GC content of DNA of Campylobacter pylori and other species belonging or related to the genus Campylobacter

Bacteriology and taxonomy of Helicobacter pylori

As the scientific community approaches the twentieth anniversary of the first isolation of H. pylori, it appears that despite the wealth of articles published in journals throughout the world every month, there are still many unanswered questions about the microbiology of this bacterium and others in the genus Helicobacter.

Helicobacter pylori

Helicobacter pylori is a gram-negative bacterium which causes chronic gastritis and plays important roles in peptic ulcer disease, gastric carcinoma, and gastric lymphoma. H. pylori has been found in the stomachs of humans in all parts of the world. In developing countries, 70 to 90% of the population carries H. pylori. In developed countries, the prevalence of infection is lower. There appears to be no substantial reservoir of H. pylori aside from the human stomach. Transmission can occur by iatrogenic, fecal-oral, and oral-oral routes. H. pylori is able to colonize and persist in a unique biological niche within the gastric lumen. All fresh isolates of H. pylori express significant urease activity, which appears essential to the survival and pathogenesis of the bacterium. A variety of tests to diagnose H. pylori infection are now available. Histological examination of gastric tissue, culture, rapid urease testing, DNA probes, and PCR analysis, when used to test gastric tissue, all require endoscopy. In contrast, breath tests, serology, gastric juice PCR, and urinary excretion of [15N]ammonia are noninvasive tests that do not require endoscopy. In this review, we highlight advances in the detection of the presence of the organism and methods of differentiating among types of H. pylori, and we provide a background for appropriate chemotherapy of the infection.

Helicobacter pylori

Helicobacter pylori is a gram-negative bacterium which causes chronic gastritis and plays important roles in peptic ulcer disease, gastric carcinoma, and gastric lymphoma. H. pylori has been found in the stomachs of humans in all parts of the world. In developing countries, 70 to 90% of the population carries H. pylori. In developed countries, the prevalence of infection is lower. There appears to be no substantial reservoir of H. pylori aside from the human stomach. Transmission can occur by iatrogenic, fecal-oral, and oral-oral routes. H. pylori is able to colonize and persist in a unique biological niche within the gastric lumen. All fresh isolates of H. pylori express significant urease activity, which appears essential to the survival and pathogenesis of the bacterium. A variety of tests to diagnose H. pylori infection are now available. Histological examination of gastric tissue, culture, rapid urease testing, DNA probes, and PCR analysis, when used to test gastric tissue, all require endoscopy. In contrast, breath tests, serology, gastric juice PCR, and urinary excretion of [15N]ammonia are noninvasive tests that do not require endoscopy. In this review, we highlight advances in the detection of the presence of the organism and methods of differentiating among types of H. pylori, and we provide a background for appropriate chemotherapy of the infection.

Nucleotide sequence of the gyrA gene and characterization of ciprofloxacin-resistant mutants of Helicobacter pylori

PCR was used to amplify a 238-bp region from Helicobacter pylori which corresponded to the quinolone resistance-determining region in Escherichia coli. The gyrA gene of H. pylori was cloned and sequenced. An open reading frame of 2,478 nucleotides coded for a polypeptide of 826 amino acids with a calculated molecular mass of 92,508 Da. The amino acid sequence showed an overall 52% identity with other bacterial gyrA genes but was most closely related to the gyrA subunit of Campylobacter jejuni (76.5% identity). Sequencing of the amplification product from ciprofloxacin-resistant mutants of H. pylori revealed four classes of mutations with substitutions at amino acid 87 (Asn-->Lys), amino acid 88 (Ala-->Val), and amino acid 91 (Asp-->Gly, -->Asn, or -->Tyr) and a double substitution at amino acids 91 and 97 (Ala-->Val). Ciprofloxacin-susceptible strains of H. pylori could be transformed to ciprofloxacin resistance by using the amplified fragment from resistant strains as donor DNA. Of the 11 ciprofloxacin-resistant mutants examined, only one did not have an alteration within the quinolone resistance-determining region, suggesting that, in H. pylori, resistance to quinolones is primarily a result of alterations in gyrA.

Molecular characterization of a conserved 20-kilodalton membrane-associated lipoprotein antigen of Helicobacter pylori

Antisera raised in rabbits to whole cells of Helicobacter pylori recognized as a major antigen a protein with an apparent molecular weight of 20,000. The antigen was purified by differential solubilization with N-octyl-beta-D-glucopyranoside, urea, and sodium dodecyl sulfate followed by molecular sieving. The mass of the protein, Lpp20, was 18,283 Da as determined by mass spectrometry. The lpp20 gene encoding this protein was cloned in Escherichia coli by using the vector lambda EMBL3, and plasmid subclones expressed the full-length protein from the native H. pylori promoter. lpp20 was mapped to the same 358-kb NruI fragment as flaB. DNA sequence analysis showed that the gene was 525 bp long and encoded a 175-amino-acid protein with a molecular weight of 19,094 containing a 21-residue typical lipoprotein signal peptide and consensus prolipoprotein processing site. The mass of the deduced 154-residue mature protein was 16,865 Da. Growth of E. coli cells expressing the cloned H. pylori lpp20 gene in the presence of [3H]palmitic acid resulted in radiolabelled Lpp20 while treatment of the E. coli cells with globomycin caused accumulation of unprocessed Lpp20, consistent with Lpp20 being a lipoprotein. Lpp20 cofractionated with the cytoplasmic membrane fraction, although a proportion of the protein was also found in the outer membrane. A mutant generated by mutant-allele exchange displayed normal viability, showing that Lpp20 belonged to the nonessential class of lipoproteins.

Purification of Helicobacter pylori superoxide dismutase and cloning and sequencing of the gene

The superoxide dismutase (SOD) of Helicobacter pylori, a pathogenic bacterium which colonizes the gastric mucosa, evoking a marked inflammatory response, was purified and characterized, and the N-terminal amino acid sequence was determined. The enzyme consists of two identical subunits each with an apparent molecular weight of 24,000. Analysis of the primary structure and inhibition studies revealed that H. pylori possesses a typical procaryotic iron-containing enzyme. No other isoenzymes could be detected. Indirect gold immunostaining of H. pylori SOD with a polyclonal antibody directed against the iron-containing SOD of Escherichia coli showed a surface-associated localization of the enzyme. The H. pylori SOD gene was cloned by functional complementation of a SOD-deficient E. coli mutant. Sequencing and alignment revealed striking homology to the following facultative intracellular human pathogens: Listeria ivanovii, Listeria monocytogenes, Coxiella burnetti, Porphyromonas gingivalis, Legionella pneumophila, and Entamoeba histolytica. An open reading frame of 642 bp encoding 214 amino acids was determined. There was no leader sequence detectable. Cloning of the H. pylori SOD gene is one of the prerequisites to investigation of its pathophysiological role in the defense against antimicrobial mechanisms of polymorphonuclear granulocytes.

Diversity among clinical isolates of Histoplasma capsulatum detected by polymerase chain reaction with arbitrary primers

Clinical isolates of the fungal respiratory and systemic pathogen Histoplasma capsulatum have been placed in several different classes by using genomic restriction fragment length polymorphisms (RFLPs), but in general have not been distinguished further. We report here that a polymerase chain reaction (PCR)-based DNA fingerprinting method that has been termed arbitrary primer or random amplified polymorphic DNA (RAPD) PCR can distinguish among isolates in a single RFLP class. In this method, arbitrarily chosen oligonucleotides are used to prime DNA synthesis from genomic sites that they fortuitously match, or almost match, to generate strain-specific arrays of DNA fragments. Each of 29 isolates of RFLP class 2, the group endemic in the American Midwest, was distinguished by using just three arbitrary primers. In contrast, laboratory-derived S and E colony morphology variants of two strains were not distinguished from their R parents by using 18 such primers. Thus, the clinical isolates of H. capsulatum are quite diverse, but their genomes remain stable during laboratory culture. These outcomes suggest new possibilities for epidemiological analysis and studies of fungal populations in infected hosts.

DNA diversity among clinical isolates of Helicobacter pylori detected by PCR-based RAPD fingerprinting

The RAPD (or AP-PCR) DNA fingerprinting method was used to distinguish among clinical isolates of Helicobacter pylori, a bacterium whose long term carriage is associated with gastritis, peptic ulcers and gastric carcinomas. This method uses arbitrarily chosen oligonucleotides to prime DNA synthesis from genomic sites to which they are fortuitously matched, or almost matched. Most 10-nt primers with > or = 60% G + C yielded strain-specific arrays of up to 15 prominent fragments, as did most longer (> or = 17-nt) primers, whereas most 10-nt primers with 50% G+C did not. Each of 64 independent H. pylori isolates, 60 of which were from patients in the same hospital, was distinguishable with a single RAPD primer, which suggests a high level of DNA sequence diversity within this species. In contrast, isolates from initial and followup biopsies were indistinguishable in each of three cases tested.

Use of DNA restriction endonuclease digest and ribosomal RNA gene probe patterns to fingerprint Helicobacter pylori and Helicobacter mustelae isolated from human and animal hosts

Variation amongst strains of Helicobacter pylori and Helicobacter mustelae was examined by DNA restriction endonuclease digestion and rRNA gene patterns generated using a non-radioactive probe. Chromosomal DNA was extracted from 30 cultures of H. pylori from human, Rhesus monkey and pig gastric mucosa, and from three H. mustelae isolates from ferret gastric mucosa. DNA fingerprinting with Hae III and Hind III showed H. mustelae was relatively homogeneous but revealed genomic heterogeneity within H. pylori with at least 18 different DNA patterns identifiable amongst the 30 isolates. Five sets of strains other than duplicates with matching DNA fingerprints were identified within H. pylori. The Peruvian isolates were the largest identical set and comprised eight isolates from four different patients with five consecutive isolates from one patient. The Rhesus monkey strains were a relatively homogeneous set as were several Australian human isolates. The study demonstrates that rRNA gene restriction patterns provide a simple but highly discriminatory electrophoretic fingerprint for H. pylori with potential for use as a novel epidemiological marker in addition to total DNA digest analysis.

Microbiological aspects of Helicobacter pylori (Campylobacter pylori)

The human gastric pathogen Campylobacter pylori has recently been reclassified as Helicobacter pylori, and a related spiral bacterium found in the stomach of ferrets has been designated Helicobacter mustelae. The general microbiological features of Helicobacter pylori are delineated here, with details of phenotypic differences between Helicobacter pylori and Helicobacter mustelae; comparisons are made with Wolinella succinogenes and Campylobacter jejuni. The Helicobacter organisms possess an external glycocalyx which can be visualised by electron microscopy, and which may be involved in bacterial adherence. The finding of soluble and cell-associated haemagglutinins of Helicobacter pylori is reported. Detection of Helicobacter pylori in clinical specimens, susceptibility of the organism to antibacterial agents, and other aspects of practical and clinical significance are briefly reviewed.