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Infection with aerosolized Francisella tularensisor Yersinia pestiscan lead to lethal disease in humans if treatment is not initiated promptly. Finafloxacin is a novel fluoroquinolone which has demonstrated broad-spectrum activity against a range of bacterial species in vitro, in vivo, and in humans, activity which is superior in acidic, infection-relevant conditions.

ABSTRACTBioluminescence imaging (BLI) enables real-time, noninvasive tracking of infection in vivoand longitudinal infection studies. In this study, a bioluminescent Francisella tularensisstrain, SCHU S4-lux, was used to develop an inhalational infection model in BALB/c mice. Mice were infected intranasally, and the progression of infection was monitored in real time using BLI. A bioluminescent signal was detectable from 3 days postinfection (3 dpi), initially in the spleen and then in the liver and lymph nodes, before finally becoming systemic. The level of bioluminescent signal correlated with bacterial numbers in vivo, enabling noninvasive quantification of bacterial burdens in tissues. Treatment with levofloxacin (commencing at 4 dpi) significantly reduced the BLI signal. Furthermore, BLI was able to distinguish noninvasively between different levofloxacin treatment regimens and to identify sites of relapse following treatment cessation. These data demonstrate that BLI and SCHU S4-luxare suitable for the study of F. tularensispathogenesis and the evaluation of therapeutics for tularemia.

Whole body imaging technologies, coupled with the generation of stable light emitting strains of infectious agents, make it possible to monitor the location and kinetics of agent growth inside an animal by noninvasive nonterminal methodologies throughout the course of the infection. However, imaging of viable hazardous pathogens, such as Yersinia pestis, requires specialized containment facilities to prevent contamination of both personnel and the wider environment. Here we describe the successful establishment of an in vivobioimaging capability specifically addressing the requirement for safe and secure work with hazard group 3 pathogens and demonstrate its utility for imaging mice infected with a bioluminescence producing strain of Y. pestis.

Whole body imaging technologies, coupled with the generation of stable light emitting strains of infectious agents, make it possible to monitor the location and kinetics of agent growth inside an animal by noninvasive nonterminal methodologies throughout the course of the infection. However, imaging of viable hazardous pathogens, such as Yersinia pestis, requires specialized containment facilities to prevent contamination of both personnel and the wider environment. Here we describe the successful establishment of an in vivobioimaging capability specifically addressing the requirement for safe and secure work with hazard group 3 pathogens and demonstrate its utility for imaging mice infected with a bioluminescence producing strain of Y. pestis.

ABSTRACTLiposome-encapsulated ciprofloxacin for inhalation (CFI) was investigated as a putative postexposure therapeutic for two strains of Francisella tularensis. The efficacies of oral ciprofloxacin and intranasally instilled CFI could not be distinguished in a mouse model of infection with the F. tularensislive vaccine strain (LVS), where a single dose of either formulation offered full protection against a lethal challenge. However, mouse studies with the more virulent Schu S4 strain of F. tularensisdemonstrated that a higher level of protection against a lethal aerosol infection is provided by CFI than by oral ciprofloxacin. In addition, using this infection model, it was possible to discriminate the efficacy of intranasally instilled CFI from that of aerosolized CFI, with aerosolized CFI providing full protection after just a single dose. The improved efficacy of CFI compared to oral ciprofloxacin is likely due to the high sustained concentrations of ciprofloxacin in the lung. In summary, CFI may be a promising therapy, perhaps enabling the prophylactic regimen to be shortened, for use in the event of a deliberate release of F. tularensis. The prophylactic efficacy of CFI against other biological warfare (BW) threat agents also warrants investigation.

Burkholderia pseudomallei is the causative agent of melioidosis, a disease endemic to regions of Southeast Asia and Northern Australia. Both humans and a range of other animal species are susceptible to melioidosis, and the production of a group 3 polysaccharide capsule in B. pseudomallei is essential for virulence. B. pseudomallei capsular polysaccharide (CPS) I comprises unbranched manno-heptopyranose residues and is encoded by a 34.5-kb locus on chromosome 1. Despite the importance of this locus, the role of all of the genes within this region is unclear. We inactivated 18 of these genes and analyzed their phenotype using Western blotting and immunofluorescence staining. Furthermore, by combining this approach with bioinformatic analysis, we were able to develop a model for CPS I biosynthesis and export. We report that inactivating gmhA, wcbJ, and wcbN in B. pseudomallei K96243 retains the immunogenic integrity of the polysaccharide despite causing attenuation in the BALB/c murine infection model. Mice immunized with the B. pseudomallei K96243 mutants lacking a functional copy of either gmhA or wcbJ were afforded significant levels of protection against a wild-type B. pseudomallei K96243 challenge.

Burkholderia pseudomalleiis the causative agent of melioidosis, a disease endemic to regions of Southeast Asia and Northern Australia. Both humans and a range of other animal species are susceptible to melioidosis, and the production of a group 3 polysaccharide capsule in B. pseudomalleiis essential for virulence. B. pseudomalleicapsular polysaccharide (CPS) I comprises unbranched manno-heptopyranose residues and is encoded by a 34.5-kb locus on chromosome 1. Despite the importance of this locus, the role of all of the genes within this region is unclear. We inactivated 18 of these genes and analyzed their phenotype using Western blotting and immunofluorescence staining. Furthermore, by combining this approach with bioinformatic analysis, we were able to develop a model for CPS I biosynthesis and export. We report that inactivating gmhA, wcbJ, and wcbNin B. pseudomalleiK96243 retains the immunogenic integrity of the polysaccharide despite causing attenuation in the BALB/c murine infection model. Mice immunized with the B. pseudomalleiK96243 mutants lacking a functional copy of either gmhAor wcbJwere afforded significant levels of protection against a wild-type B. pseudomalleiK96243 challenge.

ABSTRACTMacrophage infectivity potentiators (Mips) are a group of virulence factors encoded by pathogenic bacteria such as Legionella, Chlamydia, and Neisseriaspecies. Mips are part of the FK506-binding protein (FKBP) family, whose members typically exhibit peptidylprolyl cis-transisomerase (PPIase) activity which is inhibitable by the immunosuppressants FK506 and rapamycin. Here we describe the identification and characterization of BPSS1823, a Mip-like protein in the intracellular pathogen Burkholderia pseudomallei. Recombinant BPSS1823 protein has rapamycin-inhibitable PPIase activity, indicating that it is a functional FKBP. A mutant strain generated by deletion of BPSS1823in B. pseudomalleiexhibited a reduced ability to survive within cells and significant attenuation in vivo, suggesting that BPSS1823 is important for B. pseudomalleivirulence. In addition, pleiotropic effects were observed with a reduction in virulence mechanisms, including resistance to host killing mechanisms, swarming motility, and protease production.

Macrophage infectivity potentiators (Mips) are a group of virulence factors encoded by pathogenic bacteria such as Legionella, Chlamydia, and Neisseria species. Mips are part of the FK506-binding protein (FKBP) family, whose members typically exhibit peptidylprolyl cis-trans isomerase (PPIase) activity which is inhibitable by the immunosuppressants FK506 and rapamycin. Here we describe the identification and characterization of BPSS1823, a Mip-like protein in the intracellular pathogen Burkholderia pseudomallei. Recombinant BPSS1823 protein has rapamycin-inhibitable PPIase activity, indicating that it is a functional FKBP. A mutant strain generated by deletion of BPSS1823 in B. pseudomallei exhibited a reduced ability to survive within cells and significant attenuation in vivo, suggesting that BPSS1823 is important for B. pseudomallei virulence. In addition, pleiotropic effects were observed with a reduction in virulence mechanisms, including resistance to host killing mechanisms, swarming motility, and protease production.

ABSTRACTThe Burkholderia pseudomalleiK96243genome encodes six type VI secretion systems (T6SSs), but little is known about the role of these systems in the biology of B. pseudomallei. In this study, we purified recombinant Hcp proteins from each T6SS and tested them as vaccine candidates in the BALB/c mouse model of melioidosis. Recombinant Hcp2 protected 80% of mice against a lethal challenge with K96243, while recombinant Hcp1, Hcp3, and Hcp6 protected 50% of mice against challenge. Hcp6 was the only Hcp constitutively produced by B. pseudomallei in vitro; however, it was not exported to the extracellular milieu. Hcp1, on the other hand, was produced and exported in vitrowhen the VirAG two-component regulatory system was overexpressed in trans. We also constructed six hcpdeletion mutants (Δhcp1through Δhcp6) and tested them for virulence in the Syrian hamster model of infection. The 50% lethal doses (LD50s) for the Δhcp2through Δhcp6mutants were indistinguishable from K96243(<10 bacteria), but the LD50for the Δhcp1mutant was >103bacteria. The hcp1deletion mutant also exhibited a growth defect in RAW 264.7 macrophages and was unable to form multinucleated giant cells in this cell line. Unlike K96243, the Δhcp1mutant was only weakly cytotoxic to RAW 264.7 macrophages 18 h after infection. The results suggest that the cluster 1 T6SS is essential for virulence and plays an important role in the intracellular lifestyle of B. pseudomallei.

The Burkholderia pseudomallei K96243 genome encodes six type VI secretion systems (T6SSs), but little is known about the role of these systems in the biology of B. pseudomallei. In this study, we purified recombinant Hcp proteins from each T6SS and tested them as vaccine candidates in the BALB/c mouse model of melioidosis. Recombinant Hcp2 protected 80% of mice against a lethal challenge with K96243, while recombinant Hcp1, Hcp3, and Hcp6 protected 50% of mice against challenge. Hcp6 was the only Hcp constitutively produced by B. pseudomallei in vitro; however, it was not exported to the extracellular milieu. Hcp1, on the other hand, was produced and exported in vitro when the VirAG two-component regulatory system was overexpressed in trans. We also constructed six hcp deletion mutants (hcp1 through hcp6) and tested them for virulence in the Syrian hamster model of infection. The 50% lethal doses (LD50s) for the hcp2 through hcp6 mutants were indistinguishable from K96243 (<10 bacteria), but the LD50for the hcp1 mutant was >103bacteria. The hcp1 deletion mutant also exhibited a growth defect in RAW 264.7 macrophages and was unable to form multinucleated giant cells in this cell line. Unlike K96243, the hcp1 mutant was only weakly cytotoxic to RAW 264.7 macrophages 18 h after infection. The results suggest that the cluster 1 T6SS is essential for virulence and plays an important role in the intracellular lifestyle of B. pseudomallei.

This study investigated the in vitroactivity of finafloxacin against bacterial strain panels of the biodefense pathogens. Broth microdilution assays were performed at neutral and acidic pH to determine the effectiveness of the antibiotics under conditions typical of an intracellular environment. In all instances, finafloxacin demonstrated superior activity at low pH.

ABSTRACTBurkholderia pseudomalleiis the causative agent of melioidosis, a serious disease endemic in Southeast Asia and Northern Australia. Antibiotic treatment is lengthy and relapse often occurs. Finafloxacin is a novel fluoroquinolone with increased antibacterial activity in acidic conditions in contrast to other fluoroquinolones which demonstrate reduced activity at a lower pH. Therefore, finafloxacin may have improved efficacy against B. pseudomallei, which can survive within host cells where the local pH is acidic. In vitroanalysis was performed using MICs, minimal bactericidal concentrations (MBCs), time-kill assays, persister cell assays, and macrophage assays. Finafloxacin showed increased bactericidal activity at pH 5 in comparison to pH 7 and ciprofloxacin at pH 5. In vivostudies in BALB/c mice included pharmacokinetic studies to inform an appropriate dosing regimen. Finafloxacin efficacy was evaluated in an inhalational murine model of melioidosis where antibiotic treatment was initiated at 6 or 24 h postchallenge and continued for 14 days, and mice were observed for 63 days. The survival of infected mice following 14 days of treatment was 80%, 60% or 0% for treatments initiated at 6 h and 60%, 30% or 0% for treatments initiated at 24 h for finafloxacin, co-trimoxazole, or ciprofloxacin, respectively. In summary, finafloxacin has increased bactericidal activity for B. pseudomalleiunder acidic conditions in vitroand improves survival in a murine model of melioidosis compared with those for ciprofloxacin. Furthermore, finafloxacin improves bacteriological clearance compared with that of co-trimoxazole, suggesting it may offer an effective postexposure prophylaxis against B. pseudomallei.