Identification of alcaligin as the siderophore produced by Bordetella pertussis and B. bronchiseptica

The siderophores produced by iron-starved Bordetella pertussis and B. bronchiseptica were purified and were found to be identical. Using mass spectrometry and proton nuclear magnetic resonance, we determined that the siderophore produced by these organisms was identical to alcaligin, a siderophore produced by Alcaligenes denitrificans.

The microbicidal agent C31G inhibits Chlamydia trachomatis infectivity in vitro

Safe and effective vaginal microbicidal compounds are being sought to offer women an independent method for protection against transmission of sexually acquired pathogens. The purpose of this study was to examine the efficacy of two formulations of one such compound, C31G, against Chlamydia trachomatis serovar E alone, its host epithelial cell (HEC-1B) alone, and against chlamydiae-infected HEC-1B cells. Preexposure of isolated, purified infectious chlamydial elementary bodies (EB) to C31G, at pHs 7.2 and 5.7, for 1 h at 4 degrees C resulted in reduced infectivity of EB for HEC-1B cells. Examination of the C31G-exposed 35S-EB on sodium dodecyl sulfate-polyacrylamide gel electrophoresis autoradiographs and by Western blotting revealed a C31G concentration-dependent and pH-dependent destabilization of the chlamydial envelope, resulting in the release of chlamydial lipopolysaccharide and proteins. Interestingly, when the host human genital columnar epithelial cells were infected with chlamydiae and then exposed to dilute concentrations of C31G which did not alter epithelial cell viability, chlamydial infectivity was also markedly reduced. C31G gained access to the developing chlamydial inclusion causing damage to or destruction of metabolically active reticulate bodies as well as apparent alteration of the inclusion membrane, which resulted in premature escape of chlamydial antigen to the infected epithelial surface. These studies show that the broad-spectrum antiviral and antibacterial microbicide C31G also has antichlamydial activity.

Accelerated development of genital Chlamydia trachomatis serovar E in McCoy cells grown on microcarrier beads

Chlamydia trachomatis serovar E is a major cause of bacterially-acquired sexually transmitted infections. Stock cultures of these obligate intracellular bacteria are often propogated in McCoy cells. We recently reported that greater infectious titers of chlamydiae could be obtained if the McCoy cells were cultured on collagen-coated microcarrier beads versus plastic flasks, although the reason for the difference in efficiency was not clear. This study analyzed the development of C. trachomatis grown in McCoy cells by the two methods. Transmission electron microscopy analysis revealed an accelerated chlamydial development, with maturation of reticulate bodies into elementary bodies sooner in McCoy cells grown on the porous substratum. Comparison of particle counts versus infectivity titers indicated the production of fewer numbers of elementary bodies but which were highly infectious sooner from the infected McCoy cell-microcarrier bead cultures than from duplicate infected McCoy cell cultures grown in plastic tissue culture flasks.

Calcium ion involvement in the action of Pasteurella haemolytica leukotoxin

The influence of Ca2+ ions on the cytotoxic activity of Pasteurella haemolytica leukotoxin was investigated. The divalent cation influenced the cytotoxic effect of the leukotoxin for sensitive BL-3 target cells, but its absence did not eliminate cytotoxicity. In short-term 1-h assays using neutral red uptake as a measure of cell viability, depletion of Ca2+ either by exhaustive dialysis or by addition of the Ca2+ chelators EDTA and EGTA eliminated the cytolytic effect of low doses of the toxin. Addition of Ca2+ to target cell cultures depleted of the divalent cation restored the cytolytic effect of the leukotoxin. Prolonged exposure of the BL-3 cells to the toxin abrogated the protective effect of EDTA and EGTA. Cell death measured by uptake of neutral red, exclusion of trypan blue and 51Cr release indicated that protection observed in the absence of free Ca2+ was temporary. Toxin-induced cytolysis equivalent to that observed in the presence of Ca2+ occurred following the initial 2-h exposure. In addition, verapamil, a Ca2+ channel blocker, prevented cell death during 1-h cytotoxicity assays. The protection afforded by verapamil was dose-dependent and was influenced by the concentration of Ca2+ in the buffer medium. The results suggest that Ca2+ positively influences the rapid initial phase of cell death resulting from exposure to the toxin, but is not required for the entirety of the cytolytic process.

Characterization of a neutralizing monoclonal antibody to Pasteurella haemolytica leukotoxin

Six hybridoma clones producing monoclonal antibodies (MAbs) reactive with Pasteurella haemolytica A1 leukotoxin were derived from mice immunized with leukotoxin excised from sodium dodecyl sulfate-polyacrylamide gels. Of the six MAbs, only one, Ltx-2, neutralized leukotoxin in a BL-3 cell cytotoxicity assay. MAb Ltx-2 blocked association of A1 leukotoxin to BL-3 cells, as measured by flow cytometric analysis. The epitope recognized by Ltx-2 was localized to the carboxyl half of the native protein, between residues 450 and 939, by Western immunoblot analysis of CNBr fragments. Further analysis with leukotoxin deletion proteins indicated either that the Ltx-2-reactive epitope was localized in the carboxyl portion of the leukotoxin between amino acids 768 and 939 or that this region influences MAb recognition of the epitope. MAb Ltx-2 was tested for neutralizing activity against leukotoxin produced by P. haemolytica serotypes 1 through 12. The MAb neutralized leukotoxin produced by all of the A biotype isolates (serotypes 1, 5, 6, 7, 8, 9, and 12), with the exception of serotype A2, but did not neutralize any T biotype leukotoxin tested (T3, T4, or T10). The results indicate that MAb Ltx-2 neutralizes leukotoxin by interfering with target cell association and that the MAb-specific epitope is either not present or not critical for function in the leukotoxin produced by P. haemolytica serotypes A2, T3, T4, and T10.