The ulcer-causing pathogen Helicobacter pylori uses directed motility, or chemotaxis, to both colonize the stomach and promote disease development. Previous work showed that mutants lacking the TlpB chemoreceptor, one of the receptors predicted to drive chemotaxis, led to less inflammation in the gerbil stomach than did the wild type. Here we expanded these findings and examined the effects on inflammation of completely nonchemotactic mutants and mutants lacking each chemoreceptor. Of note, all mutants colonized mice to the same levels as did wild-type H. pylori. Infection by completely nonchemotactic mutants (cheW or cheY) resulted in significantly less inflammation after both 3 and 6 months of infection. Mutants lacking either the TlpA or TlpB H. pylori chemotaxis receptors also had alterations in inflammation severity, while mutants lacking either of the other two chemoreceptors (TlpC and HylB) behaved like the wild type. Fully nonchemotactic and chemoreceptor mutants adhered to cultured gastric epithelial cells and caused cellular release of the chemokine interleukin-8 in vitro similar to the release caused by the wild type. The situation appeared to be different in the stomach. Using silver-stained histological sections, we found that nonchemotactic cheY or cheW mutants were less likely than the wild type to be intimately associated with the cells of the gastric mucosa, although there was not a strict correlation between intimate association and inflammation. Because others have shown that in vivo adherence promotes inflammation, we propose a model in which H. pylori uses chemotaxis to guide it to a productive interaction with the stomach epithelium.

A comprehensive evaluation of every patient with a bloodstream infection includes an attempt to identify the infectious source. Pathogens can originate from various places, such as the gut microbiome, skin, and external environment. Identifying the definitive origin of an infection would enable precise interventions focused on management of the source 1 , 2 . Unfortunately, hospital infection control practices are often informed by assumptions about the source of various specific pathogens; if these assumptions are incorrect they lead to interventions that do not decrease pathogen exposure 3 . Here, we develop and apply a streamlined bioinformatic tool, named StrainSifter, to match bloodstream pathogens precisely to a candidate source. We then leverage this approach to interrogate the gut microbiome as a potential reservoir of bloodstream pathogens in a cohort of hematopoietic cell transplantation recipients. We find that patients with Escherichia coli and Klebsiella pneumoniae bloodstream infections have concomitant gut colonization with these organisms, suggesting that the gut may be a source of these infections. We also find cases where classically non-enteric pathogens, such as Pseudomonas aeruginosa and Staphylococcus epidermidis , are found in the gut microbiome, thereby challenging existing informal dogma of these infections originating from environmental or skin sources. Thus, we present an approach to distinguish the source of various bloodstream infections, which may facilitate more accurate tracking and prevention of hospital-acquired infections.

Cytoplasmic chemoreceptors are widespread among prokaryotes but are far less understood than transmembrane chemoreceptors, despite being implicated in many processes. One such cytoplasmic chemoreceptor is Helicobacter pylori TlpD, which is required for stomach colonization and drives a chemotaxis response to cellular energy levels. Neither the signals sensed by TlpD nor its molecular mechanisms of action are known. We report here that TlpD functions independently of the other chemoreceptors. When TlpD is the sole chemoreceptor, it is able to localize to the pole and recruits CheW, CheA, and at least two CheV proteins to this location. It loses the normal membrane association that appears to be driven by interactions with other chemoreceptors and with CheW, CheV1, and CheA. These results suggest that TlpD can form an autonomous signaling unit. We further determined that TlpD mediates a repellent chemotaxis response to conditions that promote oxidative stress, including being in the presence of iron, hydrogen peroxide, paraquat, and metronidazole. Last, we found that all tested H. pylori strains express TlpD, whereas other chemoreceptors were present to various degrees. Our data suggest a model in which TlpD coordinates a signaling complex that responds to oxidative stress and may allow H. pylori to avoid areas of the stomach with high concentrations of reactive oxygen species. IMPORTANCE Helicobacter pylori senses its environment with proteins called chemoreceptors. Chemoreceptors integrate this sensory information to affect flagellum-based motility in a process called chemotaxis. Chemotaxis is employed during infection and presumably aids H. pylori in encountering and colonizing preferred niches. A cytoplasmic chemoreceptor namedTlpD is particularly important in this process, and we report here that this chemoreceptor is able to operate independently of other chemoreceptors to organize a chemotaxis signaling complex and mediate a repellent response to oxidative stress conditions. H. pylori encounters and must cope with oxidative stress during infection due to oxygen and reactive oxygen species produced by host cells. TlpD's repellent response may allow the bacteria to escape niches experiencing inflammation and elevated reactive oxygen species (ROS) production. Chemoreceptors operate on the front line of the bacterial chemotaxis response, sensing signals and initiating attractant or repellent responses. Chemoreceptors can be divided into two classes based on whether they reside in the inner membrane or are soluble cytoplasmic proteins. The cytoplasmic class presumably senses signals that occur intracellularly. Cytoplasmic chemoreceptors are relatively understudied but represent 14% of bacterial and 43% of archaeal chemoreceptors (1). As a group, cytoplasmic chemoreceptors are reported to mediate tactic responses to diverse conditions, including to increased cellular energy stores (2, 3), redox conditions (4, 5), and metabolites (6), although significant gaps remain in our understanding of what they sense...

Helicobacter pylori must be motile or display chemotaxis to be able to fully infect mammals, but it is not known how this chemotaxis is directed. We disrupted two genes encoding predicted chemoreceptors, tlpA and tlpC. H. pylori mutants lacking either of these genes are fully motile and chemotactic in vitro and are as able as the wild type to infect mice when they are the sole infecting strains. In contrast, when mice are coinfected with the H. pylori SS1 tlpA or tlpC mutant and the wild type, we find more wild type than mutant after 2 weeks of colonization. Neither strain has an in vitro growth defect. These results suggest that the tlpA-and tlpCencoded proteins assist colonization of the stomach environment.

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