Production and Characterization of Rat Monoclonal Antibodies against the PAL Antigen of Legionella spp

The purpose of this work was to obtain genus-specific monoclonal antibodies against the Legionella spp. recombinant PAL protein, which will subsequently allow to use them as a basis for the development of new express tests for pathogenic legionella detection. A short three-week immunization protocol for Wistar rats was used to generate rat-mouse heterohybridomas producing antibodies against PAL. Mouse myeloma cell line Sp2/0-Ag14 served as the fusion partner. Hybridization was performed using two methods: PEG-mediated fusion and electrofusion. Subsequent screening was performed by indirect solid-phase ELISA against the target protein rPAL. Specificity analysis was performed by dot-blot using a panel of lysates obtained from 39 pure cultures of different strains, which included closely related and heterologous microorganisms among others. No difference in the efficiency of stable hybridoma clones production by the two indicated cell-fusion methods was detected. Twelve clones producing specific rat monoclonal antibodies were obtained based on the screening results. The obtained rat monoclonal antibodies are highly specific towards the PAL protein of L. pneumophila of different serological groups and other pathogenic legionella and are good candidates to be used as the components of diagnostic test systems for the detection of pathogenic representatives of the Legionella genus.

Effect of 4-Hexylresorcinol on the Efficiency of Antibiotic Treatment of Experimental Sepsis Caused by Antibiotic-Resistant Klebsiella pneumoniae Strain in Mice

High efficiency of a combined preparation including synergistic polymyxin B and 4-hexylresorcinol was shown for treatment of experimental sepsis caused by an antibiotic-resistant highly virulent hypermucoid Klebsiella pneumoniae strain KPM9Pm^r in mice. Complex therapy with polymyxin B (1 mg/kg) and 4-hexylresorcinol (30 mg/kg) led to cure in 80%; in 20% of these mice, no bacterial cells were found. After treatment with polymyxin B alone, only 50% animals survived and all of them contained bacterial cells. Comparative analysis of the results of monotherapy and combined treatment indicates that 4-hexylresorcinol not only increases the efficiency of antibiotic, but also minimizes persistence of the infection agent and therefore, the risk of development of antibiotic resistance.

Selective Protective Potency of Yersinia pestis ΔnlpD Mutants

It has recently been shown that the NlpD lipoprotein is essential to Yersinia pestis virulence and that subcutaneous administration of the nlpD mutant could protect mice against bubonic and pneumonic plague better than the EV vaccine strain [PLoS One 2009. V. 4. № 9. e7023]. In this study, similar nlpD mutants were generated on the basis of other Y. pestis parent strains, including strains from the subspecies microtus, which is avirulent to guinea pigs and humans. Comparative testing confirmed that immunization of mice with nlpD mutants induces immunity 105 times more potent than the one induced by the administration of the EV vaccine strain. At the same time, NlpD- bacteria failed to protect guinea pigs in the case of a subcutaneous challenge with Y. pestis, inducing a 106 times less potent protection compared with that conferred by immunization with the EV vaccine strain. The possible causes of the observed phenomena are discussed.

Selective Protective Potency of Yersinia pestis ΔnlpD Mutants

It has recently been shown that the NlpD lipoprotein is essential to Yersinia pestis virulence and that subcutaneous administration of the nlpD mutant could protect mice against bubonic and pneumonic plague better than the EV vaccine strain [PLoS One 2009. V. 4. № 9. e7023]. In this study, similar ΔnlpD mutants were generated on the basis of other Y. pestis parent strains, including strains from the subspecies microtus, which is avirulent to guinea pigs and humans. Comparative testing confirmed that immunization of mice with ΔnlpD mutants induces immunity 105 times more potent than the one induced by the administration of the EV vaccine strain. At the same time, NlpD- bacteria failed to protect guinea pigs in the case of a subcutaneous challenge with Y. pestis, inducing a 106 times less potent protection compared with that conferred by immunization with the EV vaccine strain. The possible causes of the observed phenomena are discussed.

[CONSTRUCTION AND PROPERTIES OF THE FRANCISELLA TULARENSIS VACCINE STRAIN WITHOUT ONE COPY OF THE IGLC GENE AND WITHOUT RECA GENE]

The live vaccine based on the Francisella tularensis subsp. holarctica vaccine strain 15 NIIEG line is used in Russia against tularemia. This vaccine is highly effective, but fairly unstable. Therefore, development of stable live tularemia vaccine with minimal side effect is rather urgent. The method of allel removal in the F. tularensis vaccine strain was used to remove one copy of the iglC gene, which is required to provide intracellular production of the vaccine strain, as well as removal of the recA gene. The latter is crucial for homological recombination. pGM5 suicide vector based on pHV33 bireplicon plasmid was constructed to provide replacement of intact F. tularensis chromosome segments by modified segments. Modified chromosome segments contain F. Tularensis DNA fragment without iglC structural gene segment 545 p. b. (in pGMΔiglC plasmid), as well as DNA fragment containing no recA structural gene segment 1060 p.b. (pGMΔrecA plasmid). The constructed 15/23-1ΔrecA mutant, in contrast to the vaccine strain 15, was capable of reproducing in the macrophage-like cells J774A.1 line, whereas the efficiency of the reproduction was 8-10 times less. BALB/c mouse responded to immunization by the 15/23-1ΔrecA strain by smaller weight decrease (-2%) as compared to the strain 15 (-14%). Bacteria of the 15/23-1ΔrecA strain were virtually incapable of germinating from the BALB/c murine spleen 14 days after invasion, whereas bacteria of the strain 15 were found in the murine organs even after 21 days. The F. tularensis 15/23-1ΔrecA strain having smaller reaction ability can be used as a basis for construction of stable live safe tularemia vaccine.

[Efficacy of enterocin S760 in treatment of mice with anthrax infection due to Bacillus anthracis M-71]

The therapeutic efficacy of enterocin S760, a broad spectrum antimicrobial peptide produced by Enterococcus faecium LWP760 was tested on mice infected with Bacillus anthracis M-71 to induce anthrax (second Tsenkovsky's vaccine). Intraperitoneal four-, two- or one-fold administration of the peptide in a dose of 25 mg/kg for 10 days for prophylactic (1 hour after the contamination) and therapeutic (24 hours after the contamination) purposes prevented or cured the infection in 90-100% of the mice versus the 100-percent lethality in the control (untreated animals). The antimicrobial activity of enterocin S760 against B. anthracis M-71 in vivo correlated with activity in vitro. Enterocin S760 is considered a novel promising antimicrobial for the treatment of grampositive and gramnegative infections.

Biological properties and structure of the lipopolysaccharide of a vaccine strain of Francisella tularensis generated by inactivation of a quorum sensing system gene qseC

A knockout mutant with a deletion in a quorum sensing system gene qseC was generated from the vaccine strain Francisella tularensis 15 by site-directed mutagenesis. The variant with the inactivated gene qseC differed from the parental strain in growth rate on solid nutrient medium but had the same growth dynamics in liquid nutrient medium. The mutation abolished almost completely the resistance of the vaccine strain to normal rabbit serum and its ability to survive in macrophages; in addition, the strain lost the residual virulence. A significant phenotypic alteration was observed in the lipopolysaccharide of F. tularensis. Particularly, the mutant strain synthesized no noticeable amount of the lipopolysaccharide with the high-molecular-mass O-polysaccharide, presumably as a result of impairing biosynthesis of the repeating unit, namely, a loss of the ability to incorporate a formyl group, an N-acyl substituent of 4-amino-4,6-dideoxy-D-glucose.

[Use of enterocin S760 for prevention and treatment of experimental Salmonella infection in mice]

AIM

To demonstrate treatment efficacy of bacteriocin S760 synthesized by Enterococcus faecium 760 for septic Salmonella infection in mice.

MATERIALS AND METHODS

One hundred mice, which were intraperitoneally inoculated with 100 LD50 of Salmonella enteritidis strain 92 Rif(r), received bacteriocin 1 hour (prevention) or 48 hours (treatment) after inoculation in doses 25, 50, or 100 mg/kg every 6 hours during 5 or 10 days.

RESULTS

Use of peptide S760 for prophylaxis in dose 50 mg/kg during 10 days prevented lethal infection in 100% of animals, whereas its use for treatment cured 70% of animals with generalized salmonellosis. Shortening of treatment course from 10 to 5 days and reducing dose of bacteriocin led to less pronounced treatment effect but in all animals it was expressed by increase of mean length of life compared to control (not treated).

CONCLUSION

Obtained results demonstrated high treatment efficacy of bacteriocin S760 during septic salmonellosis and perspectives of its use in medicine and animal health.