resistant Staphylococcus aureus (MRSA) nasal colonization and subsequent infection in surgical intensive care unit (SICU) patients. In addition, risk factors for MRSA nasal colonization were examined. All patients admitted to the 15-bed SICU between August 1991 and July 1992 had their anterior nares cultured. Cultures positive for S. aureus were subsequently placed on oxacillin-containing plates to screen for methicillin-resistance. Of 484 patients, 19 had MRSA nasal colonization (3.9%). There were five infections in the 19 patients with positive perioperative nasal cultures versus six infections in the remaining 465 patients (P < 0.0001). Immunoblot typing confirmed the concordance of colonizing and infecting strains. Prior exposure to the spinal cord injury center (P < 0.001) and prior antibiotic therapy (P < 0.003) were also significant multivariate risk factors for perioperative nasal colonization. Patients with perioperative MRSA nasal colonization are at significantly increased risk of subsequent postoperative MRSA infection.

Characterization of the genetic basis of antibiotic resistance in Clostridium difficile

By using dot blot hybridization, 69 of 102 Clostridium difficile isolates (68%) from the United States and other countries hybridized with at least one of nine DNA probes for erythromycin (Erm), tetracycline (Tet) or chloramphenicol (Cat) resistance determinants. The distribution of individual determinants in descending order of frequency was: Tet M, 32%; Erm Q, 25%; Erm FS, 18%; Tet P, 15%; Tet K, 15%; Cat P, 15%; Cat Q, 12%; Erm BP, 11%; Tet L, 7%. This is the first report of Tet P being carried by C. difficile and hitherto Erm FS has only been found within the genus Bacteriodes, while neither Tet K nor Tet L have been previously identified among the genus Clostridia. Eighteen percent of the hybridizing isolates carried multiple determinants coding for the same phenotype. A higher frequency of resistance genes was associated with prior exposure to antimicrobial agents, cytotoxin production and diarrhoea. Isolates recovered from bone marrow transplant patients carried significantly fewer antibiotic resistance genes than did those from immunocompetent general medicine patients. However, this may be due to the fact that each was located at a different site. Antibiotic resistance determinants may play a role in the virulence associated with C. difficile.

Recurrent Escherichia coli bacteremia

Escherichia coli is the most common gram-negative organism associated with bacteremia. While recurrent E. coli urinary tract infections are well-described, recurrent E. coli bacteremia appears to be uncommon, with no episodes noted in multiple series of patients with gram-negative bacteremias. We report on 5 patients with recurrent bloodstream infections identified from a series of 163 patients with E. coli bacteremia. For each patient, the isolates from each episode were analyzed by pulsed-field gel electrophoresis (PFGE) and ribotyping and for the presence of E. coli virulence factors. For each of four patients, the index and recurrent episodes of bacteremia represented the same strain as defined by PFGE, and the strains were found to carry one or more virulence factors. The remaining patient, with two episodes of bloodstream infection separated by a 4-year interval, was infected with two isolates that did not carry any virulence factors and that were clonally related by ribotype analysis but differed by PFGE. All five patients had either a local host defense defect (three patients) or impaired systemic defenses (one patient) or both (one patient). Thus, recurrent E. coli bacteremia is likely to represent a multifactorial process that occurs in patients with impaired host defenses who are infected with virulent isolates.