| 1. |
- Abdulkarim, Farhad, et al.
(författare)
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Homologous recombination between the tuf genes of Salmonella typhimurium
- 1996
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Ingår i: Journal of Molecular Biology. - : Elsevier BV. - 0022-2836 .- 1089-8638. ; 260:4, s. 506-522
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Tidskriftsartikel (refereegranskat)abstract
- The genes coding for the translation factor EF-Tu, tufA and tufB are separated by over 700 kb on the circular chromosome of Salmonella typhimurium. The coding regions of these genes have 99% identity at the nucleotide level in spite of the presumed ancient origin of the gene duplication. Sequence comparisons between S. typhimurium and Escherichiacoli suggest that within each species the two tuf genes are evolving inconcert. Here we show that each of the S. typhimurium tuf genes cantransfer genetic information to the other. In our genetic system thetransfers are seen as non-reciprocal, i.e. as gene conversion events.However, the mechanism of recombination could be reciprocal, with sisterchromosome segregation and selection leading to the isolation of aparticular class of recombinant. The amount of sequence informationtransferred in individual recombination events varies, but can be close tothe entire length of the gene. The recombination is RecABCD-dependent,and is opposed by MutSHLU mismatch repair. In the wild-type, this typeof recombination occurs at a rate that is two or three orders of magnitudegreater than the nucleotide substitution rate. The rate of recombinationdiffers by six orders of magnitude between a recA and a mutS strain.Mismatch repair reduces the rate of this recombination 1000-fold. The rateof recombination also differs by one order of magnitude depending onwhich tuf gene is donating the sequence selected for. We discuss threeclasses of model that could, in principle, account for the sequencetransfers: (1) tuf mRNA mediated recombination; (2) non-allelic reciprocalrecombination involving sister chromosomes; (3) non-allelic geneconversion involving sister chromosomes, initiated by a double-strandbreak close to one tuf gene. Although the mechanism remains to bedetermined, the effect on the bacterial cells is tuf gene sequencehomogenisation. This recombination phenomenon can account for theconcerted evolution of the tuf genes.
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| 2. |
- Abdulkarim, Farhad, et al.
(författare)
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Missense substitutions lethal to essential functions of EF-Tu
- 1991
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Ingår i: Biochimie. - : Elsevier BV. - 0300-9084 .- 1638-6183. ; 73:12, s. 1457-1464
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Tidskriftsartikel (refereegranskat)abstract
- We have used a simple selection and screening method to isolate function defective mutants of EF-Tu. From 28 mutants tested, 12 different missense substitutions, individually lethal to some essential function of EF-Tu, were identified by sequencing. In addition we found a new non-lethal missense mutation. The frequency of isolation of unique mutations suggests that this method can be used to easily isolate many more. The lethal mutations occur in all three structural domains of EF-Tu, but most are in domain II. We aim to use these mutants to define functional domains on EF-Tu.
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| 3. |
- Abdulkarim, Farhad, et al.
(författare)
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Mutations to kirromycin resistance occur in the interface of domains I and III of EF-Tu.GTP
- 1994
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Ingår i: FEBS Letters. - : Wiley. - 0014-5793 .- 1873-3468. ; 352, s. 118-122
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Tidskriftsartikel (refereegranskat)abstract
- The antibiotic kirromycin inhibits protein synthesis by binding to EF-Tu and preventing its release from the ribosome after GTP hydrolysis.We have isolated and sequenced a collection of kirromycin resistant tuf mutations and identified thirteen single amino acid substitutions at sevendifferent sites in EF-Tu. These have been mapped onto the 3D structures of EF-Tu’GTP and EF-Tu.GDP. In the active GTP form of EF-Tu themutations cluster on each side of the interface between domains I and III. We propose that this domain interface is the binding site for kirromycin.
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| 4. |
- Adlerberth, Ingegerd, 1959, et al.
(författare)
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A mannose-specific adherence mechanism in Lactobacillus plantarum conferring binding to the human colonic cell line HT-29.
- 1996
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Ingår i: Applied and environmental microbiology. - 0099-2240. ; 62:7, s. 2244-51
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Tidskriftsartikel (refereegranskat)abstract
- Two Lactobacillus plantarum strains of human intestinal origin, strains 299 (= DSM 6595) and 299v (= DSM 9843), have proved to be efficient colonizers of the human intestine under experimental conditions. These strains and 17 other L. plantarum strains were tested for the ability to adhere to cells of the human colonic cell line HT-29.L.plantarum 299 and 299v and nine other L. plantarum strains, including all six strains that belong to the same genetic subgroup as L. plantarum 299 and 299v, adhered to HT-29 cells in a manner that could be inhibited by methyl-alpha-D-mannoside. The ability to adhere to HT-29 cells correlated with an ability to agglutinate cells of Saccharomyces cerevisiae and erythrocytes in a mannose-sensitive manner and with adherence to D-mannose-coated agarose beads. L. plantarum 299 and 299v adhered to freshly isolated human colonic and ileal enterocytes, but the binding was not significantly inhibited by methyl-alpha-D-mannoside. Periodate treatment of HT-29 cells abolished mannose-sensitive adherence, confirming that the cell-bound receptor was of carbohydrate nature. Proteinase K treatment of the bacteria also abolished adherence, indicating that the binding involved protein structures on the bacterial cell surface. Thus, a mannose-specific adhesin has been identified in L. plantarum; this adhesin could be involved in the ability to colonize the intestine.
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| 5. |
- Adlerberth, Ingegerd, 1959, et al.
(författare)
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Adhesins of Escherichia coli associated with extra-intestinal pathogenicity confer binding to colonic epithelial cells.
- 1995
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Ingår i: Microbial pathogenesis. - 0882-4010. ; 18:6, s. 373-85
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Tidskriftsartikel (refereegranskat)abstract
- Escherichia coli adhesins are virulence factors in intestinal and extra-intestinal infections, but their role in normal intestinal colonization has not been defined. We investigated the intestinal adherence of E. coli with Dr hemagglutinin, S fimbriae, CFA/I or CFA/II, using freshly isolated ileal or colonic enterocytes and cells from the human colonic cell line HT-29. E. coli with S-fimbrial adhesins (Sfa I or Sfa II), P or type 1 fimbriae, adhered in a non-polarized manner, and in similar numbers to colonic and ileal enterocytes. S fimbriae of the variety Sfa II (originating from a meningitis isolate), mediated a stronger binding than Sfa I (of uropathogenic origin). Strains expressing Dr hemagglutinin adhered preferentially to the brush borders, slightly better to colonic than ileal enterocytes. Strains expressing CFA/I or II adhered to colonic and ileal enterocytes, although brush border adherence was predominantly observed with ileal cells. Binding to HT-29 cells paralleled binding to colonic enterocytes for all adhesin specificities except CFA/I. The results suggest that Dr hemagglutinin, P-, type 1- and S-fimbrial adhesins mediate binding to both colonic and ileal enterocytes. These specificities may contribute to the establishment of E. coli in the intestinal microflora, which precedes their spread to extra-intestinal sites.
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| 6. |
- Adlerberth, Ingegerd, 1959, et al.
(författare)
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High turnover rate of Escherichia coli strains in the intestinal flora of infants in Pakistan.
- 1998
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Ingår i: Epidemiology and infection. - 0950-2688. ; 121:3, s. 587-98
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Tidskriftsartikel (refereegranskat)abstract
- The Escherichia coli flora of infants in developed countries is dominated by one or a few strains which persist for prolonged periods of time, but no longitudinal studies have been performed in developing countries. To this end, we studied the rectal enterobacterial flora in 22 home-delivered Pakistani infants during their first 6 months of life. Three colonies were isolated and species typed on each of 11 sampling occasions. E. coli isolates were strain typed using electromorphic typing of cytoplasmic enzymes, and their O serogroups were determined. There was a very rapid turnover of enterobacterial strains in the rectal flora of individual infants. On average, 8.5 different E. coli strains were found per infant, and several biotypes of other enterobacteria. Less than 50% of the infants were colonized with E. coli from their mothers, but strains of maternal origin were four times more likely to persists in the infants' flora than other E. coli strains. Enterobacteria other than E. coli were always of non-maternal origin, and Enterobacter cloacae and Klebsiella pneumoniae biotypes recovered from contaminated feeds were later identified in the infants' rectal flora. An early colonization with klebsiella or enterobacter was significantly associated with diarrhoea during the neonatal period, although these bacteria were not likely to be the cause of the disease. The results suggest that poor hygienic conditions result in an unstable and diverse enterobacterial flora, which may influence infant health.
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| 7. |
- Adlerberth, Ingegerd, 1959, et al.
(författare)
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Interaction of P-fimbriated Escherichia coli with human meconium.
- 1991
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Ingår i: FEMS microbiology letters. - 0378-1097. ; 68:1, s. 57-62
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Tidskriftsartikel (refereegranskat)abstract
- The ability of Escherichia coli with different receptor specificities to interact with meconium was studied. E. coli strains expressing P-fimbriae, specific for Gal alpha 1-4Gal beta-containing receptors, were agglutinated by meconium at high titres. This reaction was inhibited by globotetraosylceramide. The attachment of P-fimbriated E. coli to human colonic epithelial cells of the HT-29 cell line was inhibited by meconium. Some type 1 fimbriated strains were agglutinated by meconium, but the agglutination was rarely blocked by methyl alpha-D-mannoside. The attachment by type 1 fimbriated strains to HT-29 cells was reduced by meconium only in some cases. These results suggest that meconium interacts with the P-fimbriae of E. coli, in a way that may influence bacterial colonization of the neonatal intestine.
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| 8. |
- Adlerberth, Ingegerd, 1959, et al.
(författare)
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Intestinal colonization with Enterobacteriaceae in Pakistani and Swedish hospital-delivered infants.
- 1991
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Ingår i: Acta paediatrica Scandinavica. - 0001-656X. ; 80:6-7, s. 602-10
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Tidskriftsartikel (refereegranskat)abstract
- Rectal cultures from Swedish and Pakistani hospital-delivered newborn infants were analysed regarding the early acquisition of enterobacteria. Swedish infants were delivered vaginally, Pakistani infants were delivered either vaginally or by caesarean section. The Swedish infants were all breast-fed, whereas breastfeeding was incomplete and often started late among the Pakistani infants. Both groups of Pakistani infants were more rapidly colonized with enterobacteria than were the Swedish infants. Cultures from Swedish infants seldom yielded more than one kind of enterobacteria; E. coli and Klebsiella were most frequently isolated. E. coli dominated in both Pakistani groups, but especially caesarean section delivered infants were in addition often colonized with Proteus, Klebsiella, Enterobacter or Citrobacter species. Breastfeeding from the first day of life reduced colonization with Klebsiella/Enterobacter/Citrobacter. The results suggest that environmental exposure, delivery mode and early feeding habits all influence the early intestinal colonization with enterobacteria.
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| 9. |
- Adlerberth, Ingegerd, 1959, et al.
(författare)
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P fimbriae and other adhesins enhance intestinal persistence of Escherichia coli in early infancy.
- 1998
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Ingår i: Epidemiology and infection. - 0950-2688. ; 121:3, s. 599-608
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Tidskriftsartikel (refereegranskat)abstract
- Resident and transient Escherichia coli strains were identified in the rectal flora of 22 Pakistani infants followed from birth to 6 months of age. All strains were tested for O-antigen expression, adhesin specificity (P fimbriae, other mannose-resistant adhesins or type 1 fimbriae) and adherence to the colonic cell line HT-29. Resident strains displayed higher mannose-resistant adherence to HT-29 cells, and expressed P fimbriae (P = 0.0036) as well as other mannose-resistant adhesins (P = 0.012) more often than transient strains. In strains acquired during the first month of life, P fimbriae were 12 times more frequent in resident than in transient strains (P = 0.0006). The O-antigen distribution did not differ between resident and transient strains, and none of the resident P-fimbriated strains belonged to previously recognized uropathogenic clones. The results suggest that adhesins mediating adherence to intestinal epithelial cells, especially P fimbriae, enhance the persistence of E. coli in the large intestine of infants.
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| 10. |
- Agace, William
(författare)
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The role of the epithelial cell in Escherichia coli induced neutrophil migration into the urinary tract.
- 1996
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This study examined the molecular mechanisms of neutrophil migration to sites of mucosal bacterial infection. (1) Bacterial induction of neutrophil chemotactic cytokines and their role in neutrophil migration. Uropathogenic E.coli were shown to stimulate urinary tract epithelial cells to produce a specific array of cytokines including the neutrophil chemoattractant IL-8. IL-8 production was dependent on the adherence properties of the infecting strain. Deliberate colonisation of the human urinary tract with E.coli induced the local production of IL-8 and levels correlated with urinary neutrophil numbers. The E.coli induced IL-8 supported neutrophil migration across urinary tract epithelial layers in vitro and anti-IL-8 antibody blocked this response. The chemotactically active IL-8 was localised to the epithelial surface and these cells contained IL-8 receptor A and B mRNA. (2) The role of epithelial adhesion molecules in E.coli induced transuroepithelial migration. Uroepithelial cells constitutively expressed ICAM-1 and E.coli augmented ICAM-1 expression. Transuroepithelial neutrophil migration was dependent on epithelial ICAM-1 and neutrophil Mac-1 (CD11b/CD18) expression. Thus urinary tract epithelial cells provide two prerequisites for neutrophil migration to the mucosal lumen; neutrophil chemoattractants and cell adhesion molecules. (3) The role of bacterial fimbriae for the induction of inflammation in the urinary tract. Patients and mice infected with a type 1 positive P fimbriated uropathogenic E.coli clone O1:K1:H7 showed significantly higher inflammatory responses than type 1 negative O1:K1:H7 isolates. Insertion of an npt gene into fimH (encoding the type 1 fimbrial adhesin) of a type 1 positive O1:K1:H7 isolate resulted in the loss of the type 1 fimbrial phenotype and a reduction in virulence.
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