Imaging Inflammation and Infection in the Gastrointestinal Tract.

A variety of seemingly non-specific symptoms manifest within the gastrointestinal (GI) tract, particularly in the colon, in response to inflammation, infection, or a combination thereof. Differentiation between symptom sources can often be achieved using various radiologic studies. Although it is not possible to provide a comprehensive survey of imaging gastrointestinal GI tract infections in a single article, the purpose of this review is to survey several topics on imaging of GI tract inflammation and infections. The review discusses such modalities as computed tomography, positron emission tomography, ultrasound, endoscopy, and magnetic resonance imaging while looking at up-an-coming technologies that could improve diagnoses and patient comfort. The discussion is accomplished through examining a combination of organ-based and organism-based approaches, with accompanying selected case examples. Specific focus is placed on the bacterial infections caused by Shigella spp., Escherichia coli, Clostridium difficile, Salmonella, and inflammatory conditions of diverticulitis and irritable bowel disease. These infectious and inflammatory diseases and their detection via molecular imaging will be compared including the appropriate differential diagnostic considerations.

Imaging Ca2+ Responses During Shigella Infection of Epithelial Cells.

Ca2+ is a ubiquitous ion involved in all known cellular processes. While global Ca2+ responses may affect cell fate, local variations in free Ca2+ cytosolic concentrations, linked to release from internal stores or an influx through plasma membrane channels, regulate cortical cell processes. Pathogens that adhere to or invade host cells trigger a reorganization of the actin cytoskeleton underlying the host plasma membrane, which likely affects both global and local Ca2+ signaling. Because these events may occur at low frequencies in a pseudo-stochastic manner over extended kinetics, the analysis of Ca2+ signals induced by pathogens raises major technical challenges that need to be addressed. Here, we report protocols for the detection of global and local Ca2+ signals upon a Shigella infection of epithelial cells. In these protocols, artefacts linked to a prolonged exposure and photodamage associated with the excitation of Ca2+ fluorescent probes are troubleshot by stringently controlling the acquisition parameters over defined time periods during a Shigella invasion. Procedures are implemented to rigorously analyze the amplitude and frequency of global cytosolic Ca2+ signals during extended infection kinetics using the chemical probe Fluo-4.

Imaging macropinosomes during Shigella infections.

Macropinocytosis is the uptake of extracellular fluid within vesicles of varying size that takes place during numerous cellular processes in a large variety of cells. A growing number of pathogens, including viruses, parasites, and bacteria are known to induce macropinocytosis during their entry into targeted host cells. We have recently discovered that the human enteroinvasive, bacterial pathogen Shigella causes in situ macropinosome formation during its entry into epithelial cells. These infection-associated macropinosomes are not generated to ingest the bacteria, but are instead involved in Shigella's intracellular niche formation. They make contacts with the phagocytosed shigellae to promote vacuolar membrane rupture and their cytosolic release. Here, we provide an overview of the different imaging approaches that are currently used to analyze macropinocytosis during infectious processes with a focus on Shigella entry. We detail the advantages and disadvantages of genetically encoded reporters as well as chemical probes to trace fluid phase uptake. In addition, we report how such reporters can be combined with ultrastructural approaches for correlative light electron microscopy either in thin sections or within large volumes. The combined imaging techniques introduced here provide a detailed characterization of macropinosomes during bacterial entry, which, apart from Shigella, are relevant for numerous other ones, including Salmonella, Brucella or Mycobacteria.

Sonographic findings in Shigella colitis.

We present a case of colitis caused by Shigella sonnei in which abdominal sonography helped in the early diagnosis, leading to successful conservative management. Sonography showed diffuse wall thickening and layer stratification in the descending and sigmoid colon. Although Shigella colitis is relatively rare, the possibility must be considered when patients have diffuse wall thickening with distinct layer stratification in the left colon.

Salmonella- and Shigella-induced ileitis: CT findings in four patients.

PURPOSE: The purpose of this study is to describe and illustrate the CT appearance of four cases of acute terminal ileitis induced by nontyphoidal Salmonella and Shigella infection and to review the radiographic and endoscopic findings of these entities. METHOD: The medical records, CT examinations, and small bowel examinations of three patients with Salmonella ileitis and one patient with Shigella ileitis were retrospectively reviewed. CT examinations were done in four patients, colonoscopy in three patients, and small bowel examinations in two patients. Stool cultures established the diagnosis of nontyphoidal Salmonella enteritis in three patients and Shigella enteritis in one patient. The patients' symptoms and clinical findings resolved promptly following supportive therapy and appropriate antibiotic therapy. RESULTS: CT showed slight circumferential and homogeneous thickening of the terminal ileum over a segment of 10-15 cm in patients with Salmonella ileitis. Associated mild thickening of the wall of the colon was present in addition. Small bowel examination performed in one patient revealed a spastic terminal ileum with thickened mucosal folds. Colonoscopy revealed acute colitis involving the colon diffusely in one case, but sparing the distal 50 cm of the colon in one case. CT showed more pronounced thickening of the terminal ileum and a target configuration in the patient with Shigella ileitis. Small bowel examination revealed narrowing, irregular contour, several large nodular defects (thumbprinting), and a severely ulcerated mucosa affecting the terminal ileum. Colonoscopy revealed a normal colon and large ulcerations with fibropurulent exudate in the terminal ileum. CONCLUSION: In patients with severe Salmonella or Shigella infections or persistent and/or confusing clinical presentations, CT can play a complementary but important role in the initial diagnostic evaluation. It avoids clinical mismanagement, circumvents unnecessary invasive procedures, and contributes to the efficient workup and therapy in this group of individuals.