The location of Helicobacter pylori in the gastric mucosa of mammals is defined by natural pH gradients within the gastric mucus, which are more alkaline proximal to the mucosal epithelial cells and more acidic toward the lumen. We have used a microscope slide-based pH gradient assay and video data collection system to document pH-tactic behavior. In response to hydrochloric acid (HCl), H. pylori changes its swimming pattern from straight-line random swimming to arcing or circular patterns that move the motile population away from the strong acid. Bacteria in more-alkaline regions did not swim toward the acid, suggesting the pH taxis is a form of negative chemotaxis. To identify the chemoreceptor(s) responsible for the transduction of pH-tactic signals, a vector-free allelic replacement strategy was used to construct mutations in each of the four annotated chemoreceptor genes (tlpA, tlpB, tlpC, and tlpD) in H. pylori strain SS1 and a motile variant of strain KE26695. All deletion mutants were motile and displayed normal chemotaxis in brucella soft agar, but only tlpB mutants were defective for pH taxis. tlpD mutants exhibited more tumbling and arcing swimming, while tlpC mutants were hypermotile and responsive to acid. While tlpA, tlpC, and tlpD mutants colonized mice to near wild-type levels, tlpB mutants were defective for colonization of highly permissive C57BL/6 interleukin-12 (IL-12) (p40 ؊/؊ )-deficient mice. Complementation of the tlpB mutant (tlpB expressed from the rdxA locus) restored pH taxis and infectivity for mice. pH taxis, like motility and urease activity, is essential for colonization and persistence in the gastric mucosa, and thus TlpB function might represent a novel target in the development of therapeutics that blind tactic behavior.Helicobacter pylori is a highly motile, urease-positive, gramnegative pathogen that establishes lifelong infections of the gastric mucosa of much of the world's population (8,29,35). These bacteria live deep in the mucus layer, near the underlying epithelial cells and away from the highly acidic lumen. H. pylori must also survive direct exposure to stomach acid during the initial colonization process or perhaps during repopulation following failed eradication therapy. Mutational studies have established both motility and functional urease activity as essential for colonization in animal models of infection (4,14,26,38). Infections with H. pylori tend to be antral predominant, but little is known regarding how bacteria ultimately select the site for colonization. It has been suggested that gastric acidity dictates the site of colonization (1, 17, 34), and in areas of endemicity, constant ingestion of bacteria, particularly by young children, exposes all areas of the stomach to colonization, allowing infections to predominate in the more permissive regions such as the less acidic antrum.Most H. pylori bacteria are located deep within the gastric mucus layer, being distributed within ϳ30 m of the mucosal epithelial cells, and on histology can be observed within the...

The Carba NP test was evaluated against a panel of 244 carbapenemase- and non-carbapenemase-producing Enterobacteriaceae and Pseudomonas aeruginosa isolates. We confirmed the 100% specificity and positive predictive value of the test, but the sensitivity and negative predictive value were 72.5% and 69.2%, respectively, and increased to 80% and 77.3%, respectively, using a more concentrated bacterial extract. False-negative results were associated with mucoid strains or linked to enzymes with low carbapenemase activity, particularly OXA-48-like, which has emerged globally in enterobacteria.

The rate of clinical failure following treatment of N. gonorrhoeae infections with cefixime was relatively high at a Toronto clinic and was associated with elevated MICs.

bResistance to rifampin (RIF) and rifabutin (RFB) in Mycobacterium tuberculosis is associated with mutations within an 81-bp region of the rpoB gene (RIF resistance-determining region [RRDR]). Previous studies have shown that certain mutations in this region are more likely to confer high levels of RIF resistance, while others may be found in phenotypically susceptible isolates. In this study, we sought to determine the relationship between the MICs of RIF and RFB and rpoB RRDR mutations in 32 multidrug-resistant (MDR), 4 RIF-monoresistant, and 5 susceptible M. tuberculosis clinical isolates. The MICs were determined using the MGIT 960 system. Mutations in the rpoB RRDR were determined by Sanger sequencing. RpoB proteins with mutations S531L (a change of S to L at position 531), S531W, H526Y, and H526D and the double mutation D516A-R529Q were associated with high MICs for RIF and RFB. Five isolates carrying the mutations L511P, H526L, H526N, and D516G-S522L were found to be susceptible to RIF. Several mutations were associated with resistance to RIF and susceptibility to RFB (F514FF, D516V, and S522L). Whole-genome sequencing of two MDR isolates without rpoB RRDR mutations revealed a mutation outside the RRDR (V146F; RIF MIC of 50 g/ml). The implications of the polymorphisms identified in the second of these isolates in RIF resistance need to be further explored. Our study further establishes a correlation between the mutations and the MICs of RIF and, also, RFB in M. tuberculosis. Several rpoB mutations were identified in RIF-and RFB-susceptible isolates. The clinical significance of these findings requires further exploration. Until then, a combination of phenotypic and molecular testing is advisable for drug susceptibility testing.