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Identification of Stenotrophomonas maltophilia genes that protect against phagocytosis using a high-throughput amoeba assay.

Stenotrophomonas maltophilia is a metabolically diverse species of Gram-negative bacteria found ubiquitously in soil and freshwater environments. Individual isolates may exist as free-living microorganisms, as members of the rhizosphere microbiota, as endophytes of plants, as endoparasites of amoeba, or as pathogens of vertebrates including fish, reptiles, and mammals. In humans, S. maltophilia is emerging as a significant cause for concern as an opportunistic pathogen associated with nosocomial outbreaks in patients with a range of comorbidities including cystic fibrosis, neutrophenia, chronic obstructive pulmonary disease, anti-cancer chemotherapy, and organ transplant. In most cases, S. maltophilia infection begins with colonization of an abiotic medical device and progresses to serious life-threating infection including pneumonia, neutropenic fever, meningitis, and blood stream infections. Based on data reported by the SENTRY Antimicrobial Surveillance Program, S. maltophilia is the 8th most prevalent Gram-negative pathogen (13th overall) recovered from patient samples in North America, yet we know almost nothing about the mechanisms of S. maltophilia pathogenesis. Our incomplete understanding of S. maltophilia is even more concerning when we consider that both the incidence and prevalence of this pathogen is on the rise. Resistance or evasion of host innate immunity is clearly important for progression of disease caused by S. maltophilia. Here, we report preliminary findings from a large-scale forward genetic screen designed to identify genes within the S. maltophilia genome that may be involved in resistance to phagocytosis. A large-insert (~40 kb) genomic library was screened for the ability to protect E. coli from predation by Dictyostelium discoideum, a bacterivorous environmental amoeba that shares structural and functional similarity with professional phagocytes of the innate immune system. Several positive clones were identified and transposon mutagenesis was used to further define S. maltophilia genes responsible for ectopic resistance to phagocytosis. This is an important first step in identification and characterization of virulence-associated genes in S. maltophilia.

Osama Mahdi and Nathan Fisher

Department of Veterinary and Microbiological Sciences, North Dakota State University

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Author:Mahdi, Osama; Fisher, Nathan
Publication:Proceedings of the North Dakota Academy of Science
Article Type:Author abstract
Date:Jan 1, 2014
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