Evidence and Role for Bacterial Mucin Degradation in Cystic Fibrosis Airway Disease.

Chronic lung infections in cystic fibrosis (CF) patients are composed of complex microbial communities that incite persistent inflammation and airway damage. Despite the high density of bacteria that colonize the lower airways, nutrient sources that sustain bacterial growth in vivo, and how those nutrients are derived, are not well characterized. In this study, we examined the possibility that mucins serve as an important carbon reservoir for the CF lung microbiota. While Pseudomonas aeruginosa was unable to efficiently utilize mucins in isolation, we found that anaerobic, mucin-fermenting bacteria could stimulate the robust growth of CF pathogens when provided intact mucins as a sole carbon source. 16S rRNA sequencing and enrichment culturing of sputum also identified that mucin-degrading anaerobes are ubiquitous in the airways of CF patients. The collective fermentative metabolism of these mucin-degrading communities in vitro generated amino acids and short chain fatty acids (propionate and acetate) during growth on mucin, and the same metabolites were also found in abundance within expectorated sputum. The significance of these findings was supported by in vivo P. aeruginosa gene expression, which revealed a heightened expression of genes required for the catabolism of propionate. Given that propionate is exclusively derived from bacterial fermentation, these data provide evidence for an important role of mucin fermenting bacteria in the carbon flux of the lower airways. More specifically, microorganisms typically defined as commensals may contribute to airway disease by degrading mucins, in turn providing nutrients for pathogens otherwise unable to efficiently obtain carbon in the lung.

Genome-Wide Survey of Pseudomonas aeruginosa PA14 Reveals a Role for the Glyoxylate Pathway and Extracellular Proteases in the Utilization of Mucin.

Chronic airway infections by the opportunistic pathogen Pseudomonas aeruginosa are a major cause of mortality in cystic fibrosis (CF) patients. Although this bacterium has been extensively studied for its virulence determinants, biofilm growth, and immune evasion mechanisms, comparatively little is known about the nutrient sources that sustain its growth in vivo Respiratory mucins represent a potentially abundant bioavailable nutrient source, although we have recently shown that canonical pathogens inefficiently use these host glycoproteins as a growth substrate. However, given that P. aeruginosa, particularly in its biofilm mode of growth, is thought to grow slowly in vivo, the inefficient use of mucin glycoproteins may be relevant to its persistence within the CF airways. To this end, we used whole-genome fitness analysis, combining transposon mutagenesis with high-throughput sequencing, to identify genetic determinants required for P. aeruginosa growth using intact purified mucins as a sole carbon source. Our analysis reveals a biphasic growth phenotype, during which the glyoxylate pathway and amino acid biosynthetic machinery are required for mucin utilization. Secondary analyses confirmed the simultaneous liberation and consumption of acetate during mucin degradation and revealed a central role for the extracellular proteases LasB and AprA. Together, these studies describe a molecular basis for mucin-based nutrient acquisition by P. aeruginosa and reveal a host-pathogen dynamic that may contribute to its persistence within the CF airways.

The Effect of Comorbidities on Discharge Disposition and Readmission for Total Joint Arthroplasty Patients.

BACKGROUND: As the annual demand and number of total joint arthroplasty cases increase, so do concerns of outcomes of patient with specific comorbidities relative to outcomes and costs of care. METHODS: The study cohort included 2009 primary total knee arthroplasty (TKA) patients and 905 total hip arthroplasty patients. Discharge disposition was classified as discharge to any facility or home. The comorbidities of the patients who were readmitted and those without a 90-day event were also evaluated. RESULTS: In the TKA population, age, female gender, nonsmoking status, venous thromboembolism (VTE) history, and diabetes were significantly associated with discharge to extended care facility (ECF) on univariate analysis, unlike body mass index. With multivariate analyses, female gender, age, VTE history, and diabetes were associated with ECF placement, but smoking was not. In the total hip arthroplasty population, age, female gender, and nonsmoking status were significantly associated with discharge to ECF on univariate analysis, whereas body mass index, diabetes, and VTE history were not. On multivariate analyses, female gender and age were associated with ECF, but smoking was not. The only significant finding for the readmission data was an increased rate of readmission for TKA patients of older age. CONCLUSION: The potential of projecting patient discharge and readmission allows physicians to counsel patients and improve patient expectations.

Impact of medical or surgical admission on outcomes of patients with acute cholecystitis.

BACKGROUND: Although acute cholecystitis (AC) is a surgical disease, patients with the condition may be admitted to medical-related services (MS). This may lead to delayed cholecystectomy thereby affecting outcomes and quality of care. METHODS: Between July 2010 and March 2013, 329 patients under 70 years old presented to a community-based tertiary care hospital with AC and underwent same admission cholecystectomy. Outcomes were compared between patients admitted to MS and surgical services (SS). RESULTS: Two hundred fifteen patients (65.3%) were admitted to a MS. Patients under the MS had longer LOS (3.0 days vs. 2.0 days, p < 0.001), waiting time to surgical consultation (7.3 h vs. 5.0 h, p < 0.001) and to cholecystectomy (1.0, 0-2 days vs. 1.0, 0-1 day, p < 0.001), and increased hospital costs ($3685 vs. $4,688, p < 0.001) compared to the SS. Readmission and mortality rates were not significantly different between groups. CONCLUSION: Patients under 70 years old with AC undergoing cholecystectomy admitted to MS had increased LOS, delay to the operation, and hospital costs compared to those admitted to a SS. Admission of patients with AC to a SS needs to be emphasized to reduce costs and improve quality of care.

Decreased coenzyme A levels in ridA mutant strains of Salmonella enterica result from inactivated serine hydroxymethyltransferase.

The RidA/Yer057/UK114 family of proteins is well represented across the domains of life and recent work has defined both an in vitro activity and an in vivo role for RidA. RidA proteins have enamine deaminase activity, and in their absence the reactive 2-aminoacrylate (2-AA) accumulates and inactivates at least some pyridoxal 5'-phosphate (PLP)-containing enzymes in Salmonella enterica. The conservation of RidA suggested that 2-AA was a ubiquitous cellular stressor that was generated in central metabolism. Phenotypically, strains of S. enterica that lack RidA accumulated significantly more pyruvate in the growth medium than wild-type strains. Here we dissected this ridA mutant phenotype and showed it was an indirect consequence of damage to serine hydroxymethyltransferase (GlyA; E.C. 2.1.2.1). The results here identified a fourth PLP enzyme as a target of enamine stress in Salmonella.

Peer review journal publication rates of award-winning presentations from a multi-disciplinary multi-institutional medical education consortium annual research forum: 40-year experience.

INTRODUCTION: Resident research has been mandated by the Accreditation Council of Graduate Medical Education across all specialties. Southeast Michigan Center for Medical Education (SEMCME) has an annual Research Forum for resident competition, and we assessed the publication status of award-winning presentations. METHODS: The SEMCME Research Forum's winning presentations from 1978 to 2018 were reviewed. The author's information and keywords from the abstract's title were used to search PubMed and Google Scholar databases for publications. Descriptive statistics were generally used to characterize the data. RESULTS: Of 147 winning projects, 62% (78/126) were oral and 48% (10/21) were poster presentations; 88 (60%) were published. Obstetrics and gynecology had the highest publication rate (71%), followed by surgical (61%) and medical specialties (48%). CONCLUSION: While 60% of the award-winning presentations at the SEMCME Research Forum were published, more work needs to be done to examine the barriers preventing the publication of the remaining projects.

Predictors of Intensive Care Unit Admissions in Patients Presenting with Coronavirus Disease 2019.

Background Increased mortality rates among coronavirus disease 2019 (COVID-19) positive patients admitted to intensive care units (ICUs) highlight a compelling need to establish predictive criteria for ICU admissions. The aim of our study was to identify criteria for recognizing patients with COVID-19 at elevated risk for ICU admission. Methods We identified patients who tested positive for COVID-19 and were hospitalized between March and May 2020. Patients' data were manually abstracted through review of electronic medical records. An ICU admission prediction model was derived from a random sample of half the patients using multivariable logistic regression. The model was validated with the remaining half of the patients using c-statistic. Results We identified 1,094 patients; 204 (18.6%) were admitted to the ICU. Correlates of ICU admission were age, body mass index (BMI), quick Sequential Organ Failure Assessment (qSOFA) score, arterial oxygen saturation to fraction of inspired oxygen ratio, platelet count, and white blood cell count. The c-statistic in the derivation subset (0.798, 95% confidence interval [CI]: 0.748, 0.848) and the validation subset (0.764, 95% CI: 0.706, 0.822) showed excellent comparability. At 22% predicted probability for ICU admission, the derivation subset estimated sensitivity was 0.721, (95% CI: 0.637, 0.804) and specificity was 0.763, (95% CI: 0.722, 0.804). Our pilot predictive model identified the combination of age, BMI, qSOFA score, and oxygenation status as significant predictors for ICU admission. Conclusion ICU admission among patients with COVID-19 can be predicted by age, BMI, level of hypoxia, and severity of illness.

In the absence of RidA, endogenous 2-aminoacrylate inactivates alanine racemases by modifying the pyridoxal 5'-phosphate cofactor.

Members of the RidA (YjgF/YER057c/UK114) protein family are broadly conserved across the domains of life. In vitro, these proteins deaminate 3- or 4-carbon enamines that are generated as mechanistic intermediates of pyridoxal 5'-phosphate (PLP)-dependent serine/threonine dehydratases. The three-carbon enamine 2-aminoacrylate can inactivate some enzymes by forming a covalent adduct via a mechanism that has been well characterized in vitro. The biochemical activity of RidA suggested that the phenotypes of ridA mutant strains were caused by the accumulation of reactive enamine metabolites. The data herein show that in ridA mutant strains of Salmonella enterica, a stable 2-aminoacrylate (2-AA)/PLP adduct forms on the biosynthetic alanine racemase, Alr, indicating the presence of 2-aminoacrylate in vivo. This study confirms the deleterious effect of 2-aminoacrylate generated by metabolic enzymes and emphasizes the need for RidA to quench this reactive metabolite.

Conserved YjgF protein family deaminates reactive enamine/imine intermediates of pyridoxal 5'-phosphate (PLP)-dependent enzyme reactions.

The YjgF/YER057c/UK114 family of proteins is conserved in all domains of life, suggesting that the role of these proteins arose early and was maintained throughout evolution. Metabolic consequences of lacking this protein in Salmonella enterica and other organisms have been described, but the biochemical function of YjgF remained unknown. This work provides the first description of a conserved biochemical activity for the YjgF protein family. Our data support the conclusion that YjgF proteins have enamine/imine deaminase activity and accelerate the release of ammonia from reactive enamine/imine intermediates of the pyridoxal 5'-phosphate-dependent threonine dehydratase (IlvA). Results from structure-guided mutagenesis experiments suggest that YjgF lacks a catalytic residue and that it facilitates ammonia release by positioning a critical water molecule in the active site. YjgF is renamed RidA (reactive intermediate/imine deaminase A) to reflect the conserved activity of the protein family described here. This study, combined with previous physiological studies on yjgF mutants, suggests that intermediates of pyridoxal 5'-phosphate-mediated reactions may have metabolic consequences in vivo that were previously unappreciated. The conservation of the RidA/YjgF family suggests that reactive enamine/imine metabolites are of concern to all organisms.

Analysis and implications of changing hepatopancreatobiliary (HPB) case loads in general surgery residency training for HPB surgery accreditation.

OBJECTIVE: This study was conducted to determine whether residents are receiving enough hepatopancreatobiliary (HPB) training during general surgery residencies to exclude the necessity of pursuing formal fellowships in HPB surgery. METHODS: Trends in HPB surgery training were examined using Accreditation Council for Graduate Medical Education (ACGME) operative log data for the academic years 1999/2000 to 2009/2010. RESULTS: Of 800,000 HPB operations performed annually in the USA, the proportion of HPB procedures performed by general surgery residents increased from 15% (122,007) to 18% (143,000) between the periods under study. Numbers of pancreatic, liver and biliary procedures performed by graduating general surgery residents increased by 47% (from 8185 to 12,006), 31% (from 7468 to 9765), and 14% (from 106,354 to 121,239), respectively. The mean number of operations undertaken by a graduating resident increased from 8.3 to 11.5 (38% increase) for pancreatic surgeries, from 7.6 to 9.4 (24% increase) for liver surgeries, and from 107.5 to 116.6 (8% increase) for biliary surgeries. Total numbers of complex pancreatic, liver and biliary procedures increased by 91% (from 4768 to 9129) and 24% (from 6649 to 8233), and decreased by 29% (from 6581 to 4648), respectively. CONCLUSIONS: The overall trend shows an increase in the number of HPB procedures undertaken by graduating general surgery residents. The mean number of procedures exceeds ACGME requirements, but falls short of association guidelines. However, certain residents exceed International Hepato-Pancreato-Biliary Association (IHPBA) fellowship requirements for total and complex procedures during residency. Consideration should be given to those residents to allow them to bypass fellowship training provided that they meet other IHPBA standards.

Incentives as a Driving Force for Scholarly Activity in General Surgery Training: Survey of Program Directors and our Institution's Experience.

INTRODUCTION: Scholarly activity in a few of the domains is required for both residents and faculty per Accreditation Council for Graduate Medical Education's Common Program Requirements. Increased burden in clinical activities and economic changes in the health care environment have created new challenges, which have negatively affected faculty and residents to participate in scholarly activity. Various avenues are being sought which might help in improving the scholarly activity in an institution by providing dedicated time, salaried positions, grants, paid conferences, and financial incentives. METHODS: A survey was sent to program directors of surgery residency programs in 2020 to evaluate the impact of financial incentives on scholarly activity. Data was analyzed on SPSS 20, and descriptive statistics using frequencies and percentages were done. RESULTS: Out of 230 surveys sent, 80 (35%) program directors responded (35%). 52 (65%) of respondents were from university hospitals and 28 (35%) were from community hospitals. Both the faculty and residents were required to publish in 56 (70%) of the institutions surveyed. 59 (73.7%) considered a PubMed publication as a scholarly activity. Only 9 (11%) programs were supportive of residents being involved in research activities that had a designated rotation. 48 (60%) respondents stated that residents and faculty would be more likely to pursue research endeavors if they were provided some form of financial incentive, but only 9 (11%) had some sort of incentive program in place. CONCLUSION: Given the results of the survey, there is a need to seek uniform, acceptable, and sustainable alternative incentive programs to help promote and increase the scholarly activity of residents and faculty.

Publication rates of annual Research Day abstracts in peer-reviewed journals by residents and fellows at a community-based institution - A 10-year review of data and analysis.

Introduction: Research and publications are becoming increasingly important for residents who want to match into competitive fellowship training programs and fellows looking to optimize career opportunities. Institutional Research Days provide trainees the opportunity to gain presentation experience and feedback about their studies. We evaluated all abstracts that were presented at Ascension Providence Hospital (APH) during Research Day over a 10-year period to determine publication rates of manuscripts in peer-reviewed journals. Methods: Research abstracts presented by both residents and fellows during Research Days at APH from 2009 to 2018 were reviewed. Abstracts were classified by type of project, type of presentation, trainee, winners and non-winners, and training program. Winners were defined as abstracts which won first, second and third place awards. Publication of manuscripts was evaluated by searching PubMed and Google Scholar. Fisher's Exact test was used to analyze categorical data and Student's t-test was used to analyze continuous data; p < 0.05 was considered significant. Results: A total of 491 research and case report abstracts were presented by residents and fellows during Research Day over 10 years. For residents, 346 abstracts were presented; 25% (n = 85) were winners. The majority (51%) of winning abstracts were published, but only 26% of non-winning abstracts were published (p < 0.0001). More of both winning research oral (65%) and poster abstracts (61%) were published than non-winning oral (41%) and poster abstracts (22%, p = 0.02 and p = 0.0001, respectively), but publication rates for case reports were similar. The vast majority of published winning oral (88%) and poster abstracts (74%) came from the surgical programs. Fellows presented 145 abstracts; 30% (n = 43) were winners. A slightly higher percentage of winning abstracts (42%) were published compared to non-winning abstracts (32%, p = 0.3). Unlike the residents, the fellows had no significant publication rate differences between winning and non-winning research oral, research poster or case report abstracts, or between medical and non-medical subspecialties. Conclusions: Despite their award-winning presentations, residents and fellows published less than half of these projects and less than a third of non-award-winning projects. However, most publications came from the surgical specialties, indicating the colleagues in the medical specialties were not publishing. Further data are needed to identify factors that can improve a trainee's chances of being published in a peer-reviewed journal.

Corrigendum to "Determinants of all-cause in-hospital mortality among patients who presented with COVID-19 to a community teaching hospital in Michigan" [Heliyon 7 (12) (December 2021), Article e08566].

[This corrects the article DOI: 10.1016/j.heliyon.2021.e08566.].

Efficacy of HLA-DRB1∗03:01 and H2E transgenic mouse strains to correlate pathogenic thyroglobulin epitopes for autoimmune thyroiditis.

Thyroglobulin (Tg), a homodimer of 660 kD comprising 2748 amino acids, is the largest autoantigen known. The prevalence of autoimmune thyroid disease, including Hashimoto's thyroiditis and Graves' disease, has provided the impetus for identifying pathogenic T cell epitopes from human Tg over two decades. With no known dominant epitopes, the search has long been a challenge for investigators. After identifying HLA-DRB1∗03:01 (HLA-DR3) and H2E(b) as susceptibility alleles for Tg-induced experimental autoimmune thyroiditis in transgenic mouse strains, we searched for naturally processed T cell epitopes with MHC class II-binding motif anchors and tested the selected peptides for pathogenicity in these mice. The thyroiditogenicity of one peptide, hTg2079, was confirmed in DR3 transgenic mice and corroborated in clinical studies. In H2E(b)-expressing transgenic mice, we identified three T cell epitopes from mouse Tg, mTg179, mTg409 and mTg2342, based on homology to epitopes hTg179, hTg410 and hTg2344, respectively, which we and others have found stimulatory or pathogenic in both DR3- and H2E-expressing mice. The high homology among these peptides with shared presentation by DR3, H2E(b) and H2E(k) molecules led us to examine the binding pocket residues of these class II molecules. Their similar binding characteristics help explain the pathogenic capacity of these T cell epitopes. Our approach of using appropriate human and murine MHC class II transgenic mice, combined with the synthesis and testing of potential pathogenic Tg peptides predicted from computational models of MHC-binding motifs, should continue to provide insights into human autoimmune thyroid disease.

Determinants of all-cause in-hospital mortality among patients who presented with COVID-19 to a community teaching hospital in Michigan.

BACKGROUND & OBJECTIVES: Race plays an important role in healthcare disparities, often resulting in worse health outcomes. It is unclear if other patient factors and race interactions may influence mortality in patients with COVID-19. We aimed to evaluate how multiple determinants of all-cause in-hospital mortality from COVID-19 were linked to race. METHODS: A retrospective observational study was conducted at two hospitals in metropolitan Detroit. We identified patients aged ≥18 years-old who had tested positive for COVID-19 and were admitted between March 9 through May 16, 2020. Multivariable logistic regression was performed assessing predictors of all-cause in-hospital mortality in COVID-19. RESULTS: We identified 1064 unique patients; 74% were African Americans (AA). The all-cause in-hospital mortality was 21.7%, with the majority of deaths seen in AA (65.4%, P = 0.002) and patients 80 years or older (52%, P < 0.0001). AA women had lower all-cause mortality than AA men, white women, and white men based on race-gender interactions. In multivariable logistic regression analysis, older age (>80-year-old), dementia, and chronic kidney disease were associated with worse all-cause in-hospital mortality. Adjusted for race and body mass index (BMI), the main odds ratios (OR) and 95% confidence intervals (CI) are: Age 80 and older vs < 60 in females: OR = 7.4, 95% CI: 2.9, 18.7; in males OR = 7.3, 95% CI: 3.3, 16.2; Chronic Kidney Disease (CKD): OR = 1.7, 95% CI: 1.2, 2.6; Dementia: OR = 2.2, 95% CI: 1.5, 3.3. CONCLUSION: Gender significantly modified the association of race and COVID-19 mortality. African American females had the lowest all-cause in-hospital mortality risk compared to other gender-race groups.

Substrate-level phosphorylation is the primary source of energy conservation during anaerobic respiration of Shewanella oneidensis strain MR-1.

It is well established that respiratory organisms use proton motive force to produce ATP via F-type ATP synthase aerobically and that this process may reverse during anaerobiosis to produce proton motive force. Here, we show that Shewanella oneidensis strain MR-1, a nonfermentative, facultative anaerobe known to respire exogenous electron acceptors, generates ATP primarily from substrate-level phosphorylation under anaerobic conditions. Mutant strains lacking ackA (SO2915) and pta (SO2916), genes required for acetate production and a significant portion of substrate-level ATP produced anaerobically, were tested for growth. These mutant strains were unable to grow anaerobically with lactate and fumarate as the electron acceptor, consistent with substrate-level phosphorylation yielding a significant amount of ATP. Mutant strains lacking ackA and pta were also shown to grow slowly using N-acetylglucosamine as the carbon source and fumarate as the electron acceptor, consistent with some ATP generation deriving from the Entner-Doudoroff pathway with this substrate. A deletion strain lacking the sole F-type ATP synthase (SO4746 to SO4754) demonstrated enhanced growth on N-acetylglucosamine and a minor defect with lactate under anaerobic conditions. ATP synthase mutants grown anaerobically on lactate while expressing proteorhodopsin, a light-dependent proton pump, exhibited restored growth when exposed to light, consistent with a proton-pumping role for ATP synthase under anaerobic conditions. Although S. oneidensis requires external electron acceptors to balance redox reactions and is not fermentative, we find that substrate-level phosphorylation is its primary anaerobic energy conservation strategy. Phenotypic characterization of an ackA deletion in Shewanella sp. strain MR-4 and genomic analysis of other sequenced strains suggest that this strategy is a common feature of Shewanella.

Venous thromboembolism: management by American Association of Hip and Knee Surgeons.

A 2008 survey of American Association of Hip and Knee Surgeons membership explored current venous thromboembolism (VTE) protocols for lower-extremity total joint surgery. Fifty-three percent reported a change in VTE-related practices in the last 5 years. More than 70% reported that their primary hospital now mandates VTE prophylaxis. Although 74% of their primary hospitals recognized the American College of Chest Physicians guidelines, 68% of surgeons felt the American Academy of Orthopaedic Surgeons guidelines were more relevant to their practice. Respondents believe low molecular weight heparin to be the most efficacious but aspirin to be the easiest to use and has the lowest risks of bleeding and wound drainage. Warfarin was the most used in hospital prophylaxis, and 90% of respondents targeted an international normalized ratio of 1.6 to 2.5. Practice patterns continue to evolve, and there remains no consensus on specific treatment protocols or preferences.

Disruption of Cross-Feeding Inhibits Pathogen Growth in the Sputa of Patients with Cystic Fibrosis.

A critical limitation in the management of chronic polymicrobial infections is the lack of correlation between antibiotic susceptibility testing (AST) and patient responses to therapy. Underlying this disconnect is our inability to accurately recapitulate the in vivo environment and complex polymicrobial communities in vitro However, emerging evidence suggests that, if modeled and tested accurately, interspecies relationships can be exploited by conventional antibiotics predicted to be ineffective by standard AST. As an example, under conditions where Pseudomonas aeruginosa relies on cocolonizing organisms for nutrients (i.e., cross-feeding), multidrug-resistant P. aeruginosa may be indirectly targeted by inhibiting the growth of its metabolic partners. While this has been shown in vitro using synthetic bacterial communities, the efficacy of a "weakest-link" approach to controlling host-associated polymicrobial infections has not yet been demonstrated. To test whether cross-feeding inhibition can be leveraged in clinically relevant contexts, we collected sputa from cystic fibrosis (CF) subjects and used enrichment culturing to isolate both P. aeruginosa and anaerobic bacteria from each sample. Predictably, both subpopulations showed various antibiotic susceptibilities when grown independently. However, when P. aeruginosa was cultured and treated under cooperative conditions in which it was dependent on anaerobic bacteria for nutrients, the growth of both the pathogen and the anaerobe was constrained despite their intrinsic antibiotic resistance profiles. These data demonstrate that the control of complex polymicrobial infections may be achieved by exploiting obligate or facultative interspecies relationships. Toward this end, in vitro susceptibility testing should evolve to more accurately reflect in vivo growth environments and microbial interactions found within them.IMPORTANCE Antibiotic efficacy achieved in vitro correlates poorly with clinical outcomes after treatment of chronic polymicrobial diseases; if a pathogen demonstrates susceptibility to a given antibiotic in the lab, that compound is often ineffective when administered clinically. Conversely, if a pathogen is resistant in vitro, patient treatment with that same compound can elicit a positive response. This discordance suggests that the in vivo growth environment impacts pathogen antibiotic susceptibility. Indeed, here we demonstrate that interspecies relationships among microbiotas in the sputa of cystic fibrosis patients can be targeted to indirectly inhibit the growth of Pseudomonas aeruginosa The therapeutic implication is that control of chronic lung infections may be achieved by exploiting obligate or facultative relationships among airway bacterial community members. This strategy is particularly relevant for pathogens harboring intrinsic multidrug resistance and is broadly applicable to chronic polymicrobial airway, wound, and intra-abdominal infections.

Autoimmune thyroiditis: a model uniquely suited to probe regulatory T cell function.

Murine experimental autoimmune thyroiditis (EAT) is a model for Hashimoto's thyroiditis that has served as a prototype of T cell-mediated autoimmunity for more than three decades. Key roles for MHC restriction and autoantigen influence on susceptibility to autoimmunity have been demonstrated in EAT. Moreover, it has served a unique role in investigations of self tolerance. In the early 1980s, self tolerance and resistance to EAT induction could be enhanced by increasing circulating levels of the autoantigen, thyroglobulin (Tg), by exogenous addition as well as endogenous release. This observation, directly linking circulating self antigen to self tolerance, led to subsequent investigations of the role of regulatory T cells (Tregs) in self tolerance. These studies revealed that protection against autoimmunity, in both naive and tolerized mice, was mediated by thymically-derived CD4(+)CD25(+)Foxp3(+) Tregs. Moreover, these naturally-existing Tregs required proper costimulation, in context with autoantigen presentation, to maintain and enhance self tolerance. In particular was the selected use of MHC- and heterologous Tg-restricted models from both conventional and transgenic mice. These models helped to elucidate the complex interplay between autoantigen presentation and MHC class II-mediated T cell selection in the development of Treg and autoreactive T cell repertoires determining susceptibility to autoimmunity. Here we describe these investigations in further detail, providing a context for how EAT has helped shape our understanding of self tolerance and autoimmunity.

Cross-feeding modulates antibiotic tolerance in bacterial communities.

Microbes frequently rely on metabolites excreted by other bacterial species, but little is known about how this cross-feeding influences the effect of antibiotics. We hypothesized that when species rely on each other for essential metabolites, the minimum inhibitory concentration (MIC) for all species will drop to that of the "weakest link"-the species least resistant in monoculture. We tested this hypothesis in an obligate cross-feeding system that was engineered between Escherichia coli, Salmonella enterica, and Methylobacterium extorquens. The effect of tetracycline and ampicillin were tested on both liquid and solid media. In all cases, resistant species were inhibited at significantly lower antibiotic concentrations in the cross-feeding community than in monoculture or a competitive community. However, deviation from the "weakest link" hypothesis was also observed in cross-feeding communities apparently as result of changes in the timing of growth and cross-protection. Comparable results were also observed in a clinically relevant system involving facultative cross-feeding between Pseudomonas aeruginosa and an anaerobic consortium found in the lungs of cystic fibrosis patients. P. aeruginosa was inhibited by lower concentrations of ampicillin when cross-feeding than when grown in isolation. These results suggest that cross-feeding significantly alters tolerance to antibiotics in a variety of systems.