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Balamuthia mandrillaris is responsible for hundreds of reported cases of amoebic encephalitis, the majority of which have been fatal. Despite being an exceptionally deadly pathogen, B. mandrillaris is understudied, leaving many open questions regarding epidemiology, diagnosis, and treatment. Due to the lack of effective drugs to fight B. mandrillaris infections, mortality rates remain high even for patients receiving intensive care. This report addresses the need for new treatment options through a drug repurposing screen to identify novel B. mandrillaris inhibitors. The most promising candidate identified was the quinoline antibiotic nitroxoline, which has a long history of safe use in humans. We show that nitroxoline kills B. mandrillaris at pharmacologically relevant concentrations and exhibits greater potency and selectivity than drugs commonly used in the current standard of care. The findings that we present demonstrate the potential of nitroxoline to be an important new tool in the treatment of life-threatening B. mandrillaris infections.

Stenotrophomonas maltophilia is a ubiquitous bacterium and an emerging nosocomial pathogen. This bacterium is resistant to many antibiotics, associated with a number of infections, and a significant health risk, especially for immunocompromised patients. Given that Caenorhabditis elegans shares many conserved genetic pathways and pathway components with higher organisms, the study of its interaction with bacterial pathogens has biomedical implications. S. maltophilia has been isolated in association with nematodes from grassland soils, and it is likely that C. elegans encounters this bacterium in nature. We found that a local S. maltophilia isolate, JCMS, is more virulent than the other S. maltophilia isolates (R551-3 and K279a) tested. JCMS virulence correlates with intestinal distension and bacterial accumulation and requires the bacteria to be alive. Many of the conserved innate immune pathways that serve to protect C. elegans from various pathogenic bacteria also play a role in combating S. maltophilia JCMS. However, S. maltophilia JCMS is virulent to normally pathogen-resistant DAF-2/16 insulin-like signaling pathway mutants. Furthermore, several insulin-like signaling effector genes were not significantly differentially expressed between S. maltophilia JCMS and avirulent bacteria (Escherichia coli OP50). Taken together, these findings suggest that S. maltophilia JCMS evades the pathogen resistance conferred by the loss of DAF-2/16 pathway components. In summary, we have discovered a novel host-pathogen interaction between C. elegans and S. maltophilia and established a new animal model with which to study the mode of action of this emerging nosocomial pathogen. Stenotrophomonas maltophilia, a Gram-negative bacillus previously classified as both Pseudomonas and Xanthomonas (1), is an emerging nosocomial pathogen. From 1993 to 2004, S. maltophilia was found to be among the 11 organisms most frequently recovered from intensive care unit (ICU) patients in U.S. hospitals (2). A more recent study of patients with S. maltophilia bacteremia revealed that most cases were related to hospital admission, with some being associated with health care, such as outpatient intravenous antibiotics, treatment in a long-term-care facility, or chemotherapy (3). That study also found that intubation and ICU stay at the time of S. maltophilia bacteremia were associated with mortality (3). This is likely correlated with the propensity of S. maltophilia to adhere to plastics and form biofilms (4) and the opportunistic infection of patients with preexisting illnesses. In fact, S. maltophilia is the predominant bacterium recovered from the respiratory tract of patients with cystic fibrosis (5) and enhances the pathogenesis of Crohn's disease and ulcerative colitis (6, 7). Additionally, S. maltophilia can cause nosocomial pneumonia (8) and is associated with a number of infections, such as meningitis and endocarditis (reviewed in reference 9). Thus, S. maltophilia is a significant and medically important human pathogen. Furthermore, c...

Commentary: Lower respiratory tract infections are a leading cause of death in hematopoietic cellular transplant recipients, but the microbiologic etiology of these infections is frequently unknown. The limits of current diagnostics preclude targeted antimicrobial treatments, resulting in excess morbidity and mortality. Metagenomic next-generation sequencing may enable precision diagnosis of respiratory infections in hematopoietic cellular transplant patients by simultaneously detecting microbial pathogens, transcriptional biomarkers of the host response, and the pulmonary microbiome. This approach may facilitate targeted antimicrobial prescription and provide a new method for distinguishing infectious and non-infectious post-transplant respiratory illness. ABSTRACT RATIONALE: Current microbiologic diagnostics often fail to identify the etiology of lower respiratory tract infections (LRTI) in hematopoietic cellular transplant recipients (HCT), which precludes the implementation of targeted therapies. OBJECTIVES: To address the need for improved LRTI diagnostics, we evaluated the utility of metagenomic next generation sequencing (mNGS) of bronchoalveolar lavage (BAL) to detect microbial pathogens in HCT patients with acute respiratory illnesses. METHODS: We enrolled 22 post-HCT adults ages 19-69 years with acute respiratory illnesses who underwent BAL at the University of Michigan between January 2012 and May 2013. mNGS was performed on BAL fluid to detect microbes and simultaneously assess the host transcriptional response. Results were compared against conventional microbiologic assays. MEASUREMENTS & MAIN RESULTS: mNGS demonstrated 100% sensitivity for detecting respiratory microbes (human metapneumovirus, respiratory syncytial virus, Stenotrophomonas maltophilia, human herpesvirus 6 and cytomegalovirus) when compared to standard testing.Previously unrecognized LRTI pathogens were identified in six patients for whom standard testing was negative (human coronavirus 229E, human rhinovirus A, Corynebacterium propinquum and Streptococcus mitis); findings were confirmed by independent PCR and 16S rRNA sequencing. Relative to patients without infection, patients with infection had increased expression of immunity related genes (p=0.022) and significantly lower diversity of their respiratory microbiome (p=0.017). CONCLUSIONS:Compared to conventional diagnostics, mNGS enhanced detection of pathogens in BAL fluid from HCT patients. Furthermore, our results suggest that combining unbiased microbial pathogen detection with assessment of host gene biomarkers of immune response may hold promise for enhancing the diagnosis of post-HCT respiratory infections. Abstract Word Count: 249