Isolation and characterization of Azospirillum brasilense loci that correct Rhizobium meliloti exoB and exoC mutations.

The occurrence in Azospirillum brasilense of genes that code for exopolysaccharide (EPS) synthesis was investigated through complementation studies of Rhizobium meliloti Exo- mutants. These mutants are deficient in the synthesis of the major acidic EPS of Rhizobium species and form empty, non-nitrogen-fixing root nodules on alfalfa (J. A. Leigh, E. R. Signer, and G. C. Walker, Proc. Natl. Acad. Sci. USA 82:6231-6235, 1985). We demonstrated that the exoC mutation of R. meliloti could be corrected for EPS production by several cosmid clones of a clone bank of A. brasilense ATCC 29145. However, the EPS produced differed in structure from the wild-type R. meliloti EPS, and the symbiotic deficiency of the exoC mutation was not reversed by any of these cosmid clones. The exoB mutation could be corrected not only for EPS production but also for the ability to form nitrogen-fixing nodules on alfalfa by one particular cosmid clone of A. brasilense. Tn5 insertions in the cloned DNA were isolated and used to construct Azospirillum mutants with mutations in the corresponding loci by marker exchange. It was found that these mutants failed to produce the wild-type high-molecular-weight EPS, but instead produced EPSs of lower molecular weight.

A reliable screening test for childhood celiac disease: fluorescent immunosorbent test for gliadin antibodies. A prospective multicenter study.

The diagnostic value of gliadin antibody determination using the fluorescent immunosorbent test was examined in a prospective multicenter study comprising 251 children with malabsorptive disorders. Antibodies to gliadin were found in all 72 patients (100%) with active celiac disease (29 children with celiac disease proved by challenge, 43 with probable celiac disease). All children up to the age of 7 years had antibodies in high titers. By contrast, 96 (84%) of 114 children with other malabsorptive disorders and a normal mucosa or with partial villous atrophy had no gliadin antibodies, 14 (12%) had a low titer, and only four (3.5%) showed moderate to high titers. Four children with gastrointestinal tract symptoms of cow milk intolerance and a flat mucosa also showed no antibodies. In 24 of 29 children (83%) with cystic fibrosis and six of seven children with Crohn disease (biopsies not performed in either group), no antibodies could be detected. The others had low or elevated titers. In 25 children with acute gastroenteritis (not biopsied) antibodies were not found at hospital admission nor six weeks later after reintroduction of gluten. The determination of antibodies to gliadin with the fluorescent immunosorbent test is a reliable screening test for childhood celiac disease. In our series there were no false negative results in children with untreated celiac disease. A positive gliadin antibody titer is not proof of celiac disease. In each child the diagnosis must be confirmed by small intestinal biopsy even if the gliadin antibody titer is high. The detection of high titers of cow milk antibodies in 27% of patients with celiac disease is of no value.