Little is known about factors which enable Salmonella serotypes to circulate within populations of livestock and domestic fowl. We have identified a DNA region which is present in Salmonella serotypes commonly isolated from livestock and domestic fowl (S. enterica subspecies I) but absent from reptile-associated Salmonella serotypes (S. bongori and S. enterica subspecies II to VII). This DNA region was cloned from Salmonella serotype Typhimurium and sequence analysis revealed the presence of a 6,105-bp open reading frame, designated shdA, whose product's deduced amino acid sequence displayed homology to that of AIDA-I from diarrheagenic Escherichia coli, MisL of serotype Typhimurium, and IcsA of Shigella flexneri. The shdA gene was located adjacent to xseA at 52 min, in a 30-kb DNA region which is not present in Escherichia coli K-12. A serotype Typhimurium shdA mutant was shed with the feces in reduced numbers and for a shorter period of time compared to its isogenic parent. A possible role for the shdA gene during the expansion in host range of S. enterica subspecies I to include warm-blooded vertebrates is discussed.Salmonella serotypes are a frequent constituent of the intestinal flora of poikilothermic animals. The percentage of apparently healthy, cold-blooded vertebrates which harbor Salmonella serotypes ranges from 74 to 94% (20,28,32,34,59), and these bacteria could thus be considered part of the normal intestinal flora (23,48). Salmonella serotypes are also commonly isolated from a fraction (usually Ͻ20%) of warmblooded animal hosts (15,31,49,54). Although chronic carriers, which appear healthy, are observed within the human population and among warm-blooded animals (22,27,35,40), Salmonella serotypes are commonly associated with illness in these hosts (55). Consequently Salmonella serotypes are regarded as pathogens rather than part of the normal intestinal flora of homeothermic animals.On the basis of multilocus enzyme electrophoresis and comparative sequence analysis of orthologous genes, two species, S. enterica and S. bongori, have been assigned to the genus Salmonella (18,46). S. enterica is further subdivided into seven subspecies designated with roman numerals (18, 44). While S. bongori and S. enterica subspecies II, IIIa, IIIb, IV, VI, and VII are mainly associated with cold-blooded vertebrates, members of S. enterica subspecies I are frequently isolated from avian and mammalian hosts (44). For instance, of the 90,201 Salmonella isolates collected between 1977 and 1992 by the German National Reference Center for Enteric Pathogens from humans and warm-blooded animals, 89,798 isolates (99.55%) belonged to S. enterica subspecies I (1). Currently it is not clear which virulence mechanisms are responsible for the apparent adaptation of S. enterica subspecies I to circulation within populations of warm-blooded animals.S. bongori or S. enterica subspecies II to VII are able to infect humans, colonize the intestine and cause disease (1). Human infections with serotypes of S. bongori and S. enterica su...

In Helicobacter pylori, the contribution of efflux proteins to antibiotic resistance is not well established. As translocases that act in parallel may have overlapping substrate specificities, the loss of function of one such translocase may be compensated for by that of another translocase with no effect on susceptibilities to antibiotics. The genome of H. pylori 26695 was assessed for the presence of putative translocases and outer membrane efflux or TolC-like proteins which could interact to form efflux systems involved in drug resistance. Twenty-seven translocases were identified, of which HP1184 was the sole representative of the multidrug and toxic compound extrusion family of translocases and which could thus have a unique substrate specificity. In addition, four TolC-like proteins (HP0605, HP0971, HP1327, and HP1489) were identified. Thus, it is feasible that inactivation of a TolC-like protein would affect the functions of multiple translocases. We aimed to determine whether efflux systems contribute to antimicrobial susceptibility by evaluation of the susceptibility profiles of an HP1184-knockout mutant, four mutants in which one of the four TolC homologs was inactivated, as well as a mutant in which both HP0605 and HP0971 were inactivated. The HP1184-and HP1489-knockout mutants both showed increased susceptibilities to ethidium bromide, while the HP0605-knockout mutant exhibited increased susceptibilities to novobiocin and sodium deoxycholate. The HP0605 and HP0971 doubleknockout mutant was also more susceptible to metronidazole, in addition to being susceptible to novobiocin and sodium deoxycholate. Thus, active efflux is an eminent means of resistance to antimicrobials in H. pylori and resembles the situation in other bacteria.

The human gastric pathogen Helicobacterpylori infects the human gastric mucus layer of approximately half of the world's population. Colonization with this bacterium results in superficial gastritis without clinical symptoms, but can progress into gastric or duodenal ulcers, gastric malignancies and mucosa-associated lymphoid tissue-lymphomas. Disease outcome is affected by a complex interplay between host, environmental and bacterial factors. Irrespective of disease outcome, the majority of H. pylori infected individuals remain colonized for life. Changing conditions in the human gastric mucosa may alter gene expression and/or result in the outgrowth of more fit H. pylori variants. As such, H. pylori is a highly flexible organism that is optimally adapted to its host. the heterogeneity in H. pylori populations make predictions on H. pylori-related pathogenesis difficult. In this review, we discuss host, environmental and bacterial factors that are important in disease progression. Moreover, H. pylori adaptive mechanisms, which allow its life-long survival and growth in the gastric mucosa are considered.

Diffusion of (precursors of) these nutrients from the gastric epithelial cells is essential for H. pylori growth in vitro. We hypothesize that in vivo, H. pylori favors colonization near the tight junctions, to gain maximal access to the nutrient(s) released by gastric epithelial cells.

The identification of methylated sites on bacterial genomic DNA would be a useful tool to study the major roles of DNA methylation in prokaryotes: distinction of self and nonself DNA, direction of post-replicative mismatch repair, control of DNA replication and cell cycle, and regulation of gene expression. Three types of methylated nucleobases are known: N6-methyladenine, 5-methylcytosine and N4-methylcytosine. The aim of this study was to develop a method to detect all three types of DNA methylation in complete genomic DNA. It was previously shown that N6-methyladenine and 5-methylcytosine in plasmid and viral DNA can be detected by intersequence trace comparison of methylated and unmethylated DNA. We extended this method to include N4-methylcytosine detection in both in vitro and in vivo methylated DNA. Furthermore, application of intersequence trace comparison was extended to bacterial genomic DNA. Finally, we present evidence that intrasequence comparison suffices to detect methylated sites in genomic DNA. In conclusion, we present a method to detect all three natural types of DNA methylation in bacterial genomic DNA. This provides the possibility to define the complete methylome of any prokaryote.

To study the effect of initial colonisation on Helicobacter pylori gene expression, altered H. pylori gene transcription during co-culture with human gastric epithelial cells was determined. Therefore, an insertion library of H. pylori with random chromosomal fusions to a promoterless cat gene was grown in the presence of HM02 gastric epithelial cells and varying levels of chloramphenicol. One H. pylori transformant was chloramphenicol-resistant in the presence, but chloramphenicol-susceptible in the absence of gastric epithelial HM02 cells. This transformant had the promoterless cat gene inserted into the HP0887 gene, which encodes the vacuolating cytotoxin VacA, an important virulence factor of H. pylori. Reverse transcriptase polymerase chain reaction on cDNA of this transformant confirmed vacA upregulation near HM02 cells. These results show the applicability of this technique to study H. pylori gene regulation in its natural environment.

H. pylori YlxH is essential for the assembly of flagella and hence for the motility of H. pylori.