National survey of infectious disease fellowship program directors: A call for subspecialized training in infection prevention and control and healthcare epidemiology

OBJECTIVE

The importance of infection prevention and control and healthcare epidemiology (IPC/HE) in healthcare facilities was highlighted during the COVID-19 pandemic. Infectious disease (ID) clinicians often hold leadership positions in IPC/HE teams; however, there is no standard for training or certification of ID physicians specializing in IPC/HE. We evaluated the current state of IPC/HE training in ID fellowship programs.

DESIGN

A national survey of ID fellowship program directors was conducted to assess current IPC/HE training components in programs and plans for expanded offerings.

SETTING AND PARTICIPANTS

All ID fellowship program directors in the United States and Puerto Rico.

METHODS

Surveys were distributed using Research Electronic Data Capture (REDCap) to program directors in March 2023, with 2 reminder emails; the survey closed after 4 weeks.

RESULTS

Of 166 program directors, 54 (32.5%) responded to the survey. Among respondent programs, 49 (90.7%) of 54 programs reported didactic training in IPC/HE averaging 4.4 hours over the course of the fellowship. Also, 18 (33.3%) of 54 reported a dedicated IPC/HE training track. Furthermore, 23 programs (42.6%) reported barriers to expanding training. There was support (n = 47, 87.0%) for formal IPC/HE certification from a professional society within the standard fellowship.

CONCLUSIONS

Despite the COVID-19 pandemic highlighting the need for ID medical doctors with IPC/HE expertise, formal training in ID fellowship remains limited. Most program directors support formalization of IPC/HE training by a professional organization. Creation of standardized advanced curriculums for ID fellowship training in IPC/HE could be considered by the Society of Healthcare Epidemiology of America (SHEA) to grow, retain, and enhance the IPC/HE physician workforce.

Neuroinvasive Bacillus cereus Infection in Immunocompromised Hosts: Epidemiologic Investigation of 5 Patients With Acute Myeloid Leukemia

Background

Bacillus cereus is a ubiquitous gram-positive rod-shaped bacterium that can cause sepsis and neuroinvasive disease in patients with acute leukemia or neutropenia.

Methods

A single-center retrospective review was conducted to evaluate patients with acute leukemia, positive blood or cerebrospinal fluid test results for B cereus, and abnormal neuroradiographic findings between January 2018 and October 2022. Infection control practices were observed, environmental samples obtained, a dietary case-control study completed, and whole genome sequencing performed on environmental and clinical Bacillus isolates.

Results

Five patients with B cereus neuroinvasive disease were identified. All patients had acute myeloid leukemia (AML), were receiving induction chemotherapy, and were neutropenic. Neurologic involvement included subarachnoid or intraparenchymal hemorrhage or brain abscess. All patients were treated with ciprofloxacin and survived with limited or no neurologic sequelae. B cereus was identified in 7 of 61 environmental samples and 1 of 19 dietary protein samples-these were unrelated to clinical isolates via sequencing. No point source was identified. Ciprofloxacin was added to the empiric antimicrobial regimen for patients with AML and prolonged or recurrent neutropenic fevers; no new cases were identified in the ensuing year.

Conclusions

B cereus is ubiquitous in the hospital environment, at times leading to clusters with unrelated isolates. Fastidious infection control practices addressing a range of possible exposures are warranted, but their efficacy is unknown and they may not be sufficient to prevent all infections. Thus, including B cereus coverage in empiric regimens for patients with AML and persistent neutropenic fever may limit the morbidity of this pathogen.

A decade of clinical microbiology: top 10 advances in 10 years: what every infection preventionist and antimicrobial steward should know

The past 10 years have brought paradigm-shifting changes to clinical microbiology. This paper explores the top 10 transformative innovations across the diagnostic spectrum, including not only state of the art technologies but also preanalytic and post-analytic advances. Clinical decision support tools have reshaped testing practices, curbing unnecessary tests. Innovations like broad-range polymerase chain reaction and metagenomic sequencing, whole genome sequencing, multiplex molecular panels, rapid phenotypic susceptibility testing, and matrix-assisted laser desorption ionization time-of-flight mass spectrometry have all expanded our diagnostic armamentarium. Rapid home-based testing has made diagnostic testing more accessible than ever. Enhancements to clinician-laboratory interfaces allow for automated stewardship interventions and education. Laboratory restructuring and consolidation efforts are reshaping the field of microbiology, presenting both opportunities and challenges for the future of clinical microbiology laboratories. Here, we review key innovations of the last decade.

If you don't test, they will not treat: Impact of stopping preoperative screening for asymptomatic bacteriuria

Objective

Screening for asymptomatic bacteriuria (ASB) is not recommended outside of patients undergoing invasive urological procedures and during pregnancy. Despite national guidelines recommending against screening for ASB, this practice is prevalent. We present outcomes from a quality-improvement intervention targeting patients undergoing cardiac artery bypass grafting surgery (CABG) at Massachusetts General Hospital, a tertiary-care hospital in Boston, Massachusetts, where preoperative testing checklists were modified to remove routine urinalysis and urine culture. This was a before-and-after intervention study.

Methods

Prior to the intervention, screening for ASB was included in the preoperative check list for all patients undergoing CABG. We assessed the proportion of patients undergoing screening for ASB in the 6 months prior to and after the intervention. We estimated cost savings from averted laboratory analyses, and we evaluated changes in antibiotic prescriptions. We additionally examined the incidence of postoperative surgical-site infections (SSIs), central-line-associated bloodstream infections (CLABSIs), catheter-associated urinary tract infections (CAUTIs) and Clostridioides difficile infections (CDIs).

Results

Comparing the pre- and postintervention periods, urinalyses decreased by 76.5% and urine cultures decreased by 87.0%, with an estimated cost savings of $8,090.38. There were 50% fewer antibiotic prescriptions for bacteriuria after the intervention.

Conclusions

Removal of urinalysis and urine culture from preoperative checklists for cardiac surgery led to a statistically significant decrease in testing without an increase in SSIs, CLABSIs, CAUTIs, or CDI. Challenges identified included persistence of checklists in templated order sets in the electronic health record.

Infection Prevention and Control of Severe Acute Respiratory Syndrome Coronavirus 2 in Health Care Settings

The authors describe infection prevention and control approaches to severe acute respiratory syndrome coronavirus 2 in the health care setting, including a review of the chain of transmission and the hierarchy of controls, which are cornerstones of infection control and prevention. The authors also discuss lessons learned from nosocomial transmission events.

Ceftazidime-Avibactam in Combination With Fosfomycin: A Novel Therapeutic Strategy Against Multidrug-Resistant Pseudomonas aeruginosa

Previously, by targeting penicillin-binding protein 3, Pseudomonas-derived cephalosporinase (PDC), and MurA with ceftazidime-avibactam-fosfomycin, antimicrobial susceptibility was restored among multidrug-resistant (MDR) Pseudomonas aeruginosa. Herein, ceftazidime-avibactam-fosfomycin combination therapy against MDR P. aeruginosa clinical isolate CL232 was further evaluated. Checkerboard susceptibility analysis revealed synergy between ceftazidime-avibactam and fosfomycin. Accordingly, the resistance elements present and expressed in P. aeruginosa were analyzed using whole-genome sequencing and transcriptome profiling. Mutations in genes that are known to contribute to β-lactam resistance were identified. Moreover, expression of blaPDC, the mexAB-oprM efflux pump, and murA were upregulated. When fosfomycin was administered alone, the frequency of mutations conferring resistance was high; however, coadministration of fosfomycin with ceftazidime-avibactam yielded a lower frequency of resistance mutations. In a murine infection model using a high bacterial burden, ceftazidime-avibactam-fosfomycin significantly reduced the P. aeruginosa colony-forming units (CFUs), by approximately 2 and 5 logs, compared with stasis and in the vehicle-treated control, respectively. Administration of ceftazidime-avibactam and fosfomycin separately significantly increased CFUs, by approximately 3 logs and 1 log, respectively, compared with the number at stasis, and only reduced CFUs by approximately 1 log and 2 logs, respectively, compared with the number in the vehicle-treated control. Thus, the combination of ceftazidime-avibactam-fosfomycin was superior to either drug alone. By employing a "mechanism-based approach" to combination chemotherapy, we show that ceftazidime-avibactam-fosfomycin has the potential to offer infected patients with high bacterial burdens a therapeutic hope against infection with MDR P. aeruginosa that lack metallo-β-lactamases.

2385. Ceftazidime–Avibactam in Combination With Fosfomycin: A Novel Therapeutic Strategy Against Multidrug-Resistant Pseudomonas aeruginosa

Background

By targeting penicillin binding protein-3, the AmpC β-lactamase, and MurA, another enzyme involved in cell wall synthesis, with the ceftazidime–avibactam–fosfomycin combination, we previously overcame multidrug resistance (MDR) in vitro in an archived collection of Pseudomonas aeruginosa clinical isolates. Here, we further validate the ceftazidime–avibactam–fosfomycin combination using the MDR P. aeruginosa clinical isolate, CL232.

Methods

Whole genome and transcriptome sequencing, checkerboard analysis, and determination of mutation frequency as well as mutation prevention concentration were conducted. In addition, the ceftazidime–avibactam–fosfomycin combination was tested in a neutropenic thigh murine infection model with a high bacterial burden (2 × 10⁷ colony forming units (CFUs)) of MDR P. aeruginosa clinical isolate CL232.

Results

Checkerboard analysis revealed slight synergy with fractional inhibitory concentration index of 0.53 for 25–6.25 μg/mL of ceftazidime–avibactam combined with 12.5 μg/mL of fosfomycin. Accordingly, the resistance elements in P. aeruginosa CL232 were analyzed via whole-genome sequencing (WGS) and transcriptome sequencing (RNAseq). WGS of CL232 revealed mutations in genes (e.g., oprD, ampR) that contribute to β-lactam resistance. Moreover, expression of the AmpC β-lactamase and the MexAB-OprM efflux pump were upregulated (~2–6-fold). The potential for the development of ceftazidime–avibactam-fosfomycin resistance was assessed in vitro. Fosfomycin alone was found to have a high mutation frequency 1.9 × 10⁻⁵; however, the addition of ceftazidime–avibactam reduced this frequency by 3-logs. In addition, the ceftazidime–avibactam–fosfomycin combination possessed the lowest mutation prevention concentration at 64 mg/L–4 mg/L–64 mg/L. In a neutropenic thigh murine infection model, the ceftazidime–avibactam–fosfomycin combination was found to reduce CFUs by 5–6 logs compared with vehicle-treated mice, while ceftazidime–avibactam and fosfomycin dosed separately decreased CFUs by ~1 log and 2–3 logs, respectively.

Conclusion

The combination of ceftazidime–avibactam–fosfomycin is highly likely to offer patients who suffer from infections with a high bacteria burdens (i.e., pneumonia) a therapeutic hope against MDR P. aeruginosa.

Disclosures

K. M. Papp-Wallace, F. Hoffmann-La Roche Ltd: Grant Investigator, Research grant. E. J. Ellis-Grosse, Zavante Therapeutics, Inc.,: Employee and Shareholder, Salary.

Overcoming an Extremely Drug Resistant (XDR) Pathogen: Avibactam Restores Susceptibility to Ceftazidime for Burkholderia cepacia Complex Isolates from Cystic Fibrosis Patients

Burkholderia multivorans is a significant health threat to persons with cystic fibrosis (CF). Infections are difficult to treat as this pathogen is inherently resistant to multiple antibiotics. Susceptibility testing of isolates obtained from CF respiratory cultures revealed that single agents selected from different antibiotic classes were unable to inhibit growth. However, all isolates were found to be susceptible to ceftazidime when combined with the novel non-β-lactam β-lactamase inhibitor, avibactam (all minimum inhibitor concentrations (MICs) were ≤8 mg/L of ceftazidime and 4 mg/L of avibactam). Furthermore, a major β-lactam resistance determinant expressed in B. multivorans, the class A carbapenemase, PenA was readily inhibited by avibactam with a high k₂/K of (2 ± 1) × 10⁶ μM^-1 s^-1 and a slow k_off of (2 ± 1) × 10^-3 s^-1. Mass spectrometry revealed that avibactam formed a stable complex with PenA for up to 24 h and that avibactam recyclized off of PenA, re-forming the active compound. Crystallographic analysis of PenA-avibactam revealed several interactions that stabilized the acyl-enzyme complex. The deacylation water molecule possessed decreased nucleophilicity, preventing decarbamylation. In addition, the hydrogen-bonding interactions with Lys-73 were suggestive of a protonated state. Thus, Lys-73 was unlikely to abstract a proton from Ser-130 to initiate recyclization. Using Galleria mellonella larvae as a model for infection, ceftazidime-avibactam was shown to significantly (p < 0.001) improve survival of larvae infected with B. multivorans. To further support the translational impact, the ceftazidime-avibactam combination was evaluated using susceptibility testing against other strains of Burkholderia spp. that commonly infect individuals with CF, and 90% of the isolates were susceptible to the combination. In summary, ceftazidime-avibactam may serve as a preferred therapy for people that have CF and develop Burkholderia spp. infections and should be considered for clinical trials.

SHV-129: A Gateway to Global Suppressors in the SHV β-Lactamase Family?

Enzymes are continually evolving in response to environmental pressures. In order to increase enzyme fitness, amino acid substitutions can occur leading to a changing function or an increased stability. These evolutionary drivers determine the activity of an enzyme and its success in future generations in response to changing conditions such as environmental stressors or to improve physiological function allowing continual persistence of the enzyme. With recent warning reports on antibiotic resistance and multidrug resistant bacterial infections, understanding the evolution of β-lactamase enzymes, which are a large contributor to antibiotic resistance, is increasingly important. Here, we investigated a variant of the SHV β-lactamase identified from a clinical isolate of Escherichia coli in 2011 (SHV-129, G238S-E240K-R275L-N276D) to identify the first instance of a global suppressor substitution in the SHV β-lactamase family. We have used this enzyme to show that several evolutionary principles are conserved in different class A β-lactamases, such as active site mutations reducing stability and requiring compensating suppressor substitutions in order to ensure evolutionary persistence of a given β-lactamase. However, the pathway taken by a given β-lactamase in order to reach its evolutionary peak under a given set of conditions is likely different. We also provide further evidence for a conserved stabilizing substitution among class A β-lactamases, the back to consensus M182T substitution. In addition to expanding the spectrum of β-lactamase activity to include the hydrolysis of cefepime, the amino acid substitutions found in SHV-129 provide the enzyme with an excess of stability, which expands the evolutionary landscape of this enzyme and may result in further evolution to potentially include resistance to carbapenems or β-lactamase inhibitors.

Activity of ceftazidime/avibactam against isogenic strains of Escherichia coli containing KPC and SHV β-lactamases with single amino acid substitutions in the Ω-loop

OBJECTIVES

The objective of this study was to explore the activity of ceftazidime and ceftazidime/avibactam against a collection of isogenic strains of Escherichia coli DH10B possessing SHV and KPC β-lactamases containing single amino acid substitutions in the Ω-loop (residues 164-179).

METHODS

Ceftazidime and ceftazidime/avibactam MICs were determined by the agar dilution method for a panel of isogenic E. coli strains expressing SHV-1 and KPC-2 with amino acid substitutions at positions 164, 167, 169 or 179. Two KPC-2 β-lactamase variants that possessed elevated MICs of ceftazidime/avibactam were selected for further biochemical analyses.

RESULTS

Avibactam restored susceptibility to ceftazidime for all Ω-loop variants of SHV-1 with MICs <8 mg/L. In contrast, several of the Arg164 and Asp179 variants of KPC-2 demonstrated MICs of ceftazidime/avibactam >8 mg/L. β-Lactamase kinetics showed that the Asp179Asn variant of KPC-2 demonstrated enhanced kinetic properties against ceftazidime. The Ki app, k2/K and koff of the Arg164Ala and Asp179Asn variant KPC-2 β-lactamases indicated that avibactam effectively inhibited these enzymes.

CONCLUSIONS

Several KPC-2 variants demonstrating ceftazidime resistance as a result of single amino acid substitutions in the Ω-loop were not susceptible to ceftazidime/avibactam (MICs >8 mg/L). We hypothesize that this observation is due to the stabilizing interactions (e.g. hydrogen bonds) of ceftazidime within the active site of variant β-lactamases that prevent avibactam from binding to and inhibiting the β-lactamase. As ceftazidime/avibactam is introduced into the clinic, monitoring for new KPC-2 variants that may exhibit increased ceftazidime kinetics as well as resistance to this novel antibiotic combination will be important.

Activities of ceftazidime, ceftaroline, and aztreonam alone and combined with avibactam against isogenic Escherichia coli strains expressing selected single β-lactamases

Avibactam is a novel β-lactamase inhibitor that restores the activity of otherwise hydrolyzed β-lactams against Gram-negative bacteria expressing different classes of serine β-lactamases. In the last decade, β-lactam-avibactam combinations were tested against a variety of clinical isolates expressing multiple commonly encountered β-lactamases. Here, we analyzed isogenic Escherichia coli strains expressing selected single β-lactamase genes that were not previously tested or were not characterized in an isogenic background. The activities of ceftazidime, ceftaroline, and aztreonam alone and in combination with 4 mg/L of avibactam, as well as comparator agents, were assessed against a unique collection of isogenic strains of E. coli carrying selected extended-spectrum, inhibitor-resistant, and/or carbapenem-hydrolyzing bla genes. When combined with avibactam, ceftazidime, ceftaroline, or aztreonam MICs were reduced for 91.4%, 80.0%, and 80.0% of isolates, respectively. The data presented add to our understanding of the microbiologic spectrum of these β-lactams with avibactam and serve as a reference for further studies.

Unexpected challenges in treating multidrug-resistant Gram-negative bacteria: resistance to ceftazidime-avibactam in archived isolates of Pseudomonas aeruginosa

Pseudomonas aeruginosa is a notoriously difficult-to-treat pathogen that is a common cause of severe nosocomial infections. Investigating a collection of β-lactam-resistant P. aeruginosa clinical isolates from a decade ago, we uncovered resistance to ceftazidime-avibactam, a novel β-lactam/β-lactamase inhibitor combination. The isolates were systematically analyzed through a variety of genetic, biochemical, genomic, and microbiological methods to understand how resistance manifests to a unique drug combination that is not yet clinically released. We discovered that avibactam was able to inactivate different AmpC β-lactamase enzymes and that blaPDC regulatory elements and penicillin-binding protein differences did not contribute in a major way to resistance. By using carefully selected combinations of antimicrobial agents, we deduced that the greatest barrier to ceftazidime-avibactam is membrane permeability and drug efflux. To overcome the constellation of resistance determinants, we show that a combination of antimicrobial agents (ceftazidime/avibactam/fosfomycin) targeting multiple cell wall synthetic pathways can restore susceptibility. In P. aeruginosa, efflux, as a general mechanism of resistance, may pose the greatest challenge to future antibiotic development. Our unexpected findings create concern that even the development of antimicrobial agents targeted for the treatment of multidrug-resistant bacteria may encounter clinically important resistance. Antibiotic therapy in the future must consider these factors.

Current and emerging MR imaging techniques for the diagnosis and management of CSF flow disorders: a review of phase-contrast and time-spatial labeling inversion pulse

This article provides an overview of phase-contrast and time-spatial labeling inversion pulse MR imaging techniques to assess CSF movement in the CNS under normal and pathophysiologic situations. Phase-contrast can quantitatively measure stroke volume in selected regions, notably the aqueduct of Sylvius, synchronized to the heartbeat. Judicious fine-tuning of the technique is needed to achieve maximal temporal resolution, and it has limited visualization of CSF motion in many CNS regions. Phase-contrast is frequently used to evaluate those patients with suspected normal pressure hydrocephalus and a Chiari I malformation. Correlation with successful treatment outcome has been problematic. Time-spatial labeling inversion pulse, with a high signal-to-noise ratio, assesses linear and turbulent motion of CSF anywhere in the CNS. Time-spatial labeling inversion pulse can qualitatively visualize whether CSF flows between 2 compartments and determine whether there is flow through the aqueduct of Sylvius or a new surgically created stoma. Cine images reveal CSF linear and turbulent flow patterns.

Penam sulfones and β-lactamase inhibition: SA2-13 and the importance of the C2 side chain length and composition

β-Lactamases are the major reason β-lactam resistance is seen in Gram-negative bacteria. To combat this resistance mechanism, β-lactamase inhibitors are currently being developed. Presently, there are only three that are in clinical use (clavulanate, sulbactam and tazobactam). In order to address this important medical need, we explored a new inhibition strategy that takes advantage of a long-lived inhibitory trans-enamine intermediate. SA2-13 was previously synthesized and shown to have a lower k(react) than tazobactam. We investigated here the importance of the carboxyl linker length and composition by synthesizing three analogs of SA2-13 (PSR-4-157, PSR-4-155, and PSR-3-226). All SA2-13 analogs yielded higher turnover numbers and k(react) compared to SA2-13. We next demonstrated using protein crystallography that increasing the linker length by one carbon allowed for better capture of a trans-enamine intermediate; in contrast, this trans-enamine intermediate did not occur when the C2 linker length was decreased by one carbon. If the linker was altered by both shortening it and changing the carboxyl moiety into a neutral amide moiety, the stable trans-enamine intermediate in wt SHV-1 did not form; this intermediate could only be observed when a deacylation deficient E166A variant was studied. We subsequently studied SA2-13 against a relatively recently discovered inhibitor-resistant (IR) variant of SHV-1, SHV K234R. Despite the alteration in the mechanism of resistance due to the K→R change in this variant, SA2-13 was effective at inhibiting this IR enzyme and formed a trans-enamine inhibitory intermediate similar to the intermediate seen in the wt SHV-1 structure. Taken together, our data reveals that the C2 side chain linker length and composition profoundly affect the formation of the trans-enamine intermediate of penam sulfones. We also show that the design of SA2-13 derivatives offers promise against IR SHV β-lactamases that possess the K234R substitution.

Design and exploration of novel boronic acid inhibitors reveals important interactions with a clavulanic acid-resistant sulfhydryl-variable (SHV) β-lactamase

Inhibitor resistant (IR) class A β-lactamases pose a significant threat to many current antibiotic combinations. The K234R substitution in the SHV β-lactamase, from Klebsiella pneumoniae , results in resistance to ampicillin/clavulanate. After site-saturation mutagenesis of Lys-234 in SHV, microbiological and biochemical characterization of the resulting β-lactamases revealed that only -Arg conferred resistance to ampicillin/clavulanate. X-ray crystallography revealed two conformations of Arg-234 and Ser-130 in SHV K234R. The movement of Ser-130 is the principal cause of the observed clavulanate resistance. A panel of boronic acid inhibitors was designed and tested against SHV-1 and SHV K234R. A chiral ampicillin analogue was discovered to have a 2.4 ± 0.2 nM K(i) for SHV K234R; the chiral ampicillin analogue formed a more complex hydrogen-bonding network in SHV K234R vs SHV-1. Consideration of the spatial position of Ser-130 and Lys-234 and this hydrogen-bonding network will be important in the design of novel antibiotics targeting IR β-lactamases.

Exploring the role of a conserved class A residue in the Ω-Loop of KPC-2 β-lactamase: a mechanism for ceftazidime hydrolysis

Gram-negative bacteria harboring KPC-2, a class A β-lactamase, are resistant to all β-lactam antibiotics and pose a major public health threat. Arg-164 is a conserved residue in all class A β-lactamases and is located in the solvent-exposed Ω-loop of KPC-2. To probe the role of this amino acid in KPC-2, we performed site-saturation mutagenesis. When compared with wild type, 11 of 19 variants at position Arg-164 in KPC-2 conferred increased resistance to the oxyimino-cephalosporin, ceftazidime (minimum inhibitory concentration; 32→128 mg/liter) when expressed in Escherichia coli. Using the R164S variant of KPC-2 as a representative β-lactamase for more detailed analysis, we observed only a modest 25% increase in k(cat)/K(m) for ceftazidime (0.015→0.019 μm(-1) s(-1)). Employing pre-steady-state kinetics and mass spectrometry, we determined that acylation is rate-limiting for ceftazidime hydrolysis by KPC-2, whereas deacylation is rate-limiting in the R164S variant, leading to accumulation of acyl-enzyme at steady-state. CD spectroscopy revealed that a conformational change occurred in the turnover of ceftazidime by KPC-2, but not the R164S variant, providing evidence for a different form of the enzyme at steady state. Molecular models constructed to explain these findings suggest that ceftazidime adopts a unique conformation, despite preservation of Ω-loop structure. We propose that the R164S substitution in KPC-2 enhances ceftazidime resistance by proceeding through "covalent trapping" of the substrate by a deacylation impaired enzyme with a lower K(m). Future antibiotic design must consider the distinctive behavior of the Ω-loop of KPC-2.

Induction of three histochemically distinct populations of hepatic foci in C57BL/6J mice

Although expression of the enzyme gamma-glutamyl transpeptidase (GGT) is the most common phenotypic marker of preneoplastic foci in the livers of carcinogen-treated rats, it is not generally expressed in mouse liver tumors or hepatic foci. However, several carcinogens, including safrole and ortho-azoaminotoluene (OAT), have been reported to induce GGT-positive foci in mice. We asked whether safrole and OAT induce GGT expression in preneoplastic foci or if these compounds select for a distinct set of lesions that can be identified by their GGT-positive phenotype. We treated 12-day-old male and female C57BL/6J mice with N,N-diethylnitrosamine (DEN) (0.20 mumol/g body wt) to initiate hepatocarcinogenesis. From 6 to 24 weeks of age, during the promotion phase of hepatocarcinogenesis, groups of mice were treated with 3,4,5,3',4',5'-hexabromobiphenyl (HBB), safrole or OAT. Additional groups of female mice were ovariectomized at 6 weeks of age with or without subsequent chronic treatment with testosterone. All the animals were killed at 24 weeks of age and serial liver sections were stained for glucose-6-phosphatase (G6Pase) or GGT. Both testosterone and HBB were strong promoters of the development of G6Pase-deficient foci. No GGT-positive foci were observed in animals treated with these agents or with DEN alone. In mice fed safrole or OAT during the promotion period, female mice developed more G6Pase-deficient foci than male mice, and GGT-positive foci were observed. Analysis of serial sections revealed that the G6Pase-deficient foci and the GGT-positive foci were independent populations. The relative number of these two classes of foci varied according to the treatment regimen. In females fed safrole, 7% of the foci in the liver were GGT-positive while in female mice fed OAT, 45% were GGT-positive. In all groups of mice in which we observed GGT-positive foci and in ovariectomized female mice, we noted a third independent population of foci which demonstrated significantly increased expression of G6Pase relative to surrounding normal liver. These data indicate that different treatments during the promotion stage of hepatocarcinogenesis in the mouse may give rise to distinct populations of preneoplastic lesions. Further studies of the molecular events giving rise to these distinct lesions will provide insights into the multiple pathways that result in hepatocarcinogenesis.

Partial hepatectomy is a promoter of hepatocarcinogenesis in C57BL/6J male mice but not in C3H/HeJ male mice

We have shown previously that the difference between C57BL/6J and C3H/HeJ male mice in their susceptibilities to chemically-induced liver tumors results predominantly from an allelic difference at the Hepatocarcinogen sensitivity (Hcs) locus. This locus modulates the rate of growth of preneoplastic liver lesions and may also play a role in the turnover of normal hepatocytes in the adult liver. To define further the growth regulatory pathway of which the Hcs gene is a component, we asked whether the expression of the Hcs gene would modulate the response of preneoplastic liver lesions to the physiologic growth stimulus generated by a two-thirds hepatectomy. Twelve-day-old male and female C57BL/6J and C3H/HeJ mice were injected with 0.5 mumols N-ethyl-N-nitrosourea/g body weight. At six weeks of age half the animals received a two-thirds hepatectomy. Groups of animals were killed between 14 and 44 weeks of age for analysis of glucose-6-phosphatase (G6Pase)-deficient foci and hepatic tumors. The partial hepatectomy induced a regenerative response that caused both the G6Pase-deficient foci and the surrounding, histochemically normal hepatocytes to undergo several rapid rounds of division. As a result, the G6Pase-deficient foci were larger in the hepatectomized animals than in the sham operated controls. The foci in the non-hepatectomized C57BL/6J male mice grew more slowly than in the C3H/HeJ male mice [volume doubling time (Td) = 2.9 +/- 0.1 weeks and 2.0 +/- 0.6 weeks, respectively]. Following partial hepatectomy, the G6Pase-deficient foci in the C57BL/6J male mice maintained a significantly higher growth rate (Td = 2.2 +/- 0.3 weeks) than the foci in the sham operated C57BL/6J male mice. The partial hepatectomy did not have any long term effect on the growth rate of the G6Pase-deficient foci in the C3H/HeJ male mice nor in female mice of either strain. At 32 weeks of age, the mean liver tumor multiplicity for hepatectomized C57BL/6J male mice was approximately 5.3-fold greater than that for sham operated animals. In contrast, a two-thirds hepatectomy resulted in a 60% reduction in the number of liver tumors in C3H/HeJ male mice relative to sham operated mice. These data demonstrate that partial hepatectomy can act as a promoter of hepatocarcinogenesis in C57BL/6J male mice but not C3H/HeJ male mice. We propose that the Hcs gene and partial hepatectomy may promote hepatocarcinogenesis through the same pathway of growth regulation.

Hepatic neoplasia: breath-hold MR imaging

Twenty-seven patients with hepatic neoplasms were prospectively examined at 0.35 T with multisection magnetic resonance (MR) imaging during a single breath hold. The procedures included a spin-echo (SE) sequence with a repetition time (TR) of 250 or 125 msec and an echo time (TE) of 15 msec (TR/TE = 250 or 125/15) and gradient-echo (GRE) partial-flip sequences at 250 or 125/20 in phase and 250 or 125/12 out of phase (flip angle of 70 degrees). These procedures were compared with conventional multiacquisition sequences at SE 250/15 (n = 8) in the same patients. GRE partial-flip sequences with a large flip angle provided the optimum combination of contrast and signal-to-noise ratio for imaging hepatic neoplasms, with a signal-difference-to-noise ratio that for in-phase images was 93% greater and for out-of-phase images was 53% greater than that of the SE images. The use of in-phase TEs was preferable to maintain tissue contrast, and presaturation pulses were employed to eliminate vascular pulsation artifacts. All breath-hold procedures provided suppression of motion artifacts superior to that of the short TR, short TE multiacquisition SE imaging. Such sequences should become indispensable for MR imaging of the upper abdomen.

Preservation of sickle cell blood-flow patterns during MR imaging: an in vivo study

Magnetic fields and RF energy have been shown to affect sickle erythrocytes in vitro. Because both strong magnetic fields and RF energy are used in MR imaging, it has been suggested that capillary blood flow in patients with sickle cell disease may be altered during MR imaging. In order to examine sickle cell blood flow during MR imaging in vivo, laser-Doppler velocimetry was performed in normal control subjects and in sickle cell subjects before, during, and after MR imaging at 0.35 and 1.5 T. Mean blood flow and patterns of blood-flow variability were compared by two hematologists. No differences were found on the recordings from each subject made before, during, and after MR imaging were compared. Blood-flow patterns generally differed between control and sickle cell subjects. Periodic oscillatory blood flow, reportedly a specific finding in sickle cell subjects, was observed in one control subject and was not consistently found in sickle cell subjects. Although energies employed during MR imaging have effects on sickle erythrocytes in vitro, our data show no changes in sickle cell blood flow during MR imaging in vivo.

Invasive cervical carcinoma: comparison of MR imaging and surgical findings

The accuracy of magnetic resonance (MR) imaging in staging invasive carcinoma of the cervix was determined retrospectively in 57 consecutive patients in whom the extent of disease was surgically confirmed. MR images were analyzed for (a) location and size of the primary tumor; (b) tumor extension to the uterine corpus, vagina, parametria, pelvic sidewall, bladder, or rectum; and (c) pelvic lymphadenopathy. The accuracy of MR imaging in determination of tumor location was 91% and for determination of tumor size within 0.5 cm, 70%. Its accuracy was 93% for vaginal extension and 88% for parametrial extension. Pelvic sidewall, bladder, and rectal involvement were accurately excluded in all patients, but the positive predictive values were 75%, 67%, and 100%, respectively. Overall, the accuracy of MR imaging in staging was 81%. MR imaging is valuable because it can accurately demonstrate tumor location, tumor size, degree of stromal penetration, and lower uterine segment involvement. It is also valuable for ruling out parametrial, pelvic sidewall, bladder, and rectal involvement.

Hemorrhagic and nonhemorrhagic brain lesions: evaluation with 0.35-T fast MR imaging

Two fast magnetic resonance (MR) imaging techniques, advanced Fourier and partial-flip imaging, were used at 0.35 T to examine 21 patients with suspected intracranial lesions; the results were quantitatively compared with a conventional spin-echo study. Both of the fast MR techniques yielded a fourfold reduction in imaging time per section. The advanced Fourier sequence showed contrast that was identical to the conventional spin-echo study with signal-to-noise ratios of 58% and 57% for the first and second echoes, respectively. The partial-flip sequence showed a contrast of 109% and 57% for lesions versus substantia alba, and 107% and 78% for substantia grisea versus substantia alba relative to the first and second echoes of the conventional spin-echo study. The partial-flip sequence was particularly sensitive to magnetic susceptibility; this produced artifacts that may undermine the usefulness of partial flip for routine screening in certain parts of the brain. However, this susceptibility significantly improved the detection of intracranial hemorrhage when compared with the spin-echo sequence, particularly when combined with phase mapping of the partial-flip study.

Undescended testis: value of MR imaging

Magnetic resonance (MR) imaging was performed in 32 male patients, 20 with no abnormalities and 12 with clinically suspected undescended testes. The results were compared with ultrasonographic, computed tomographic, clinical, and surgical findings. The undescended testes were unilateral in eight patients (one had testicular duplication) and bilateral in four. Of 16 undescended testes, 15 were correctly identified on MR images. One intraabdominal testis was not seen. Testis-fat contrast at 0.35 T was optimal with a short repetition time (TR) and a short echo time (TE). At 1.5 T, good contrast was achieved with short TR/TE sequences, but the contrast was even more pronounced with even longer TR/TE parameters. In seven patients with unilateral undescended testes, the undescended and contralateral testes showed symmetrical tissue signal intensity on both T1- and T2-weighted images. In three, the undescended testis was of lower signal intensity, suggesting atrophy. MR imaging promises to become an important diagnostic tool in the detection of undescended testes.

MR imaging of pulmonary arterial hypertension and pulmonary emboli

Intraluminal signal in the pulmonary arteries on spin-echo, ECG-gated MR images is limited to the diastolic phase of the cardiac cycle in normal subjects. Initial experience has indicated that signal persisting during systole may be characteristic of slow blood flow associated with pulmonary arterial hypertension (PAH) or of thrombotic material secondary to pulmonary embolism. This study analyzes our cumulative experience (31 patients) with multiphasic, double spin-echo MR for assessing PAH and/or suspected pulmonary embolism. In PAH, the abnormal systolic signal showed an intensity increase from first to second echo. This pattern was observed in 92% of PAH patients, including 100% of patients with pulmonary systolic pressures greater than or equal to 80 mm Hg and 60% of patients with pressures less than 80 mm Hg. At any focus in the pulmonary arteries, such signal disappeared at some phase of the cardiac cycle. In patients with pulmonary embolism, signal from thrombus was fixed throughout the cardiac cycle and showed little or no increase in relative intensity change from first- to second-echo image. Using this guideline, MR made six confirmed positive and four confirmed negative diagnoses of proximal pulmonary embolism, while it failed to identify thrombus in the one patient with a peripheral pulmonary embolism. Intraluminal signal in the pulmonary arteries caused by PAH or pulmonary embolism can be differentiated in most instances using multiphasic, double spin-echo, ECG-gated MR. However, at its current stage of development, the procedure does not appear to be useful for the evaluation of peripheral pulmonary embolism.

Adenomyosis and leiomyoma: differential diagnosis with MR imaging

To assess the capability of magnetic resonance (MR) imaging to enable differentiation of adenomyosis from leiomyoma, a prospective study was performed in 21 premenopausal patients with a strong clinical suggestion of adenomyosis. Histologic findings from hysterectomy (19 patients) and biopsy specimens (two patients) showed that eight patients had adenomyosis (three focal, five diffuse) and 12 had leiomyomas (five of the 12 also had microscopic foci of adenomyosis); one patient had a normal uterus. All eight cases of adenomyosis were correctly diagnosed from MR images. On T2-weighted MR images, diffuse adenomyosis appeared as a thickening of the junctional zone, whereas focal adenomyosis appeared as a low-signal-intensity mass poorly marginated from the adjacent myometrium. Ten of the 12 leiomyomas were correctly diagnosed from MR images. In the other two cases of leiomyoma, differentiation between focal adenomyosis and leiomyoma was not possible. Microscopic foci of adenomyosis were not demonstrated with MR imaging.

MR imaging in the diagnosis of pancreatic disease

MR imaging examinations of 20 patients with normal pancreas and of 38 patients with suspected pancreatic disease were analyzed retrospectively to evaluate the ability of MR imaging to depict the normal and abnormal pancreas, establish MR criteria for various pancreatic diseases, determine if MR imaging can distinguish among various pancreatic diseases, and compare the usefulness of MR imaging with CT. In all 20 patients with normal pancreas and in 34 of the 38 patients with suspected pancreatic disease excellent or good evaluation of the pancreas was achieved. A 0.35-T magnet (Diasonics MT/S) was used, and both T1- and T2-weighted images were needed. T1 and T2 relaxation times and MR signal intensities showed no specific pattern to allow consistent differentiation between normal and diseased pancreatic tissue or to distinguish between tumor and inflammation. In the 29 patients in whom MR and CT images could be compared, MR imaging and CT provided equivalent information in 20 (69%). In 4 patients (14%), MR imaging added information, and in 5 patients (17%) of cases, MR imaging yielded less information than CT. MR imaging of the pancreas was found to be superior to CT in selected instances, such as in the staging of pancreatic neoplasms (n = 4) and in the evaluation of pancreatic disease after surgery (n = 3). We conclude that, at present, MR imaging should not be used as the screening method for pancreatic disease but should be reserved as an adjunct when the information provided by CT is insufficient.

MR imaging of diffusely infiltrating gastric carcinoma

Magnetic resonance imaging of a diffusely infiltrating gastric carcinoma showed a markedly thickened gastric wall with low signal intensity on T1 and T2 weighted images. The T2 relaxation of the thickened gastric wall was very short, which was consistent with the histologically proven fibrous nature of the lesion.

Endometrial carcinoma staging by MR imaging

The potential of magnetic resonance (MR) imaging in the detection of endometrial carcinoma and in the assessment of its extent was evaluated prospectively in 51 patients clinically suspected of having the disease. MR imaging findings were compared with the results of surgical-pathologic staging and lymph node sampling following hysterectomy. Histologic findings showed 45 patients to have endometrial carcinoma, three to have no residual tumor after dilatation and curettage, and three to have adenomatous hyperplasia of the endometrium. MR imaging demonstrated an endometrial abnormality in 43 of the 51 patients (84%). Endometrial carcinoma could not be differentiated from adenomatous hyperplasia or blood clots. Therefore, MR imaging was not specific for tumor detection, and histologic diagnosis remains essential. The overall accuracy of MR imaging in staging endometrial carcinoma was 92%; its overall accuracy in demonstrating the depth of myometrial invasion was 82%. Demonstration of lymphadenopathy and adnexal or peritoneal metastases by MR imaging was suboptimal.

Gated acquisition of MR images of the thorax: advantages for the study of the hila and mediastinum

Gated and nongated magnetic resonance (MR) scans of the chest were compared in five normal volunteers and 20 patients with chest disease to determine possible advantages of gated MR for delineation of noncardiac mediastinal anatomy. In order to compare gated and nongated images of the chest using similar imaging parameters, five spin-echo sequences were obtained in each of five normal volunteers: TR: 1000 msec, TE: 30 msec; gated to every heart beat (TR approximately 1000 msec, TE: 30 msec); TR: 2000 msec, TE: 30 msec; gated to every other heart beat (TR approximately 2000 msec), TE: 30 msec; TR: 500 msec, TE: 30 msec. In the 20 patients, the gated images were gated to every heart beat and the nongated images were obtained using a TR of 2000 msec, both with a TE of 30 msec. The noise in the periphery and in the center of the gated and nongated images at the level of the carina was compared in the five normal volunteers, using the signal intensity of the posterior chest wall as a control. There was 92% +/- 44% greater noise in the central region and 63% +/- 60% greater noise in the peripheral region on the nongated studies (TR: 1000 msec), than on the studies gated to every heart beat. In three of the five volunteers, the measured noise was greater on the nongated long TR (2000 msec) images than on the images gated to every other heart beat. However, the mediastinal structures below the level of the aortic arch were much better defined on the gated images in all five subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Gestational trophoblastic neoplasm of the uterus: MR assessment

Magnetic resonance (MR) imaging characteristics of uterine gestational trophoblastic neoplasia were prospectively studied in nine women (aged 21-58 years). MR imaging was done at the time of initial clinical diagnosis, after each of the first two cycles of chemotherapy, and 6-9 months after initiation of chemotherapy. Sagittal and transverse MR images of the pelvis were generated with a 0.35-T superconducting magnet and the double spin-echo technique with short and long repetition times (TRs). The neoplasm distorted the MR appearance of uterine zonal structures (myometrium, endometrium, and junctional zone) and demonstrated hypervascular masses of heterogeneous signal intensity. Favorable response to chemotherapy was determined by a decrease in serum beta-subunit human chorionic gonadotropin (HCG) concentrations, and was accompanied by MR findings of regression of vascular abnormalities, development of intralesional hemorrhage, and return of normal appearance of uterine zones. The return of uterine zonal anatomy on MR images antedated definitive decrease in uterine volume. All eight patients imaged 6-9 months after initial imaging showed normal uterine volume and zonal anatomy.

MRI of perivalvular infectious pseudoaneurysms

MRI demonstrated perivalvular infectious pseudoaneurysms in three patients who had infective endocarditis that complicated cardiac surgery. In each case the infectious pseudoaneurysm, or abscess cavity, demonstrated absence of MR signal, consistent with the free flow of blood between it and the vessel lumen. Cardiac-gated MR images showed the precise location of the three infectious pseudoaneurysms in relation to the cardiac chambers: One was between the aortic root and left atrium; another was in the outflow portion of the ventricular septum; and the third surrounded the Rastelli conduit. Noninvasiveness, independence from the need for IV contrast material, precision in determining the site of the infectious pseudoaneurysm, and the lack of image artifacts produced by prosthetic valves make MRI a useful technique for detecting infectious cardiac pseudoaneurysms.

Pelvis imaging with MR: technique for improvement

Bowel peristalsis degrades magnetic resonance images of the pelvis. This degradation can be minimized by bowel preparation or by intramuscular administration of glucagon.

Cholecystitis: detection with MR imaging

The role of magnetic resonance (MR) imaging in the detection of gallbladder disease was evaluated in 39 individuals (16 healthy, five with asymptomatic gallstones, and 18 with clinical symptoms of gallbladder disease). MR imaging was performed after they fasted for 12 hours. Imaging sequences included a combination of repetition times (TR) of 0.5 and 1.5 sec and echo times (TE) of 28 and 56 msec. On the images obtained at TR = 0.5 sec and TE = 56 msec, gallbladder bile was hyperintense compared with the liver in all healthy and asymptomatic subjects and was hypointense (n = 9), isointense (n = 4), or hyperintense (n = 5) in symptomatic patients, eight of whom had surgical confirmation of cholecystitis. Comparison of normal versus pathologically proved cases for the presence of gallbladder disease yielded a specificity of 100%, sensitivity of 75%, and a significant difference of P less than .01. Thus, with a pulse sequence of TR = 0.5 sec and TE = 56 msec, MR was sensitive in detecting gallbladder disease. However, the role of MR in the radiologic workup of gallbladder disease will be determined by more experience with this modality.

Electron microscopic demonstration of lysosomal inclusion bodies in lung, liver, lymph nodes, and blood leukocytes of patients with amiodarone pulmonary toxicity

The mechanism of amiodarone-induced pulmonary toxicity is unknown. Two cases of amiodarone pulmonary toxicity are presented in which abnormal inclusion bodies containing whorls of membrane were seen on electron microscopy of extrapulmonary tissues. These cytoplasmic lysosomal inclusion bodies were observed in lymphocytes, plasma cells, granulocytes, tissue macrophages, and hepatocytes. These widespread histopathologic changes in extrapulmonary tissues and in a variety of cell types are similar to more extensively investigated findings in animal models that are thought to represent a drug-induced lysosomal storage disease, phospholipidosis.

Increased hepatic density and phospholipidosis due to amiodarone

Amiodarone is an amphiphilic iodinated compound that is used as a treatment for refractory ventricular arrhythmias. During evaluation for possible pulmonary toxicity, a patient receiving amiodarone was noted to have an increase in the density of his liver as seen on computed tomographic (CT) scanning of the abdomen. Six additional patients who were receiving amiodarone were subsequently evaluated to ascertain the frequency of this finding. The CT density of the liver was increased in all patients. Values obtained varied from 95 to 145 H, with a mean of 117 +/- 8.9 (normal, 30-70). The alkaline phosphatase was elevated in four patients, but only one had an elevation of either the alanine or aspartate aminotransferase. Two patients underwent liver biopsies, and both revealed membranous lamellar phospholipid-containing structures within hepatocytes. Animal studies done to recreate these findings revealed that amiodarone accumulated in the liver at concentrations 175-500 times greater than those found in serum. Quantitative measurements of iodine in samples from the same liver showed that the iodine levels were correspondingly elevated. In the treated animals, there was a small but statistically significant increase in the CT density of the liver, whereas the values for untreated animals were unchanged. Treatment with amiodarone leads to an accumulation in the liver of this iodinated compound and hence an increase in the CT density of the liver. This accumulation of the drug in hepatic lysosomes apparently causes a secondary phospholipidosis.

Hemodynamic correlates of right ventricular ejection fraction measured with gated radionuclide angiography

Right ventricular function was studied in 60 patients with equilibrium gated radionuclide angiography. The mean (+/- standard deviation) right ventricular ejection fraction in 20 normal subjects was 53 +/- 6 percent, a value in agreement with previous data from both radionuclide and contrast angiographic studies. This value was similar (55 +/- 7 percent) in 11 patients with coronary artery disease but normal left ventricular function. Radionuclide measurements of right ventricular ejection fraction were correlated with right heart hemodynamics. There was a significant negative linear correlation between right ventricular ejection fraction and mean pulmonary arterial pressure (r = -0.82) and between right ventricular ejection fraction and right ventricular end-diastolic pressure (4 = -0.67). Furthermore, patients with elevated right ventricular end-diastolic pressure and mean pulmonary arterial pressure had a more severely depressed ejection fraction than did those with an elevated mean pulmonary arterial pressure alone. Thus, an abnormal value for right ventricular ejection fraction by gated radionuclide angiography in the absence of primary right ventricular volume overload suggests abnormal right heart pressures, whereas a normal value excludes severe pulmonary arterial hypertension or an elevated right ventricular end-diastolic pressure.