Bacteria as solid phase in a concentration fluorescence immunoassay analysis of antibodies to surface antigens

Flagella allow uropathogenic Escherichia coli ascension into murine kidneys

Uropathogenic Escherichia coli (UPEC) cause bladder and kidney infections in humans and mice. UPEC initiate many kidney infections by ascending out of infected bladders, but how this occurs is not well understood. To determine if the flagella were responsible for the ascension of UPEC to the kidneys, a fliC mutation in strain NU149 was created. The fliC mutant spread poorly on soft agar plates, and 12h post-inoculation of murine urinary tracts, ascension into the murine kidneys was compromised in this mutant strain compared with wild-type bacteria. Complementation of the mutation restored the ability to spread on soft agar plates and ascend into the murine kidneys. To confirm the fliC mutant results, an anti-flagella monoclonal antibody that has been previously described inhibited the spread of UPEC strain NU149 on soft agar plates. When the anti-flagella antibody was mixed with strain NU149 cells and the antibody-treated bacterial cells were used to infect mice, significantly fewer mice had kidney infections than mice that were injected with strain NU149 cells mixed with normal mouse serum or anti-type 1 pili antibody. These results suggest that E. coli flagella may be of importance in allowing the bacteria to ascend from the bladder and initiate kidney infections in humans, and the use of an antibody against the flagella could prevent the spread of UPEC into the kidneys.

Down-regulation of the kps region 1 capsular assembly operon following attachment of Escherichia coli type 1 fimbriae to D-mannose receptors

A differential-display PCR procedure identified the capsular assembly gene kpsD after Escherichia coli type 1 fimbrial binding to mannose-coated Sepharose beads. Limiting-dilution reverse-transcribed PCRs confirmed down-regulation of the kpsD gene, and Northern blot and lacZ fusion analyses showed down-regulation of the kpsFEDUCS region 1 operon. KpsD protein levels fell, and an agglutination test showed less K capsular antigen on the surface following the bacterial ligand-receptor interaction. These data show that binding of type 1 fimbriae (pili) to d-mannose receptors triggers a cross talk that leads to down-regulation of the capsule assembly region 1 operon in uropathogenic E. coli.

Bacterial concentration fluorescence immunoassay (BCFIA) for the detection of periodontopathogens in plaque

A bacterial concentration fluorescence immunoassay (BCFIA) was developed to rapidly detect periodontopathic bacteria in human plaque samples. The BCFIA utilized fluorescent-tagged monoclonal antibodies (MAbs) directed against the lipopolysaccharide of selected Gram-negative bacteria. Microorganisms identified in plaque using the BCFIA included Actinobacillus actinomycetemcomitans, Porphyromonas gingivalis, Prevotella intermedia, and Fusobacterium nucleatum. The immunoassay procedure involved combining a patient's plaque sample with a species-specific fluorescein isothiocyanate-labeled MAb and then incubating the mixture in a specialized microtiter plate allowing the MAb to bind to its homologous bacteria. Bound and unbound fluorescent-tagged MAbs were separated by filtration and total bound bacterial fluorescence was determined with a fluorimeter. The relative number of a bacterial species in a given plaque sample was estimated by reference to a standard curve carried through the BCFIA. The BCFIA had a lower detection limit of near 10(4) specific bacterial cells in a mixed bacterial preparation or plaque sample. When compared to cultivable flora procedures in detecting the 4 periodontopathogens, the BCFIA had high levels of statistical sensitivity, 97% to 100%, while statistical specificity ranged between 57% and 92%. There was a 71% to 82% agreement between BCFIA and DNA probe methodology in detecting periodontopathogens in plaque. The BCFIA, when compared to cultivable flora, offers the advantage of evaluating both live and dead bacterial cells in plaque. This may in part, if not fully, explain the lower specificity values of the BCFIA when compared to cultivable flora. Screening plaque samples for periodontopathic bacteria is considerably faster and results in a greater frequency of detection with BCFIA than cultivable flora based methods.

Lewis blood group antigen expression by cultured normal ureteral epithelial cells

The importance of Lewis blood group antigens in recurrent urinary tract infections has led to a more detailed study of the expression of these antigens in an in vitro culture system. Expression of A, B, H, and Lewis blood group antigens by primary cultures of ureter epithelial cells was analyzed by flow cytometry. Cells maintained blood group determinants for up to 7 weeks in culture over three passages. In several specimens, the cells that exhibited expression of Lewis A (Le(a) and Lewis B (Le(b)) antigens increased dramatically over 2-3 passages in culture. Lewis Y (Le(y)) antigen expression was positive on all primary cultures tested. The effect of fetal bovine serum (FBS) on blood group antigen expression was evaluated. Increased concentrations of FBS in the growth media increased the expression of Le(a) and Le(b) antigens in certain specimens, but did not affect expression of the other blood group antigens. The effect of FBS on blood group antigen expression of cultured cells depended on the Lewis blood type of the individual donating the specimen. To evaluate the heterogeneity often seen in Le(a) and Le(b) antigen expression, dual staining of cells for Le(a) and Le(b) antigens was performed. The results of these studies show for the first time that Lewis blood group antigens are expressed by cultured normal ureteral epithelial cells and that the pattern of expression of Le(a) and Le(b) changes over time. Furthermore, an individual cell may simultaneously express more than one Lewis antigen on its surface.

Growth conditions mediate differential transcription of fim genes involved in phase variation of type 1 pili

Type 1 pili in Escherichia coli undergo phase variation in which individual cells in a population reversibly switch between piliated (Pil+) and nonpiliated (Pil-) states. The switching process is mediated by an invertible DNA fragment which contains the promoter for fimA, the gene encoding the major structural subunit of type 1 pili. Although type 1 pili randomly phase vary in broth cultures, many clinical isolates of E. coli do not express type 1 pili when cultured on agar media. We investigated the role of the invertible element and the upstream genes, fimB and fimE, in the agar-mediated suppression of pili in an agar-negative clinical isolate, strain 149. Southern hybridization and polymerase chain reaction analyses of the fimA promoter region in broth-grown 149 cells indicated that the invertible element was present in orientations corresponding to both Pil+ and Pil- phenotypes. In contrast, only one orientation of the invertible element, corresponding to the Pil- phenotype, was observed in strain 149 cells cultured on agar. A second clinical isolate, strain 2-7, which expresses type 1 pili on agar was also examined; the invertible element was found in both the Pil+ and Pil- orientations during growth of this strain on agar as well as in broth. The introduction of the fim gene cluster from strain J96 on a multicopy plasmid into agar-negative strain 149 resulted in the production of both J96 and 149 pili during growth on agar. Experiments with subclones of the J96 genes indicated that the presence of an intact fimB gene allowed strain 149 pili to be produced on agar. Differences in pilus production between agar and broth cultures appear to be the result of differential transcription of fimB and fimE under the two growth conditions. In contrast, the pattern of expression of these genes in agar phase-variable strain 2-7 did not differ between broth- and agar-grown cells.

Fluorescence immunoassay for detecting periodontal bacterial pathogens in plaque

A particle concentration fluorescence immunoassay has been modified into a bacterial concentration fluorescence immunoassay (BCFIA) to rapidly detect periodontopathic bacteria in human plaque samples. The BCFIA utilizes fluorescently tagged monoclonal antibodies (MAbs) directed against the lipopolysaccharide of selected gram-negative plaque bacteria. Microorganisms closely associated with periodontal disease that can be identified in plaque with the BCFIA include Porphyromonas gingivalis, Bacteroides intermedius, Actinobacillus actinomycetemcomitans, Fusobacterium nucleatum, and Eikenella corrodens. Briefly, the procedure involved mixing a patient's plaque sample or other bacterial preparation with a species-specific fluorescein isothiocyanate-labeled MAb in a specialized microtiter plate. This mixture was incubated to allow binding of the MAb to its homologous bacteria. The bound and unbound fluorescent tagged MAbs were separated by filtration in the modified microtiter plate, and the total bacterial bound fluorescence was determined with a fluorimeter. The number of a specific bacterial species in a given plaque sample or other bacterial suspension was estimated by reference to a primary standard carried through the BCFIA. The lower detection limit of the BCFIA was 10(3) to 10(4) bacterial cells from single cultures of bacteria or 10(4) bacterial cells in mixed cultures. The coefficient of variation within and between plates for each of the five bacterium-specific MAbs in screening plaque for the periodontal pathogens was less than 10%. These results demonstrate that microbes in plaque can be used as the solid phase in the BCFIA to detect and quantitate MAbs associated with specific bacteria quickly and reliably.