Influence of ceftriaxone treatment on FDG uptake--an in vivo [18F]-fluorodeoxyglucose imaging study in soft tissue infections in rats

CodY is modulated by YycF and affects biofilm formation in Staphylococcus aureus

Background

Staphylococcus aureus (S. aureus) is the leading cause of various infective diseases, including topical soft tissue infections. The goals of this study were to investigate the roles of YycF and CodY in the regulation of biofilm formation and pathogenicity.

Methods

Electrophoretic mobility shift assay (EMSA) was conducted to validate the bound promoter regions of YycF protein. We constructed the codY up-regulated or down-regulated S. aureus mutants. The biofilm biomass was determined by crystal violet microtiter assay and scanning electron microscopy (SEM). Quantitative RT-PCR analysis was used to detect the transcripts of biofilm-related genes. The live and dead cells of S. aureus biofilm were also investigated by confocal laser scanning microscopy (CLSM). We constructed an abscess infection in Sprague Dawley (SD) rat models to determine the effect of CodY on bacterial pathogenicity. We further used the RAW264.7, which were cocultured with S. aureus, to evaluate the effect of CodY on macrophages apoptosis.

Result

Quantitative RT-PCR analyses reveled that YycF negatively regulates codY expression. EMSA assays indicated that YycF protein directly binds to the promoter regions of codY gene. Quantitative RT-PCR confirmed the construction of dual- mutant stains codY + ASyycF and codY-ASyycF. The SEM results showed that the biofilm formation in the codY + ASyycF group was sparser than those in the other groups. The crystal violet assays indicated that the codY + ASyycF group formed less biofilms, which was consistent with the immunofluorescence results of the lowest live cell ration in the codY + ASyycF group. The expression levels of biofilm-associated icaA gene were significantly reduced in the codY + strain, indicating codY negatively regulates the biofilm formation. Furthermore, CodY impedes the pathogenicity in a rat-infection model. After cocultured with bacteria or 4-h in vitro, the apoptosis rates of macrophage cells were lowest in the codY + group.

Conclusions

YycF negatively regulate the expression of codY. By interaction with codY, YycF could modulate S. aureus biofilm formation via both eDNA- dependent and PIA- dependent pathways, which can be a significant target for antibiofilm. CodY not only impedes the pathogenicity but also has a role on immunoregulation. Thus, the current evidence may provide a supplementary strategy for managing biofilm infections.

Imaging Enterobacteriaceae infection in vivo with 18F-fluorodeoxysorbitol positron emission tomography

The Enterobacteriaceae are a family of rod-shaped Gram-negative bacteria that normally inhabit the gastrointestinal tract and are the most common cause of Gram-negative bacterial infections in humans. In addition to causing serious multidrug-resistant, hospital-acquired infections, a number of Enterobacteriaceae species are also recognized as biothreat pathogens. As a consequence, new tools are urgently needed to specifically identify and localize infections due to Enterobacteriaceae and to monitor antimicrobial efficacy. In this report, we used commercially available 2-[(18)F]-fluorodeoxyglucose ((18)F-FDG) to produce 2-[(18)F]-fluorodeoxysorbitol ((18)F-FDS), a radioactive probe for Enterobacteriaceae, in 30 min. (18)F-FDS selectively accumulated in Enterobacteriaceae, but not in Gram-positive bacteria or healthy mammalian or cancer cells in vitro. In a murine myositis model, (18)F-FDS positron emission tomography (PET) rapidly differentiated true infection from sterile inflammation with a limit of detection of 6.2 ± 0.2 log10 colony-forming units (CFU) for Escherichia coli. Our findings were extended to models of mixed Gram-positive and Gram-negative thigh co-infections, brain infection, Klebsiella pneumonia, and mice undergoing immunosuppressive chemotherapy. This technique rapidly and specifically localized infections due to Enterobacteriaceae, providing a three-dimensional holistic view within the animal. Last, (18)F-FDS PET monitored the efficacy of antimicrobial treatment, demonstrating a PET signal proportionate to the bacterial burden. Therapeutic failures associated with multidrug-resistant, extended-spectrum β-lactamase (ESBL)-producing E. coli infections were detected in real time. Together, these data show that (18)F-FDS is a candidate imaging probe for translation to human clinical cases of known or suspected infections owing to Enterobacteriaceae.

PET/CT imaging in infectious conditions

New aggressive pathogens are responsible for the increasing incidence and difficult management of infections. Modern epidemics such as diabetes are frequently complicated by severe infections with subsequent high morbidity. Diagnosis (essentially early detection of infection) and also management decision making pose clinical challenges. Many resources are invested in developing precise, noninvasive diagnostic tests and efficient therapies for infectious processes. Nuclear medicine procedures are part of the evaluation armamentarium of patients with suspected or confirmed infection. Their strength relies on the fact that they are noninvasive tests that provide both functional as well as metabolic information early in the course of disease. Their limitations relate to the need for specific radiotracers and the rather low resolution of images. These limitations have been largely overcome by the hybrid PET/CT and SPECT/CT technology. PET/CT, primarily using FDG, is redefining the diagnostic work up and is currently leading to changes in the management of patients with suspected or known infections. The main indications for FDG PET/CT in infection, as well as updated literature results, are presented in the following review.

Combined PET and X-ray computed tomography imaging in pulmonary infections and inflammation

PURPOSE OF REVIEW

This review addresses issues relating to the use of the relatively new combined PET and X-ray computed tomography (PET/CT) modality for imaging pulmonary infections and inflammation, as well as assessing its potential for this purpose.

RECENT FINDINGS

Accurate definition and monitoring of the extent of lung infection is difficult using conventional chest radiograph, CT scan, MRI, and radioisotope scintigraphy. In the last decade, PET/CT using radiolabeled fluorodeoxyglucose has been added to the imaging armamentarium, mostly for imaging lung cancer. To date, very few data are available on the application of this technique for imaging pulmonary infections and inflammation; however, this situation is changing, and there is now more interest in using PET/CT for this purpose. In addition, there are new tracers on the horizon which remain to be exploited.

SUMMARY

This review addresses some of these issues and outlines the potential to use PET/CT for noncancer pulmonary indications.

The additional value of CT images interpretation in the differential diagnosis of benign vs. malignant primary bone lesions with 18F-FDG-PET/CT

OBJECTIVE

To evaluate the value of a dedicated interpretation of the CT images in the differential diagnosis of benign vs. malignant primary bone lesions with 18 fluorodeoxyglucose-positron emission tomography/computed tomography (18F-FDG-PET/CT).

MATERIALS AND METHODS

In 50 consecutive patients (21 women, 29 men, mean age 36.9, age range 11-72) with suspected primary bone neoplasm conventional radiographs and 18F-FDG-PET/CT were performed. Differentiation of benign and malignant lesions was separately performed on conventional radiographs, PET alone (PET), and PET/CT with specific evaluation of the CT part. Histology served as the standard of reference in 46 cases, clinical, and imaging follow-up in four cases.

RESULTS

According to the standard of reference, conventional 17 lesions were benign and 33 malignant. Sensitivity, specificity, and accuracy in assessment of malignancy was 85%, 65% and 78% for conventional radiographs, 85%, 35% and 68% for PET alone and 91%, 77% and 86% for combined PET/CT. Median SUV(max) was 3.5 for benign lesions (range 1.6-8.0) and 5.7 (range 0.8-41.7) for malignant lesions. In eight patients with bone lesions with high FDG-uptake (SUV(max) >or= 2.5) dedicated CT interpretation led to the correct diagnosis of a benign lesion (three fibrous dysplasias, two osteomyelitis, one aneurysmatic bone cyst, one fibrous cortical defect, 1 phosphaturic mesenchymal tumor). In four patients with lesions with low FDG-uptake (SUV(max) < 2.5) dedicated CT interpretation led to the correct diagnosis of a malignant lesion (three chondrosarcomas and one leiomyosarcoma). Combined PET/CT was significantly more accurate in the differentiation of benign and malignant lesions than PET alone (p = .039). There was no significant difference between PET/CT and conventional radiographs (p = .625).

CONCLUSION

Dedicated interpretation of the CT part significantly improved the performance of FDG-PET/CT in differentiation of benign and malignant primary bone lesions compared to PET alone. PET/CT more commonly differentiated benign from malignant primary bone lesions compared with conventional radiographs, but this difference was not significant.

Role of modern imaging techniques for diagnosis of infection in the era of 18F-fluorodeoxyglucose positron emission tomography

During the past several years, it has become quite evident that positron emission tomography (PET) with 18F-fluorodeoxyglucose (FDG) imaging can play a major role in the management of patients with suspected infection. Particularly, several groups have demonstrated that this powerful imaging methodology is very effective in the evaluation of osteomyelitis, infected prostheses, fever of unknown origin, and AIDS. In view of its extraordinary sensitivity in detecting disease activity and the ability to quantitate the degree of FDG uptake, PET might prove to be an appropriate modality for monitoring disease activity and evaluating response to therapy. FDG-PET has many advantages over existing imaging techniques for the diagnosis of infectious diseases. These include feasibility of securing diagnostic results within 1.5 to 2 h, excellent spatial resolution, and accurate anatomical localization of sites of abnormality. The availability of PET/computed tomography as a practical tool has further enhanced the role of metabolic imaging in many settings. In the future, this modality is very likely to be employed on a routine basis for detecting, characterizing, and monitoring patients with suspected and proven infection.

Improvement of semi-quantitative small-animal PET data with recovery coefficients: A phantom and rat study

AIM

To evaluate the accuracy of semi-quantitative small-animal PET data, uncorrected for attenuation, and then of the same semi-quantitative data corrected by means of recovery coefficients (RCs) based on phantom studies.

MATERIALS AND METHODS

A phantom containing six fillable spheres (diameter range: 4.4-14 mm) was filled with an 18F-FDG solution (spheres/background activity=10.1, 5.1 and 2.5). RCs, defined as measured activity/expected activity, were calculated. Nude rats harbouring tumours (n=50) were imaged after injection of 18F-FDG and sacrificed. The standardized uptake value (SUV) in tumours was determined with small-animal PET and compared to ex-vivo counting (ex-vivo SUV). Small-animal PET SUVs were corrected with RCs based on the greatest tumour diameter. Tumour proliferation was assessed with cyclin A immunostaining and correlated to the SUV.

RESULTS

RCs ranged from 0.33 for the smallest sphere to 0.72 for the largest. A sigmoidal correlation was found between RCs and sphere diameters (r(2)=0.99). Small-animal PET SUVs were well correlated with ex-vivo SUVs (y=0.48x-0.2; r(2)=0.71) and the use of RCs based on the greatest tumour diameter significantly improved regression (y=0.84x-0.81; r(2)=0.77), except for tumours with important necrosis. Similar results were obtained without sacrificing animals, by using PET images to estimate tumour dimensions. RC-based corrections improved correlation between small-animal PET SUVs and tumour proliferation (uncorrected data: Rho=0.79; corrected data: Rho=0.83).

CONCLUSION

Recovery correction significantly improves both accuracy of small-animal PET semi-quantitative data in rat studies and their correlation with tumour proliferation, except for largely necrotic tumours.

Radionuclide imaging of spinal infections

BACKGROUND

The diagnosis of spinal infection, with or without implants, has been a challenge for physicians for many years. Spinal infections are now being recognised more frequently, owing to aging of the population and the increasing use of spinal-fusion surgery.

DISCUSSION

The diagnosis in many cases is delayed, and this may result in permanent neurological damage or even death. Laboratory evidence of infection is variable. Conventional radiography and radionuclide bone imaging lack both sensitivity and specificity. Neither in vitro labelled leucocyte scintigraphy nor 99mTc-anti-granulocyte antibody scintigraphy is especially useful, because of the frequency with which spinal infection presents as a non-specific photopenic area on these tests. Sequential bone/gallium imaging and 67Ga-SPECT are currently the radionuclide procedures of choice for spinal osteomyelitis, but these tests lack specificity, suffer from poor spatial resolution and require several days to complete. [18F]Fluoro-2-deoxy-D-glucose (FDG) PET is a promising technique for diagnosing spinal infection, and has several potential advantages over conventional radionuclide tests.

RESULTS

The study is sensitive and is completed in a single session, and image quality is superior to that obtained with single-photon emitting tracers. The specificity of FDG-PET may also be superior to that of conventional tracers because degenerative bone disease and fractures usually do not produce intense FDG uptake; moreover, spinal implants do not affect FDG imaging. However, FDG-PET images have to be read with caution in patients with instrumented spinal-fusion surgery since non-specific accumulation of FDG around the fusion material is not uncommon.

CONCLUSION

In the future, PET-CT will likely provide more precise localisation of abnormalities. FDG-PET may prove to be useful for monitoring response to treatment in patients with spinal osteomyelitis. Other tracers for diagnosing spinal osteomyelitis are also under investigation, including radiolabelled antibiotics, such as 99mTc-ciprofloxacin, and radiolabelled streptavidin-biotin complex. Antimicrobial peptides display preferential binding to microorganisms over human cells and perhaps new radiopharmaceuticals will be recruited from the array of human antimicrobial peptides/proteins. In experiments with Tc-ubiquicidin-derived peptides, radioactivity at the site of infection correlated well with the number of viable bacteria present. Finally, radiolabelled antifungal tracers could potentially distinguish fungal from bacterial infections.

Biodistribution and Imaging of FDG in Rats with LS174T Carcinoma Xenografts and Focal Escherichia coli Infection

OBJECTIVE

The aim of this study was to compare the dynamic distribution of fluorodeoxyglucose (FDG) in malignant and in infectious lesions.

METHODS

The dynamic distribution of FDG was studied in Rowett nude (RNU) rats with a LS174T carcinoma xenograft in the left front leg and an Escherichia coli-induced focal infection in the right front leg. In 5 rats, dynamic FDG-PET was performed (27 frames of 6-15 minutes) up to 4 hours after injection of 11 MBq 18FDG. The mean FDG uptake (SUV) was calculated and plotted by using a region of interest (ROI) centered over both lesions. In groups of 6 rats, the biodistribution of FDG was determined by counting dissected tissues at 1, 2, 3, and 4 hours after an injection of 11 MBq FDG. Means +/- the standard error of the mean (SEM) were calculated.

RESULTS

Dynamic positron emission tomography (PET) visualized both the tumor and the infection. The ROI analysis showed that FDG uptake in the infections was faster and higher, as compared to the tumor lesions. FDG uptake in the tumor reached a standardized uptake value (SUV) of 0.8 +/- 0.3 at 60 minutes and in the infectious lesions a SUV of 1.6 +/- 0.2 at 45 minutes, both remaining constant until 4 hours postinjection (p.i.). In the biodistribution study with ex vivo tissue counting, FDG had accumulated up to 1.1 +/- 0.1 %ID/g and 0.8 +/- 0.1 %ID/g at 1 hour in the tumor and infection, respectively, and remained constant until 4 hours for both lesions without significantly different wash-out from the 2 lesions. The tumor/blood and abscess/ blood ratios increased with time to 57 +/- 17 and 48 +/- 14, respectively.

CONCLUSION

Although in this model differences in absolute FDG uptake and initial kinetics between tumor and infection were observed, the wash-out rate of FDG from the lesions was similar over time. The retention of FDG in the inflammatory lesion indicated that dual time-point imaging does not necessarily resolve diagnostic pitfalls for FDG-PET in oncology in order to discriminate between malignant tumorous and benign infectious lesions.