A Positively Selected fur-R88H Mutation Enhances Helicobacter pylori Fitness in a High-Salt Environment and Alters Fur-Dependent Regulation of Gene Expression.

Both Helicobacter pylori infection and a high-salt diet are risk factors for gastric cancer. We previously showed that a mutation in fur (encoding the ferric uptake regulator variant Fur-R88H) was positively selected in H. pylori strains isolated from experimentally infected Mongolian gerbils receiving a high-salt diet. In the present study, we report that continuous H. pylori growth in high-salt conditions in vitro also leads to positive selection of the fur-R88H mutation. Competition experiments with strains containing wild-type fur or fur-R88H, each labeled with unique nucleotide barcodes, showed that the fur-R88H mutation enhances H. pylori fitness under high-salt conditions but reduces H. pylori fitness under routine culture conditions. The fitness advantage of the fur-R88H mutant under high-salt conditions was abrogated by the addition of supplemental iron. To test the hypothesis that the fur-R88H mutation alters the regulatory properties of Fur, we compared the transcriptional profiles of strains containing wild-type fur or fur-R88H. Increased transcript levels of fecA2, which encodes a predicted TonB-dependent outer membrane transporter, were detected in the fur-R88H variant compared to those in the strain containing wild-type fur under both high-salt and routine conditions. Competition experiments showed that fecA2 contributes to H. pylori fitness under both high-salt and routine conditions. These results provide new insights into mechanisms by which the fur-R88H mutation confers a selective advantage to H. pylori in high-salt environments.

Magnetic Extraction of Acinetobacter baumannii Using Colistin-Functionalized γ-Fe2O3/Au Core/Shell Composite Nanoclusters.

Acinetobacter baumannii is a Gram-negative bacterium of increasing concern due to its virulence and persistence in combat and healthcare environments. The incidence of both community-acquired and nosocomial A. baumannii infections is on the rise in foreign and domestic healthcare facilities. Treatment options are limited due to the acquisition of multidrug resistance to the few effective antibiotics. Currently, the most effective pharmaceutically based treatment for multidrug-resistant A. baumannii infections is the antibiotic colistin (polymyxin E). To minimize side effects associated with administration of colistin or other toxic antimicrobial agents, we propose the development of a nanotechnology-mediated treatment strategy. In this design-based effort, colistin-functionalized multilayered, inorganic, magnetoplasmonic nanoconstructs were fabricated to bind to the surface of A. baumannii. This result, for the first time, demonstrates a robust, pharmaceutical-based motif for high affinity, composite nanoparticulates targeting the A. baumannii surface. The antibiotic-activated nanomaterials demonstrated cytocompatibility with human cells and no acute bacterial toxicity at nanoparticle to bacterial concentrations <10 000:1. The magnetomotive characteristics of the nanomaterial enabled magnetic extraction of the bacteria. In a macroscale environment, maximal separation efficiencies exceeding 38% were achieved. This result demonstrates the potential for implementation of this technology into micro- or mesofluidic-based separation environments to enhance extraction efficiencies. The future development of such a mesofluidic-based, nanotechnology-mediated platform is potentially suitable for adjuvant therapies to assist in the treatment of sepsis.