P. gingivalis Lipopolysaccharide Stimulates the Upregulated Expression of the Pancreatic Cancer-Related Genes Regenerating Islet-Derived 3 A/G in Mouse Pancreas.

Although epidemiological studies have shown a relationship between periodontal disease and pancreatic cancer, the molecular mechanisms involved remain unclear. In this study, the effects of systemic administration of Porphyromonas gingivalis lipopolysaccharide (PG-LPS) on gene expression were comprehensively explored in mouse pancreas that did not demonstrate any signs of inflammation. PG-LPS was prepared in physiological saline and intraperitoneally administered to male mice at a concentration of 5 mg/kg every 3 days for 1 month. After extracting total RNA from the excised mice pancreas, a comprehensive DNA microarray analysis of gene expression was performed. Tissue specimens were also subjected to hematoxylin-eosin staining and immunohistochemistry using anti-regenerating islet-derived 3A and G (Reg3A/G) antibody. ImageJ software was used to quantify the area of Reg3A/G positive cells in pancreatic islets by binarizing image date followed by area extraction. The results were compared using Mann-Whitney U test. Data are presented as mean ± standard deviation (SD) with p < 0.05 considered as significant. Reg3G, a gene related to pancreatic cancer, was one of the 10 genes with the highest levels of expression in the pancreas stimulated with PG-LPS. The comprehensive analysis revealed a 73-fold increase in Reg3G expression level in the PG-LPS group when compared with the control group; in addition, the expression level of Reg3A was increased by 11-fold in the PG-LPS group. Image analysis showed that the ratio of Reg3A/G positive cells was higher in the PG-LPS group than the control. Immunostaining showed the presence of Reg3A/G-positive cells in the alpha-cell equivalent areas around the islets of Langerhans in the PG-LPS group. These results support the notion that periodontal disease may be a risk factor for pancreatic cancer.

Identification of a periodontal pathogen and bihormonal cells in pancreatic islets of humans and a mouse model of periodontitis.

Results from epidemiological and prospective studies indicate a close association between periodontitis and diabetes. However the mechanisms by which periodontal pathogens influence the development of prediabetes/diabetes are not clear. We previously reported that oral administration of a periodontal pathogen, Porphyromonas gingivalis (Pg) to WT mice results in insulin resistance, hyperinsulinemia, and glucose intolerance and that Pg translocates to the pancreas. In the current study, we determined the specific localization of Pg in relation to mouse and human pancreatic α- and ß-cells using 3-D confocal and immunofluorescence microscopy and orthogonal analyses. Pg/gingipain is intra- or peri-nuclearly localized primarily in ß-cells in experimental mice and also in human post-mortem pancreatic samples. We also identified bihormonal cells in experimental mice as well as human pancreatic samples. A low percentage of bihormonal cells has intracellular Pg in both humans and experimental mice. Our data show that the number of Pg translocated to the pancreas correlates with the number of bihormonal cells in both mice and humans. Our findings suggest that Pg/gingipain translocates to pancreas, particularly ß-cells in both humans and mice, and this is strongly associated with emergence of bihormonal cells.

Impact of microbial contamination of the islet product during total pancreatectomy with islet autotransplantation.

BACKGROUND: The combined use of interleukin-1ß and tumor necrosis factor-α blockers in the peritransplant period has improved outcomes of total pancreatectomy with islet autotransplantation (TPIAT). However, these drugs may suppress the immune system, resulting in severe infection. METHODS: We retrospectively investigated the impact of microbial-contaminated islet product on posttransplant complications and metabolic outcomes of TPIAT patients receiving the IL-1ß and TNF-blockade treatment at our center. RESULTS: Among 108 TPIAT patients, 37 patients (34%) received contaminated products. Preoperative stent treatment and fibrosis score were independent risk factors for the contamination. There were no significant differences between the contaminated and noncontaminated product groups in posttransplant infectious complication rate, length of hospitalization, or readmission rate. However, islet equivalents (P < .0001) and insulin independence rate (P = .036) at 6 months were significantly lower for patients receiving contaminated product. CONCLUSIONS: These results suggest that combined anti-inflammatory drug use is safe and well tolerated in TPIAT patients who receive contaminated islet product and does not increase the rate of infectious complications; however, contaminated islet product is associated with poor metabolic outcomes.

Human Islet Response to Selected Type 1 Diabetes-Associated Bacteria: A Transcriptome-Based Study.

Type 1 diabetes (T1D) is a chronic autoimmune disease that results from destruction of pancreatic ß-cells. T1D subjects were recently shown to harbor distinct intestinal microbiome profiles. Based on these findings, the role of gut bacteria in T1D is being intensively investigated. The mechanism connecting intestinal microbial homeostasis with the development of T1D is unknown. Specific gut bacteria such as Bacteroides dorei (BD) and Ruminococcus gnavus (RG) show markedly increased abundance prior to the development of autoimmunity. One hypothesis is that these bacteria might traverse the damaged gut barrier, and their constituents elicit a response from human islets that causes metabolic abnormalities and inflammation. We have tested this hypothesis by exposing human islets to BD and RG in vitro, after which RNA-Seq analysis was performed. The bacteria altered expression of many islet genes. The commonly upregulated genes by these bacteria were cytokines, chemokines and enzymes, suggesting a significant effect of gut bacteria on islet antimicrobial and biosynthetic pathways. Additionally, each bacteria displayed a unique set of differentially expressed genes (DEGs). Ingenuity pathway analysis of DEGs revealed that top activated pathways and diseases included TREM1 signaling and inflammatory response, illustrating the ability of bacteria to induce islet inflammation. The increased levels of selected factors were confirmed using immunoblotting and ELISA methods. Our data demonstrate that islets produce a complex anti-bacterial response. The response includes both symbiotic and pathogenic aspects. Both oxidative damage and leukocyte recruitment factors were prominent, which could induce beta cell damage and subsequent autoimmunity.

Microbial Contamination, Infection, and Antimicrobial Use During Total Pancreatectomy With Islet Autotransplantation.

OBJECTIVES: Total pancreatectomy with islet autotransplantation can relieve pain associated with chronic pancreatitis while preserving islet function. Islet preparations are often contaminated by enteric flora. We assessed the impact of contaminated islet preparations on the prevalence of postoperative infection. METHODS: Electronic health records for patients who underwent total pancreatectomy with islet autotransplantation from August 1, 2011, to November 15, 2017 were retrospectively reviewed to compare the prevalence of postoperative infection in patients with a positive islet culture and islet culture negative patients. RESULTS: Sixty-one patients were included. Twenty-nine patients (47.5%) had a positive islet culture, and 23 (79.3%) of these patients received antimicrobial prophylaxis. The prevalence of postoperative infection did not differ between the islet culture positive and islet culture negative groups (41% vs 34%, P = 0.57). No infections occurred in the 6 islet culture positive patients who did not receive prophylaxis. No difference in intensive care unit or hospital length of stay or in 30-day or 90-day readmission rates were observed. CONCLUSIONS: Despite the common use of postoperative systemic antimicrobials, we observed no difference in the prevalence of postoperative infection, length of stay, or hospital readmission in patients receiving a contaminated islet preparation. If prophylactic antimicrobials are used, the duration should be minimized.

Pancreas preservation fluid microbial contamination is associated with poor islet isolation outcomes - a multi-centre cohort study.

The microbiological safety of islet preparations is paramount. Preservation medium contamination is frequent, and its impact on islet yield and function remains unclear. Microbiological samples collected during islet isolations from 2006 to 2016 were analyzed and correlated to isolation and allo- and autotransplantation outcomes. Microbial contamination of preservation medium was found in 64.4% of processed donor pancreases (291/452). We identified 464 microorganisms including Staphylococcus (253/464, 54.5%), Streptococcus (31/464, 6.7%), and Candida species (25/464, 5.4%). Microbial contamination was associated with longer warm and cold ischemia times and lower numbers of postpurification islet equivalents, purity, transplant rate, and stimulation index (all P < 0.05). Six percent of the preparations accepted for transplantation showed microbial contamination after isolation (12/200); 9 of 12 were Candida species. Six patients were transplanted with a sample with late microbial growth discovered after the infusion. Insulin independence rate was not affected. This risk of transplanting a contaminated islets preparation was reduced by half following the implementation of an additional sampling after 24 h of islet culture. Pancreas preservation fluid microbial contamination is associated with lower transplant rate and poorer in vitro function, but not with changes in graft survival. Culture medium testing 1 day after isolation reduces the risk of incidental transplantation with contaminated islets.

The impact of bacterial colonization on graft success after total pancreatectomy with autologous islet transplantation: considerations for early definitive surgical intervention.

OBJECTIVE: The purpose of this study was to determine whether bacterial contamination of islets affects graft success after total pancreatectomy with islet autotransplantation (TPIAT). BACKGROUND: Factors associated with insulin independence after TPIAT are inconclusive. Although bacterial contamination does not preclude transplantation, the impact of bacterial contamination on graft success is unknown. METHODS: Patients who received TPIAT at the University of Virginia between January 2007 and January 2016 were reviewed. Patient charts were reviewed for bacterial contamination and patients were prospectively contacted to assess rates of insulin independence. RESULTS: There was no significant difference in demographic or perioperative data between patients who achieved insulin independence and those who did not. However, six of 27 patients analyzed (22.2%) grew bacterial contaminants from culture of the final islet preparations. These patients had significantly lower islet yield and C-peptide at most recent follow-up (P<.05), and none of these patients achieved insulin independence. CONCLUSIONS: Islet transplant solutions are often culture positive, likely secondary to preprocurement pancreatic manipulation and introduction of enteric flora. Although autotransplantation of culture-positive islets is safe, it is associated with higher rates of graft failure and poor islet yield. Consideration should be given to identify patients who may develop refractory chronic pancreatitis and offer early operative management to prevent bacterial colonization.

Positive sterility cultures of transplant solutions during pancreatic islet autotransplantation are associated infrequently with clinical infection.

BACKGROUND: Chronic pancreatitis is a painful and often debilitating disease. Total pancreatectomy with intra-portal islet autotransplantation (TP-IAT) is a treatment option that allows for pain relief and preservation of beta-cell mass, thereby minimizing the complication of diabetes mellitus. Cultures of harvested islets are often positive for bacteria, possibly due to frequent procedures prior to TP-IAT, such as endoscopic retrograde cholangiopancreatography (ERCP), stenting, or other operative drainage procedures. It is unclear if these positive cultures contribute to post-operative infections. HYPOTHESIS: We hypothesized that positive cultures of transplant solutions will not be associated with increased infection risk. METHODS: We reviewed retrospectively the sterility cultures from both the pancreas preservation solution used to transport the pancreas and the final islet preparation for intra-portal infusion of patients who underwent TP-IAT between April 2006 and November 2012. Two hundred fifty-one patients underwent total, near-total, or completion pancreatectomy with IAT and had complete sterility cultures. All patients received prophylactic peri-operative antibiotics. Patients with positive pancreas preservation solution or islet sterility cultures received further antibiotics for 5-7 d. Patients' medical records were reviewed for post-operative infections and causative organisms. RESULTS: Of the 251 patients included, 151 (61%) had one or more positive bacterial cultures from the pancreas preservation solution or final islet product. Seventy-three of the 251 patients (29%) had an infectious complication. Thirty-four of the 73 (22%) patients with a post-operative infectious complication also had positive cultures. Only seven of 151 patients with positive cultures (4.7%) had an infectious complication caused by the same organism as that isolated from their pancreas or islet cell preparation. CONCLUSIONS: In autologous islet preparations, isolation solutions frequently have positive cultures, but this finding is associated infrequently with clinical infection.

Effects of Candida on insulin secretion of human adult pancreatic islets and possible onset of diabetes.

This study aims to determine the origin of Candida contamination of pancreatic tissue cultures, as well as its influence on insulin secretory activity of the pancreatic islets. Pancreatic tissue was obtained after pancreatectomy in patients who had chronic pancreatitis or benign tumours. Islets were isolated under aseptic conditions by a manual method. Microbiological analysis was performed by standard procedures and secretory activity was determined on the first, third and seventh day of cultivation. Insulin stimulation index (SI) on the first day of incubation was 0.665 +/- 0.082 and 0.982 +/- 0.167 for sterile and infected cultures, respectively (expressed as means +/- SE). On the third day of cultivation, the SI for sterile cultures was 0.645 +/- 0.071 while these value were higher in contaminated cultures (1.252 +/- 0.413). On the seventh day, SI was 0.853 +/- 0.032 and 1.239 +/- 0.169 for sterile and infected cultures, respectively (P = 0.05). Analysis of results for the first, third and seventh day of incubation and comparison of both groups showed that SI was 0.721 +/- 0.041 for sterile cultures, while for contaminated cultures it was higher by 37.68% (SI = 1.157 +/- 0.154; P = 0.01). The results show that cell culture contamination originates from an original pancreatic tissue infection, and that Candida can provoke an elevated level of insulin secretion in such patients, thus increasing chances for the onset of diabetes.

Autotransplantation of culture-positive islet product: is dirty always bad?

BACKGROUND: In selected patients, total pancreatectomy with islet autotransplantation (TPIAT) effectively relieves pain caused by chronic pancreatitis and ameliorates the brittle diabetes of the apancreatic state. Patients often undergo multiple endoscopic and surgical interventions prior to TPIAT, increasing the risk for pancreas colonization with enteric microorganisms. Little is known of the safety of transplanting islet cells with microbial contamination. METHODS: A prospectively collected database of 80 patients submitted to TPIAT at the Medical University of South Carolina from March 2009 to February 2012 was retrospectively reviewed. Patient charts were reviewed for postoperative infectious complications and organisms identified were compared with those identified in pre-transplant islet cultures. RESULTS: A total of 35 patients (43.8%) had a positive pre-transplant islet cell Gram stain or islet cell culture from the final islet preparation solution. Of these 35 patients, 33 (94.3%) were given antibiotics prophylactically post-transplant for a positive islet Gram stain or culture. Twenty patients (57.1%) receiving Gram stain- or culture-positive islets developed postoperative infectious complications, but only four patients (11.4%) developed infections that concorded with their pre-transplant islet product. CONCLUSIONS: Islet transplant solutions are frequently culture-positive, presumably as a result of prior pancreas intervention. Microbial contamination of islet preparations should not preclude autotransplantation.

On the etiology of type 1 diabetes: a new animal model signifying a decisive role for bacteria eliciting an adverse innate immunity response.

The cause of type 1 diabetes (T1D) remains unknown; however, a decisive role for environmental factors is recognized. The increased incidence of T1D during the last decades, as well as regional differences, is paralleled by differences in the intestinal bacterial flora. A new animal model was established to test the hypothesis that bacteria entering the pancreatic ductal system could trigger ß-cell destruction and to provide new insights to the immunopathology of the disease. Obtained findings were compared with those present in two patients dying at onset of T1D. Different bacterial species, present in the human duodenum, instilled into the ductal system of the pancreas in healthy rats rapidly induced cellular infiltration, consisting of mainly neutrophil polymorphonuclear cells and monocytes/macrophages, centered around the pancreatic ducts. Also, the islets of Langerhans attracted polymorphonuclear cells, possibly via release of IL-6, IL-8, and monocyte chemotactic protein 1. Small bleedings or large dilatations of the capillaries were frequently found within the islets, and several ß-cells had severe hydropic degeneration (ie, swollen cytoplasm) but with preserved nuclei. A novel rat model for the initial events in T1D is presented, revealing marked similarities with the morphologic findings obtained in patients dying at onset of T1D and signifying a decisive role for bacteria in eliciting an adverse innate immunity response. The present findings support the hypothesis that T1D is an organ-specific inflammatory disease.

Prevention of virus-induced type 1 diabetes with antibiotic therapy.

Microbes were hypothesized to play a key role in the progression of type 1 diabetes (T1D). We used the LEW1.WR1 rat model of Kilham rat virus (KRV)-induced T1D to test the hypothesis that the intestinal microbiota is involved in the mechanism leading to islet destruction. Treating LEW1.WR1 rats with KRV and a combination of trimethoprim and sulfamethoxazole (Sulfatrim) beginning on the day of infection protected the rats from insulitis and T1D. Pyrosequencing of bacterial 16S rRNA and quantitative RT-PCR indicated that KRV infection resulted in a transient increase in the abundance of Bifidobacterium spp. and Clostridium spp. in fecal samples from day 5- but not day 12-infected versus uninfected animals. Similar alterations in the gut microbiome were observed in the jejunum of infected animals on day 5. Treatment with Sulfatrim restored the level of intestinal Bifidobacterium spp. and Clostridium spp. We also observed that virus infection induced the expression of KRV transcripts and the rapid upregulation of innate immune responses in Peyer's patches and pancreatic lymph nodes. However, antibiotic therapy reduced the virus-induced inflammation as reflected by the presence of lower amounts of proinflammatory molecules in both the Peyer's patches and pancreatic lymph nodes. Finally, Sulfatrim treatment reduced the number of B cells in Peyer's patches and downmodulated adaptive immune responses to KRV, but did not interfere with antiviral Ab responses or viral clearance from the spleen, pancreatic lymph nodes, and serum. The data suggest that gut microbiota may be involved in promoting virus-induced T1D in the LEW1.WR1 rat model.

Microbiological safety of porcine islets: comparison with source pig.

BACKGROUND: Pig islet donors intended for clinical xenotransplantation for the treatment of diabetes must meet stringent conditions. Among others, viruses with the potential to cross the species barrier should be excluded from the herd: this list includes encephalomyocarditis virus (EMCV), hepatitis E virus (HEV), porcine cytomegalovirus (PCMV) and porcine γ-lymphotropic herpesvirus (PLHV). As an islet product is isolated from the pancreas and then subjected to culture before implantation, the question is raised whether islets could be negative even if the animal itself is positive for a distinct pathogen. METHODS: To answer this question, sensitive quantitative real-time PCR assays were established for EMCV, HEV, PCMV and PLHV. Twelve adult animals from a high-hygienic herd were then evaluated; testing tissues, where the virus is expected to reside in latent infection, testing islets immediately after isolation, and then isolated islets after a 7-day culture. RESULTS: None of the tissues tested positive for EMCV, HEV or PLHV. PCMV was observed in spleen tissue from six animals: three of these six animals were positive for isolated islets, and two of these three cases were also positive for islets after culture. Older animals in particular showed positivity, and within a given litter not all animals were PCMV positive. CONCLUSIONS: These data fit with spread through the herd by horizontal transmission, not in utero infection. PCMV has to be excluded from the herd to ensure that islets for transplantation are negative for PCMV.

Effects of bacterial infection on insulin secretory capacity of human adult pancreatic islets.

This study aims to determine the origin of bacterial contamination of pancreatic tissue cultures, as well as its influence on insulin secretory activity (expressed as stimulation index [SI]) of the pancreatic islets. Pancreatic tissue was obtained after pancreatectomy in patients who had chronic pancreatitis or benign tumours. Islets were isolated under aseptic conditions by a manual method. Microbiological analyses were performed by standard procedures and the SI was determined on the first and seventh day of cultivation. In cultures contamminated by Pseudomonas, SI was 1.58 +/- 1.16 on day 1 and 0.22 +/- 0.14 on day 7 (P<0.01). Cultures contaminated by Enterobacter showed an SI of 0.21 +/- 0.1 on day 1, which increased to 1.19 +/- 0.66 on day 7 (P<0.01). In cases of Staphylococcus contamination, SI was 0.07 +/- 0.05 on day 1 and 0.33 +/- 0.21 on day 7 (P<0.01). The study shows that cell culture contamination originates from an original pancreatic tissue infection. The presence of bacteria may reduce or increase insulin secretion in cell culture, depending on the type of microorganism, and this can provoke reduced or elevated levels of insulin secretion in recipients, thus increasing the chances for the onset of diabetes.

Detection of microbial contamination during human islet isolation.

Current good manufacturing practice (cGMP) islet processing facilities provide an ultraclean environment for the safe production of clinical grade islets for transplantation into immunosuppressed diabetic recipients. The objective of this study was to monitor the rate of microbial contamination in islet products after implementation of good manufacturing practice conditions. Fluid samples for microbial contamination were collected at the following steps: from the pancreas transport solution upon arrival of the organ (n=157), after surface decontamination of the pancreas with antiseptic agents (n=89), from islet supernatant at the end of the isolation (n=104), and from islet supernatant as a final transplantable product after culture (n=53). Bacterial, fungal, and mycoplasma cultures were conducted for 2, 2, and 3 weeks, respectively. Microbial contamination was detected in 31% of transport solution. The contamination was not associated with the presence of the duodenum during the preservation, cold ischemia time, or procurement team (local vs. distant). Surface decontamination of the pancreas resulted in clearance of 92% of the microbial contamination. Six preparations at the end of the isolation revealed microbial growth. All were de novo contamination during the processing. Fifty-three preparations that met our release criteria in terms of product sterility were transplanted into type 1 diabetic patients. In two instances, positive culture of the islet preparation was reported after transplantation had occurred. No patient showed any clinical findings suggestive of infection or any radiological abnormalities suggestive of abscess; a single dose of antibiotic coverage was given routinely to recipients prior to islet infusion. Although transport solution carries a high risk of microbial contamination, most contaminants become undetectable during islet processing. Microbial contamination in final products is rare, but de novo contamination still occurs during processing even under cGMP conditions.

The use of pancreas biopsy scoring provides reliable porcine islet yields while encapsulation permits the determination of microbiological safety.

For clinical xenogenic islet transplantation to be successful, several requirements must be met. Among them is a sizeable and reliable source of fully functional and microbiologically safe islets. The inherent variability among porcine pancreases, with respect to islet yield, prompted us to develop a Biopsy Score technique to determine the suitability of each pancreas for islet isolation processing. The Biopsy Score consists of an assessment of five variables: warm ischemia time, pancreas color, fat content, islet size, and islet demarcation, each of which is assigned a value of -1 or +1, depending on whether or not the established criteria is met. For determination of islet size and demarcation, fresh biopsies of porcine pancreases are stained with dithizone (DTZ) solution and examined under a dissecting microscope. Based on the scoring of such biopsies in pancreases from 26-56-month-old sows, we report here that the presence of large (>100 microm diameter), well-demarcated islets in the pancreas biopsy is a reliable predictor of isolation success. Encapsulation of the isolated porcine islets within the inner layer of a 1.5% agarose and an outer layer of 5.0% agarose macrobead, containing 500 equivalent islet number (EIN), provides for extended in vitro functional viability (>6 months of insulin production in response to glucose), as well as for comprehensive microbiological testing and at least partial isolation of the xenogeneic islets from the host immune system. All microbiological testing to date has been negative, except for the presence of porcine endogenous retrovirus (PERV). Taken together, we believe that the Biopsy Score enhancement of our islet isolation technique and our agarose-agarose macroencapsulation methodology bring us significantly closer to realizing clinical porcine islet xenotransplantation for the treatment of insulin-dependent diabetic patients.

Clinical significance of bacterial cultures from 28 autologous islet cell transplant solutions.

PURPOSE: Total pancreatectomy and autologous islet cell transplantation are being investigated as a novel surgical treatment for patients with chronic pancreatitis. Preliminary data has demonstrated the presence of enteric bacteria in solutions used to harvest islet cells. Subsequently, we started culturing autologous islet solutions to determine whether any concordance existed between these cultures and postoperative infectious complications. METHODS: A retrospective analysis evaluated microbiologic cultures between July 2000 and November 2003; 33 patients underwent total or completion pancreatectomy and islet cell transplantation. Five patients were excluded due to incomplete culture data. Aerobic, anaerobic and fungal cultures were performed on all islet preparation solutions. Patient charts were examined for postoperative infectious complications. Microbiologic data from these infections was compared to pretransplant islet cultures. Islet cells from each patient were tested in vitrofor both function and viability. RESULTS: Of the 28 patients, 25 (89.3%) had bacterial culture-positive media solutions. Only 4 patients (14.3%) had an infectious complication from which bacteria was isolated that corresponded to bacteria in their islet cell preparation. In vitro islet cell viability was greater than 95% in the pretransplant aliquots. CONCLUSION: These results suggest that transplantation of bacterial-positive islet cell solutions does not appear to increase the risk of postoperative infectious complications or impact islet cell viability. Therefore, prolonged antibiotic treatment against these specific bacteria beyond the perioperative period does not seem warranted.

Microbial surveillance during human pancreatic islet isolation.

The aim of the study was to investigate microbiological contamination rate during human pancreatic islet isolation. Between 1996 and 2002, pancreas preservation media and post-purification islet preparations were screened for microbiological contamination. After arrival in the laboratory, pancreata were washed prior to enzyme perfusion with either Hank's balanced salt solution (Group I, n = 170, 1996 to 2001) or decontaminated with polyvidonum-iodine, cefazoline, and amphotericine B (Group II, n = 45, 2001 to 2002). Microbiological contamination of preservation media was observed in 56% and 84% for Groups I and II, respectively. Analysis of contaminants revealed 74% Gram-positive, 21% Gram-negative bacteria and 5% fungi. Duration of transport had an influence on the rate of contamination (P < 0.05). After islet isolation, Group I presented microbial contamination of 16 islet preparations (9.4%) [i.e. Gram-positive bacteria (n = 10), Gram-negative bacteria (n = 4), and fungi (n = 2)]. In Group II, only 2 islet preparations (4.4%) presented microbial contamination. Microbial contamination during pancreas procurement occurs frequently. Most microorganisms are eliminated during islet isolation, and de novo contaminations during islet isolation are rare. Pancreas decontamination reduces the risk of infection of the final islet preparation.

Do microbes have a causal role in type 1 diabetes?

Type 1 diabetes mellitus (T1DM) results from environmental factors acting on genetically susceptible individuals. Microbial infections and their immunological consequences are suspected to take part in the pathogenesis of T1DM. Congenital rubella infection has been strongly associated with increased disease susceptibility. In addition, infections with different strains of enteroviruses, human cytomegalovirus, and rotavirus have been suggested to be diabetogenic in susceptible individuals. A newly emerged hypothesis states that a bacterial toxin, bafilomycin A1 produced by Streptomyces spp, could be the cause of pancreatic beta-cell damage. In some instances, microbial infections may even protect the individual from T1DM. There are several proposed mechanisms of beta-cell damage caused by microbes. T1DM can result from direct cytolysis of beta-cells. Other suggested mechanisms are cross-reactivity between microbial proteins and self antigens (molecular mimicry), bystander activation of lymphocytes, and alterations in cytokine concentrations affecting T-helper cell balance in the vicinity of pancreatic beta-cells. Proving a causal role between microbial infections and T1DM appears difficult. Despite intensive research, a final conclusion concerning the causal role of microbes in the pathogenesis of T1DM has not been made.

Salmonella typhimurium infection halts development of type 1 diabetes in NOD mice.

Infectious disease has been proposed as an environmental modifier of autoimmunity in both human populations and the NOD mouse. We found that infection of NOD mice with attenuated, but not killed, Salmonella typhimurium can reduce the incidence of type 1 diabetes (T1D), even if infection occurs after the development of a peri-islet pancreatic infiltrate. Functional diabetogenic effector T cells are still present, as demonstrated by the initiation of diabetes in NOD-scid recipients of transferred splenocytes. High levels of IFN-gamma are secreted by splenocytes of infected mice, but there is no evidence of involvement of IL-10 in the protective effect of the infection. Finally, prolonged changes in cell subsets are observed in infected mice involving invariant Valpha14Jalpha281 NuKappaTau and dendritic cells. These data reinforce the idea that prevention of T1D in the NOD mouse cannot be reduced to the simple Th1/Th2 paradigm and that different infections may involve different protective mechanisms.