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Bilophila wadsworthia is a common inhabitant of the human colon and has been associated with appendicitis and other local sites of inflammation in humans. Challenge-exposure or prevalence studies in laboratory and other animals have not been reported. B. wadsworthia is closely related phylogenetically to Desulfovibrio sp. and Lawsonia intracellularis , which are considered colon pathogens. We developed a PCR specific for B. wadsworthia DNA. Samples of bacterial DNA extracted from the feces of pigs on six farms in Australia and four farms in Venezuela were examined. Specific DNA of B. wadsworthia was detected in the feces of 58 of 161 Australian and 2 of 45 Venezuelan pigs, results comprising 100% of the neonatal pigs, 15% of the weaned grower pigs, and 27% of the adult sows tested. Single-stranded conformational polymorphism analysis of PCR product DNA derived from pigs or from known human strains showed an identical pattern. Histologic examination of the intestines of weaned B. wadsworthia -positive pigs found no or minor specific lesions in the small and large intestines, respectively. B. wadsworthia is apparently a common infection in neonatal pigs, but its prevalence decreases after weaning. The possible role of B. wadsworthia as an infection in animals and in human colons requires further study.

The influence of growth medium and incubation conditions on the detection of Bilophila wadsworthia β-lactamase was tested with Cefinase and Cefinase Plus disks. The tests involved aerobic and anaerobic incubation with conventional disk and quantitative tube assays. The production of β-lactamase was correlated with penicillin G, ampicillin, and ampicillin-sulbactam MICs and inhibition zones on penicillin (2-U) disks. The strains were grown on (i) brucella agar (brucella), (ii) brucella agar supplemented with 1% pyruvate (brucella-pyruvate), and (iii) brucella agar supplemented with 1% taurine (brucella-taurine). With the aerobic disk assay, 100, 100, and 7% of strains were positive after 30 min from growth on brucella-pyruvate, brucella, and brucella-taurine plates, respectively; of strains grown on brucella-taurine, 54% remained negative by the Cefinase assay, and 23% remained negative by the Cefinase Plus assay at 2 h. In quantitative assays, the strains became positive after 30 min from brucella-pyruvate plates and after 1 h from brucella plates. The intensities of the reactions were strongest with brucella-pyruvate plates under anaerobic test conditions. Anaerobic incubation enhanced β-lactamase detection of growth on brucella-taurine: at 3 h, 85% of strains were positive in comparison to 38% with aerobic incubation. All β-lactamase-negative strains were susceptible to penicillin G and ampicillin; all β-lactamase-positive strains were resistant to ampicillin and, with the exception of two strains, penicillin G. In conclusion, β-lactamase production correlated with susceptibility to penicillin G and ampicillin. Brucella agar supplemented with 1% pyruvate was the most reliable medium for testing B. wadsworthia β-lactamase, and anaerobic incubation expedited positive results. Brucella agar supplemented with taurine was unsuitable for B. wadsworthia β-lactamase testing. Cefinase and Cefinase Plus results were in agreement, but Cefinase Plus yielded faster reactions.

Portions of the 16S RNA from a urease-positive Bilophila wadsworthia strain were sequenced, and a probe was constructed. The probe was end labeled with [32P]ATP and polynucleotide kinase and hybridized on a nylon filter (by dot blot hybridization) to the immobilized rRNA of 12 B. wadsworthia strains and eight other anaerobic isolates. The probe efficiently hybridized only to the Bilophila strains. Cross-reactivity at high RNA levels (2,000 ng) was observed with one strain of Bacteroides thetaiotamicron and one strain of Bacteroides fragilis (with 10x SET buffer [20x SET buffer is 0.5 M NaCl, 0.03 M Tris, and 2 mM EDTA]) but was not seen at lower RNA levels or with 5x SET buffer. When tested against mixed cultures of aerobic and anaerobic isolates representative of appendiceal abscess flora, the probe did not react with mixed cultures containing no Bilophila cells and could detect > or = 10(5) Bilophila CFU/ml when the mixture was seeded with Bilophila cells. This probe is of potential use in the rapid identification of pure isolates and in the direct identification of B. wadsworthia in clinical specimens.

Bilophila wadsworthia, a recently described anaerobic gram-negative bacillus, was isolated from blood cultures of two patients with liver abscesses. These isolates exhibited the expected phenotypic characteristics, and identification was confirmed by cell wall fatty acid analysis by gas-liquid chromatography. This is the first documentation of bacteremia due to B. wadsworthia.