Spatial and Temporal Shifts in Bacterial Biogeography and Gland Occupation during the Development of a Chronic Infection

Abstract

Gland colonization may be one crucial route for bacteria to maintain chronic gastrointestinal infection. We developed a quantitative gland isolation method to allow robust bacterial population analysis and applied it to the gastric pathobiont Helicobacter pylori. After infections in the murine model system, H. pylori populations multiply both inside and outside glands in a manner that requires the bacteria to be motile and chemotactic. H. pylori is able to achieve gland densities averaging 25 to 40 bacteria/gland after 2 to 4 weeks of infection. After 2 to 4 weeks of infection, a primary infection leads to colonization resistance for a secondary infection. Nonetheless, about ~50% of the glands remained unoccupied, suggesting there are as-yet unappreciated parameters that prevent gastric gland colonization. During chronic infections, H. pylori populations collapsed to nearly exclusive gland localization, to an average of <8 bacteria/gland, and only 10% of glands occupied. We analyzed an H. pylori chemotaxis mutant (Che−) to gain mechanistic insight into gland colonization. Che− strains had a severe inability to spread to new glands and did not protect from a secondary infection but nonetheless achieved a chronic gland colonization state numerically similar to that of the wild type. Overall, our analysis shows that bacteria undergo substantial population dynamics on the route to chronic colonization, that bacterial gland populations are maintained at a low level during chronic infection, and that established gland populations inhibit subsequent colonization. Understanding the parameters that promote chronic colonization will allow the future successful design of beneficial microbial therapeutics that are able to maintain long-term mammalian colonization.

Chemotaxis allows bacteria to overcome host-generated reactive oxygen species that constrain gland colonization

“…We next sought to examine TlpD’s role in gland colonization. To monitor gland colonization, we employed the bacterial localization in isolated glands (BLIG) approach in which gastric glands are isolated from the infected corpus or antrum tissue, epithelial cells labeled with Hoechst DNA stain, and glands examined for the presence of GFP+ H. pylori by fluorescent microscopy (5). Bacteria within glands were counted manually, and two parameters of gland colonization were compared between H. pylori strains.…”

“…Bacteria too appear to have special adaptations to the gland niche. These include the ability to use certain carbohydrates (4) and perform chemotaxis (5–7). The chronically-colonizing gastric pathogen Helicobacter pylori is one such microbe that requires chemotaxis for gland colonization (5–7).…”

“…These include the ability to use certain carbohydrates (4) and perform chemotaxis (5–7). The chronically-colonizing gastric pathogen Helicobacter pylori is one such microbe that requires chemotaxis for gland colonization (5–7). Chemotaxis permits bacteria to sample their environment via chemoreceptors that use ligand-binding signals to alter the autophosphorylation of a complexed histidine kinase CheA.…”

Helicobacter pylori Senses Bleach as a Chemoattractant Using a Cytosolic Chemoreceptor

“…Neutrophils concentrate near the stem precursor and cell zones of the gastric gland epithelium (Lee, 2014) which undergoes proliferation in response to H. pylori gastric gland colonization (Sigal et al, 2015). H. pylori colonization of the gastric glands is an important strategy for the bacteria’s persistent infection of the stomach and requires chemotaxis (Howitt et al, 2011; Keilberg et al, 2016), and therefore chemoattraction to HOCl may constitute a strategy H. pylori uses to persist in neutrophil-infiltrated gastric glands.…”

The Helicobacter pylori biofilm involves a multi-gene stress-biased response including a structural role for flagella

“…H. pylori colonizes gastric epithelial surfaces and within the thin layer of mucus near the cells (3). More recently, H. pylori was found to colonize within gastric glands, repeated invaginations of the gastrointestinal tract, which may provide the bacteria a favorable niche (4,5). Even though most infections are asymptomatic, H. pylori persistence is considered a major risk factor for gastric and duodenal ulcers, gastric Mucosa-Associated Lymphoid Tissue (MALT) lymphoma, and gastric adenocarcinoma (6).…”