Role of EspB in experimental human enteropathogenic Escherichia coli infection.

Enteropathogenic Escherichia coli (EPEC), a leading cause of diarrhea among infants in developing countries, induces dramatic alterations in host cell architecture that depend on a type III secretion system. EspB, one of the proteins secreted and translocated to the host cytoplasm via this system, is required for numerous alterations in host cell structure and function. To determine the role of EspB in virulence, we conducted a randomized, double-blind trial comparing the ability of wild-type EPEC and an isogenic DeltaespB mutant strain to cause diarrhea in adult volunteers. Diarrhea developed in 9 of 10 volunteers who ingested the wild-type strain but in only 1 of 10 volunteers who ingested the DeltaespB mutant strain. Marked destruction of the microvillous brush border adjacent to adherent organisms was observed in a jejunal biopsy from a volunteer who ingested the wild-type strain but not from two volunteers who ingested the DeltaespB mutant strain. Humoral and cell-mediated immune responses to EPEC antigens were stronger among recipients of the wild-type strain. In addition, four of the volunteers who ingested the wild-type strain had lymphoproliferative responses to EspB. These results demonstrate that EspB is a critical virulence determinant of EPEC infections and suggest that EspB contributes to an immune response.

Primary posttransplant lymphoproliferative disorder of the gallbladder in a lung transplant patient presenting with acute cholecystitis.

BACKGROUND: Acute cholecystitis in an immunocompromised host is potentially devastating. Posttransplant lymphoproliferative disorder (PTLD) is a well described complication of immunosuppressive therapy used after solid organ transplantation; however, isolated involvement of the gallbladder has not been described. METHODS: Case report format is used. RESULTS: We report a case of PTLD isolated to the gallbladder, as well as histological evidence of acute cholecystitis, in a patient who presented with signs and symptoms of acute cholecystitis 1 year after single lung transplant. CONCLUSIONS: PTLD can occur in the setting of acute cholecystitis and may be missed if careful pathological examination is not undertaken.

Validation of a gastrointestinal explant system for measurement of mucosal antibody production.

A gastrointestinal explant culture system was developed and compared to the mononuclear cell extraction and enzyme-linked immunospot assay method for measurement of immunoglobulin A (IgA) and IgG antibody-secreting cells (ASCs) in gastric antral and duodenal biopsies of non-Helicobacter pylori-infected volunteers. IgA and IgG were detected in explant supernatants during 6 to 7 days of culture in all subjects. IgA containing secretory component was also detected throughout the culture period, although peak production occurred only in the first 3 days. During 7 days of culture, the cumulative geometric mean IgA levels produced were 2.2 and 8.02 microg/ml/10 mg of antral and duodenal biopsy tissues, respectively, while the cumulative geometric mean IgG levels were 1.54 and 2.92 microg/ml/10 mg of antral and duodenal biopsy tissues, respectively. Cycloheximide treatment resulted in a >90% reduction in both immunoglobulin classes after 6 days of treatment compared to levels in untreated controls. The detection of IgA and IgG ASCs extracted from biopsies on days 1 and 6 of culture confirmed that the antibody detected was derived from mucosal lamina propria. The IgA and IgG ASC responses were positively correlated with antibody concentrations detected in culture supernatants (r = 0.87 and 0.85, respectively). These results validate the potential usefulness of our gastrointestinal explant system for the evaluation of mucosal effector B-cell function.

Increased expression and cellular localization of inducible nitric oxide synthase and cyclooxygenase 2 in Helicobacter pylori gastritis.

BACKGROUND & AIMS: Inducible nitric oxide synthase (iNOS) and cyclooxygenase (COX)-2 are important regulators of mucosal inflammation and epithelial cell growth. To determine the role of iNOS and COX-2 in Helicobacter pylori-induced tissue injury, we compared their gene expression in H. pylori-induced gastritis with that in normal gastric mucosa and in non-H. pylori gastritis. METHODS: In 43 patients, we assessed H. pylori infection status, histopathology, messenger RNA (mRNA) and protein expression, and cellular localization of iNOS and COX-2. RESULTS: By reverse-transcription polymerase chain reaction (RT-PCR), antral iNOS and COX-2 mRNA expression was absent to low in normal mucosa (n = 10), significantly increased in H. pylori-negative gastritis (n = 13), and even more markedly increased in H. pylori-positive gastritis (n = 20). Increased iNOS and COX-2 levels were confirmed by Northern and Western blot analysis and were both greater in the gastric antrum than in the gastric body of infected patients. Immunohistochemistry also showed increased expression of both genes in H. pylori gastritis: iNOS protein was detected in epithelium, endothelium, and lamina propria inflammatory cells, and COX-2 protein localized to mononuclear and fibroblast cells in the lamina propria. CONCLUSIONS: iNOS and COX-2 are induced in H. pylori-positive gastritis and thus may modulate the inflammation and alterations in epithelial cell growth that occur in this disease. Higher levels of iNOS and COX-2 in H. pylori-positive vs. -negative gastritis and in gastric antrum, where bacterial density is greatest, suggest that expression of these genes is a direct response to H. pylori infection.

Pathogenesis of Helicobacter pylori infection.

Intensive investigation into the interactions of Helicobacter pylori with the human host during the period of this review has led to several important developments in our understanding of H. pylori pathogenesis. There is direct evidence to support a central role for bacterial adhesion to host gastric epithelial Lewis antigens. Adherence can result in activation of host signaling cascades, including tyrosine phosphorylation events. H. pylori induces an immune response that is skewed toward a T-helper cell (Th) 1 phenotype, and an insufficient Th2 response is associated with the inability of the host to eradicate the organism. An area of active investigation has been the induction of epithelial apoptosis, both in direct response to H. pylori and by T-cell mediated pathways. Although the consensus is that the cagA gene product is not involved in pathogenesis, the presence of the cag pathogenicity island is associated with increased gastric inflammation and decreased epithelial repair. Interestingly, infection with cagA+H. pylori appears to result in decreased prevalence of both gastroesophageal reflux disease and adenocarcinoma of the esophagus and cardia.

Decreased prevalence of Helicobacter pylori infection in gastroesophageal reflux disease.

BACKGROUND: An increased incidence of reflux esophagitis has been reported after eradication of H. pylori in patients with duodenal ulcer. To determine if H. pylori is associated with lower rates of esophagitis, we studied the prevalence of H. pylori infection in patients with and without reflux esophagitis and a subgroup of patients with concomitant peptic ulcer disease. METHODS: Patients who underwent esophagogastroduodenoscopy and had diagnostic testing for H. pylori over a 30-month period were studied. H. pylori infection was determined by rapid urease testing, gastric histopathology, or serology. Reflux esophagitis was determined by endoscopic and/or histologic criteria. RESULTS: Of 514 patients, 39.5% had H. pylori infection and 22.2% had reflux esophagitis. The prevalence of H. pylori infection in patients with reflux esophagitis was 30.7%, compared with 42.0% in patients without esophagitis (p = 0.039). The odds ratio for esophagitis risk with H. pylori infection was 0.61 (95% CI, 0.39-0.95). Neither patient age nor gender affected H. pylori prevalence. In patients with duodenal ulcer, H. pylori was present in 36.4% of patients with esophagitis and in 69.2% of patients without esophagitis (p = 0.018). The odds ratio for esophagitis with H. pylori infection in these patients was 0.25 (95% CI, 0.09-0.73). CONCLUSIONS: Our study demonstrates that H. pylori infection is significantly less prevalent in patients with reflux esophagitis and may protect against its development. In duodenal ulcer patients, this effect was more dramatic. Further study is required to confirm these findings and elucidate mechanisms underlying possible beneficial effects of H. pylori.

Mixed infection with cagA-positive and cagA-negative strains of Helicobacter pylori.

BACKGROUND: Helicobacter pylori infection has been implicated strongly in the pathogenesis of gastritis, peptic ulcer disease, gastric adenocarcinoma, and gastric lymphoma, but the reasons for these widely different clinical outcomes are unknown. The aim of this study was to determine whether these differences could be due in part to mixed infection in the same individual, with bacteria having differences in pathogenic factors associated with ulcers. MATERIALS AND METHODS: The cagA gene of H. pylori was used to test for mixed infection because it is present in only some strains, and its presence has been associated with ulcers. Polymerase chain reaction (PCR) assays for the cagA gene were applied to H. pylori culture isolates and endoscopic gastric aspirates. Individual bacterial clones were tested for genetic similarity by random primer amplification and restriction endonuclease digestion of urease gene PCR products. RESULTS: The majority of H. pylori-positive patients had strongly cagA-positive culture isolates and endoscopic samples (62.5% and 69.6%, respectively). However, many of these patients had evidence of mixed infection with cagA negative and cagA positive strains in cultures isolates and endoscopic samples (25% and 17.4%, respectively). Mixed infection was found to be due to genetically unrelated strains in two patients in whom genetic analysis was performed. CONCLUSION: Mixed infection with differences in substrain pathogenic factors might occur in H. pylori infection and might contribute to differences in clinical outcome.

Immune evasion by Helicobacter pylori: gastric spiral bacteria lack surface immunoglobulin deposition and reactivity with homologous antibodies.

BACKGROUND: Helicobacter pylori infection persists in the presence of potent serum and gastric mucosal antibody responses against bacterial antigens. The aim of this article is to report on a study determine whether there is antibody deposition on H. pylori in vivo in the stomach of infected patients and whether gastric and cultured forms of H. pylori differ in their antibody reactivity. MATERIALS AND METHODS: Serum, gastric biopsies, and antral brushings were obtained from 10 patients having endoscopy. H. pylori was cultured from gastric biopsies. Bacterial samples were stained directly for immunoglobulin deposition and indirectly using rabbit antiurease serum or patient serum. Samples were examined by immunofluorescence microscopy and flow cytometry. RESULTS: Although spiral bacteria could be identified easily by acridine orange staining and antiurease staining of gastric brushings from H. pylori infected patients, gastric bacteria did not have detectable IgG or IgA present, and only one of five samples could be stained for IgG and IgA indirectly using patient serum. In contrast, cultured bacteria could be stained readily with homologous serum for IgG and IgA in the majority of cases. Low pH inhibited immunoglobulin reactivity with cultured H. pylori. CONCLUSIONS: Gastric H. pylori may evade humoral defense owing to poor deposition of immunoglobulin in the gastric environment or failure to express surface antigens that are present on cultured forms of H. pylori.

Whipple's disease.

Whipple's disease is a chronic systemic infectious disease caused by Tropheryma whippelii that typically involves the small intestine and causes malabsorption. Extraintestinal manifestations such as arthritis and fever are common and often exist prior to the onset of gastrointestinal symptoms. Involvement of the central nervous system can occur and lead to permanent sequelae. Weight loss, hyperpigmentation, and lymphadenopathy are frequent findings. The definitive diagnosis is made by biopsy of the small intestine mucosa which reveals infiltration of the lamina propria of the small intestine with periodic acid-Schiff positive macrophages. Treatment with trimethoprim combined with sulfamethoxazole for 1 year usually results in clinical remission and an excellent prognosis. Recent advances using molecular techniques to identify the uncultured bacillus of Whipple's disease should lead to a better understanding of the pathophysiology and allow for the development of a sensitive noninvasive diagnostic test.

Conventional cleaning and disinfection techniques eliminate the risk of endoscopic transmission of Helicobacter pylori.

OBJECTIVE: To determine whether endoscopes serve as a reservoir for Helicobacter pylori and whether two commonly used cleaning and disinfection methods eliminate the risk of H. pylori transmission. METHODS: A prospective study was carried out in 107 patients who were undergoing upper gastrointestinal endoscopy for routine clinical indications. H. pylori DNA was assayed by polymerase chain reaction (PCR) of endoscope washes before and after procedure, in gastric aspirates and in endoscope washes after cleaning and disinfection of endoscopes. Gastric biopsies were assayed by rapid urease test (CLOtest, Tri-Med Specialties Inc., Lenexa, KS) of two antral biopsies. RESULTS: Forty-one of 107 (38%) patients were H. pylori-positive by PCR. Endoscopes were contaminated after 25 of 41 (61%) H. pylori-positive procedures. However, 107 of 107 pre-endoscopy and postcleaning aspirates were negative, indicating that decontamination was 100% effective. The urease test was positive in 25 of 41 H. pylori-positive patients, a sensitivity of 61%. PCR was positive in 41 of 41 H. pylori-positive patients, a sensitivity of 100%. In 5 of 16 PCR-positive/urease-negative patients, the identification of H. pylori was clinically relevant. CONCLUSION: Endoscopes are frequently contaminated with H. pylori after endoscopy in H. pylori-infected patients, but conventional cleaning and disinfection techniques are highly effective in eliminating H. pylori. When appropriate negative control samples are obtained from the endoscope, PCR of endoscopic gastric aspirates appears to be a sensitive test that can detect clinically relevant H. pylori infection that is missed when only a rapid urease test is used.

Gastrocolic and duodenocolic fistulas in Crohn's disease.

Crohn's disease is a rare cause of gastrocolic and duodenocolic fistulas. Only 83 examples (27 gastric, 52 duodenal, four both) have been described. Weight loss, abdominal pain, and diarrhea are common features but fail to distinguish a fistula from active inflammatory bowel disease. Fecal vomiting is pathognomic but is present in one third of gastrocolic and only 2% of duodenocolic fistulas. Diagnosis is most readily made by contrast radiography, with barium enema being more sensitive than barium meal. Although several gastrocolic fistulas have been successfully treated with long-term 6-mercaptopurine, surgery is the mainstay of therapy. An isolated duodenocolic fistula should not be regarded as the primary indication for operation because most are asymptomatic. Ileocolonic resection with simple gastric or duodenal repair is safe and effective in most cases. An ileocolonic anastomosis should be positioned away from the stomach or duodenum or protected with omentum to prevent recurrent fistulization. A number of fistulas appear to have arisen from gastric or duodenal Crohn's, but the vast majority originate from diseased colon.

Ga-67 citrate in diagnosing tracheoesophageal fistula in a patient with AIDS. Case report.

Increased radiopharmaceutical uptake in the mediastinum and/or hilum on Ga-67 citrate scan in patients with AIDS has been attributed, to date, mostly to infectious etiologies. Because other complications are being reported in these patients, awareness of their presentation in diagnostic imaging is important. Tracheoesophageal fistula can also be accompanied by a focal area of increased uptake in the mediastinum. In this patient, a Ga-67 citrate scan was the first modality of diagnostic imaging to raise suspicion of such a diagnosis.