Intestinal immunoglobulin a response to naturally acquired enterotoxigenic Escherichia coli in US travelers to an endemic area of Mexico.

BACKGROUND: Simple methods for detecting secretory immunoglobulin A (sIgA) immune responses following natural enteric infection and oral immunization are needed. METHODS: Fourteen students from the United States acquiring enterotoxigenic Escherichia coli (ETEC) diarrhea in Mexico were studied for fecal immunoglobulin A (IgA) response to their homologous infecting ETEC and to heat-labile (LT) toxin of ETEC using Dot-Blot microfiltration and enzyme-linked immunosorbent assay (ELISA) methods. Paired stool samples were collected on the day of presentation and 5 days later. RESULTS: Twelve of 14 (86%) patients with ETEC diarrhea (5 heat-stable [ST]/LT positive, 4 LT-only, and 5 ST-only) developed sIgA antibodies directed against their homologous ETEC and 6 (66%) of the 9 patients harboring ST/LT or LT-only strains developed sIgA LT-antibody responses. Single fecal samples from 9 healthy controls were negative for ETEC specific antibodies. CONCLUSIONS: Patients with diarrhea due to noninvasive ST/LT ETEC and LT ETEC commonly produce a specific sIgA antibody response early in the illness. We feel that the methods employed will be useful to detect antibodies during natural infection by enteric pathogens and following oral enteric vaccine administration.

Improved detection of enterotoxigenic Escherichia coli among patients with travelers' diarrhea, by use of the polymerase chain reaction technique.

This study sought to determine whether a specific polymerase chain reaction (PCR) for enterotoxigenic Escherichia coli (ETEC) toxins after chaotropic extraction of DNA from stool would increase the detection of ETEC over that of conventional oligonucleotide probe hybridization of 5 E. coli colonies per stool sample (a standard method). By DNA hybridization, 29 (21%) of 140 patients were positive for ETEC, and 59 (42%) of 140 were positive for ETEC when PCR was used. Sensitivity of the PCR assay was confirmed through spiked stool experiments to be approximately 100-1000 ETEC colonies per sample. Specificity of the assay was determined by showing an absence of ETEC by the PCR technique in a subgroup of 48 subjects and by confirming the presence of ETEC DNA of positive samples by dot blot procedure. PCR technique detected significantly more ETEC infections in these subjects than did the hybridization method (P<.0001).

Nod factors of Rhizobium are a key to the legume door.

Symbiotic interactions between rhizobia and legumes are largely controlled by reciprocal signal exchange. Legume roots excrete flavonoids which induce rhizobial nodulation genes to synthesize and excrete lipo-oligosaccharide Nod factors. In turn, Nod factors provoke deformation of the root hairs and nodule primordium formation. Normally, rhizobia enter roots through infection threads in markedly curled root hairs. If Nod factors are responsible for symbiosis-specific root hair deformation, they could also be the signal for entry of rhizobia into legume roots. We tested this hypothesis by adding, at inoculation, NodNGR-factors to signal-production-deficient mutants of the broad-host-range Rhizobium sp. NGR234 and Bradyrhizobium japonicum strain USDA110. Between 10(-7) M and 10(-6) M NodNGR factors permitted these NodABC- mutants to penetrate, nodulate and fix nitrogen on Vigna unguiculata and Glycine max, respectively. NodNGR factors also allowed Rhizobium fredii strain USDA257 to enter and fix nitrogen on Calopogonium caeruleum, a nonhost. Detailed cytological investigations of V. unguiculata showed that the NodABC- mutant NGR delta nodABC, in the presence of NodNGR factors, entered roots in the same way as the wild-type bacterium. Since infection threads were also present in the resulting nodules, we conclude that Nod factors are the signals that permit rhizobia to penetrate legume roots via infection threads.