Usefulness of Leifson staining method in diagnosis of Helicobacter pylori infection

Halomonas gemina sp. nov. and Halomonas llamarensis sp. nov., two siderophore-producing organisms isolated from high-altitude salars of the Atacama Desert

Introduction

This study aimed to identify and characterize novel siderophore-producing organisms capable of secreting high quantities of the iron-binding compounds. In the course of this, two not yet reported halophilic strains designated ATCHA^T and ATCH28^T were isolated from hypersaline, alkaline surface waters of Salar de Llamará and Laguna Lejía, respectively. The alkaline environment limits iron bioavailability, suggesting that native organisms produce abundant siderophores to sequester iron.

Methods

Both strains were characterized by polyphasic approach. Comparative analysis of the 16S rRNA gene sequences revealed their affiliation with the genus Halomonas. ATCHA^T showed close similarity to Halomonas salicampi and Halomonas vilamensis, while ATCH28^T was related closest to Halomonas ventosae and Halomonas salina. The ability of both strains to secrete siderophores was initially assessed using the chromeazurol S (CAS) liquid assay and subsequently further investigated through genomic analysis and NMR. Furthermore, the effect of various media components on the siderophore secretion by strain ATCH28^T was explored.

Results

The CAS assay confirmed the ability of both strains to produce iron-binding compounds. Genomic analysis of strain ATCHA^T revealed the presence of a not yet reported NRPS-dependant gene cluster responsible for the secretion of siderophore. However, as only small amounts of siderophore were secreted, further investigations did not lie within the scope of this study. Via NMR and genomic analysis, strain ATCH28^T has been determined to produce desferrioxamine E (DFOE). Although this siderophore is common in various terrestrial microorganisms, it has not yet been reported to occur within Halomonas, making strain ATCH28^T the first member of the genus to produce a non-amphiphilic siderophore. By means of media optimization, the produced quantity of DFOE could be increased to more than 1000 µM.

Discussion

Phenotypic and genotypic characteristics clearly differentiated both strains from other members of the genus Halomonas. Average nucleotide identity (ANI) values and DNA-DNA relatedness indicated that the strains represented two novel species. Therefore, both species should be added as new representatives of the genus Halomonas, for which the designations Halomonas llamarensis sp. nov. (type strain ATCHA^T = DSM 114476 = LMG 32709) and Halomonas gemina sp. nov. (type strain ATCH28^T = DSM 114418 = LMG 32708) are proposed.

Detection of Helicobacter pylori infection in symptomatic Bulgarian adults

This study assessed the prevalence of Helicobacter pylori in symptomatic Bulgarian adults by means of culture, Gram's stain and an in-house rapid urease test (RUT), and also assessed the H. pylori density by culture. In total, 1441 non-treated and 270 treated patients were evaluated. Most non-treated patients with ulcers (87.7%), gastric malignancy (79.2%) and other gastroduodenal diseases (73.4%) were H. pylori-positive. Among non-treated and treated patients, 75.3% and 54.8%, respectively, of elderly patients, and 78.3% and 56.1%, respectively, of other adults were H. pylori-positive. Two (0.1%) non-treated adults were Helicobacter heilmannii-positive. The accuracy of direct Gram's stain and the in-house RUT were 74.8% and 64.2% in non-treated patients, and 73.7% and 63.0% in treated patients, respectively. Culture was highly accurate (>95%) in both groups. Older age decreased the sensitivity of the RUT in non-treated patients by 10.7% and that of all tests in treated patients by 6.9-8.1%. Incubation for 11 days was required for the growth of 2% and 4% of the strains from treated patients on selective and non-selective medium, respectively. There were no differences in isolation rates between positive fresh (74.2%) and frozen (75.2%) specimens. In non-treated adults, a high H. pylori density (growth in all quadrants of the plates) was more common (43.1%) in ulcer patients than in other patients (25.4%). In conclusion, H. pylori infection was common in Bulgarian patients, and at a high density in >40% of ulcer patients, while H. heilmannii infection was uncommon. Culture provided a highly accurate diagnostic approach. Stomach biopsies from non-treated patients can be frozen for several days. The benefit of reporting H. pylori density, as determined by culture, requires further evaluation.