Pseudomonas aeruginosa is a versatile opportunistic pathogen that can cause devastating persistent infections. Complement is a highly conserved pathway of the innate immune system, and its role in the first line of defense against pathogens is widely appreciated. One of the earliest events in the complement cascade is the conversion of C3 to C3a and C3b, the latter typically binds to one or more acceptor molecules on the pathogen surface. We previously demonstrated that complement C3b binding acceptors exist on the P. aeruginosa surface. In the current study, we utilized either C3 polyclonal or C3b monoclonal antibodies in a farWestern technique followed by mass spectroscopy to identify the C3b acceptor molecule(s) on the P. aeruginosa surface. Our data provide evidence that OprF (an outer membrane porin, highly conserved in the Pseudomonadaceae) binds C3b. An oprFdeficient P. aeruginosa strain exhibits reduced C3 deposition compared to the wild type. We observed reduced internalization of oprF-deficient bacteria by neutrophils after opsonization compared with wild-type P. aeruginosa. Heterologous expression of OprF significantly enhanced C3b binding and increased serum-mediated bactericidal effects in complement-susceptible Escherichia coli. Furthermore, the predicted secondary structure of the C-terminal, surface-exposed region of OprF has high structural identity to the OmpA domain of several other Gram-negative bacteria, one of which is known to bind C3b. Therefore, these findings provide new insights into the biology of complement interactions with P. aeruginosa and other Gram-negative bacteria. Pseudomonas aeruginosa is an opportunistic nosocomial human pathogen that causes a wide range of clinical symptoms and infections in immunocompromised patients. This bacterium is often the causative agent of acute and chronic infections of the airway, sepsis, burn wounds, and skin infections. Excessive infiltration of neutrophils at the site of infection and the presence of complement have been observed in inflamed tissue and blood (1, 2). Serum sensitivity is directly dependent upon recognition of the bacterial surface by antibodies and complement (3). Prior studies also suggested that complement binds to the P. aeruginosa surface and enhances phagocytosis by acting as an opsonin (4). In this study, we sought to understand the consequences of complement interaction with P. aeruginosa. C3 is the central component of the complement system, playing a crucial role in the three major complement component activation processes. C3b, a product of C3 activation, binds covalently to bacterial surfaces through either a reactive intramolecular ester or an amide bond (5). C3b also participates in the formation of C5 convertase that cleaves C5 and initiates the sequential deposition of the remaining complement components to form the C5b-9 membrane attack complex (MAC), which may result in direct killing of microorganisms (6).The human complement system plays an important role in the clearance of early pulmonary P. aeruginosa inf...
In the United States, Clostridioides difficile infection (CDI) is the leading cause of healthcare-associated infection, affecting nearly half a million people and resulting in more than 20,000 in-hospital deaths every year. It is therefore imperative to better characterize the intricate interplay between C. difficile microbial factors, host immunologic signatures, and clinical features that are associated with adverse outcomes of severe CDI. In this narrative review, we discuss the implications of C. difficile genetics and virulence factors in the molecular epidemiology of CDI, and the utility of early biomarkers in predicting the clinical trajectory of patients at risk of developing severe CDI. Furthermore, we identify associations between host immune factors and CDI outcomes in both animal models and human studies. Next, we highlight clinical factors including renal dysfunction, aging, blood biomarkers, level of care, and chronic illnesses that can affect severe CDI diagnosis and outcome. Finally, we present our perspectives on two specific treatments pertinent to patient outcomes: metronidazole administration and surgery. Together, this review explores the various venues of CDI research and highlights the importance of integrating microbial, host, and clinical data to help clinicians make optimal treatment decisions based on accurate prediction of disease progression.
Background Exposure to certain medications, particularly antibiotics and proton pump inhibitors, has been associated with increased risk for Clostridium difficile infection (CDI). Studies have suggested an increased risk for CDI associated with exposure to certain non-steroidal anti-inflammatory drugs (NSAIDs). We conducted a retrospective case-control study to evaluate the risk for CDI associated with NSAID use. Methods The population included 1338 patients tested for CDI from February–December 2016 at the University of Michigan. NSAID use within 30 days of CDI testing was determined by chart review. Both scheduled and as-needed NSAID use met the definition for exposure, but aspirin use alone did not. Additional clinical data such as comorbid disease and baseline laboratory parameters were extracted through electronic query. A random forest model imputed missing data. A propensity score for NSAID use was developed via logistic regression and included gender, back pain, baseline serum creatinine, osteoarthritis, rheumatoid arthritis, serum albumin, and use of anticoagulant or antiplatelet medications. Cases were matched 1:1 with C. difficile negative controls by propensity score, with a matching caliper of 0.2 x standard deviation of the logit of the score. The final study population consisted of 1256 cases and their matched controls, however 6 cases could not be matched to controls as none had scores within the matching caliper. Conditional logistic regression was used to compare cases to controls. Results NSAID use was similar between the two groups on unadjusted analyses. The adjusted, multivariable model demonstrates that non-aspirin NSAID use is not a significant risk factor for CDI (P =.816), after adjustment for comorbid disease burden, age, and history of prior CDI (Table). Older age and prior CDI were independent risk factors for CDI (Table). Table Study population and modeling results Conclusion In this retrospective case-control study, non-aspirin NSAID use was not associated with an increased risk of CDI. To our knowledge, this is the first study of NSAID use as a risk factor for CDI that accounted for bias due to treatment assignment using a propensity score. Future studies should account for frequency or chronicity of NSAID use, which may affect the results. Disclosures Krishna Rao, MD, MS, Bio-K+ International, Inc. (Consultant)Merck and Co., Inc. (Research Grant or Support)Roche Molecular Systems, Inc. (Consultant)
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