Whole-cell vaccine candidates induce a protective response against virulent Acinetobacter baumannii.

Acinetobacter baumannii causes multi-system diseases in both nosocomial settings and a pre-disposed general population. The bacterium is not only desiccation-resistant but also notoriously resistant to multiple antibiotics and drugs of last resort including carbapenem, colistin, and sulbactam. The World Health Organization has categorized carbapenem-resistant A. baumannii at the top of its critical pathogen list in a bid to direct urgent countermeasure development. Several early-stage vaccines have shown a range of efficacies in healthy mice, but no vaccine candidates have advanced into clinical trials. Herein, we report our findings that both an ionizing γ-radiation-inactivated and a non-ionizing ultraviolet C-inactivated whole-cell vaccine candidate protects neutropenic mice from pulmonary challenge with virulent AB5075, a particularly pathogenic isolate. In addition, we demonstrate that a humoral response is sufficient for this protection via the passive immunization of neutropenic mice.

Radiation-Inactivated Acinetobacter baumannii Vaccine Candidates.

Acinetobacter baumannii is a bacterial pathogen that is often multidrug-resistant (MDR) and causes a range of life-threatening illnesses, including pneumonia, septicemia, and wound infections. Some antibiotic treatments can reduce mortality if dosed early enough before an infection progresses, but there are few other treatment options when it comes to MDR-infection. Although several prophylactic strategies have been assessed, no vaccine candidates have advanced to clinical trials or have been approved. Herein, we rapidly produced protective whole-cell immunogens from planktonic and biofilm-like cultures of A. baumannii, strain AB5075 grown using a variety of methods. After selecting a panel of five cultures based on distinct protein profiles, replicative activity was extinguished by exposure to 10 kGy gamma radiation in the presence of a Deinococcus antioxidant complex composed of manganous (Mn2+) ions, a decapeptide, and orthophosphate. Mn2+ antioxidants prevent hydroxylation and carbonylation of irradiated proteins, but do not protect nucleic acids, yielding replication-deficient immunogenic A. baumannii vaccine candidates. Mice were immunized and boosted twice with 1.0 × 107 irradiated bacterial cells and then challenged intranasally with AB5075 using two mouse models. Planktonic cultures grown for 16 h in rich media and biofilm cultures grown in static cultures underneath minimal (M9) media stimulated immunity that led to 80-100% protection.

A novel gamma radiation-inactivated sabin-based polio vaccine.

A concerted action on the part of international agencies and national governments has resulted in the near-eradication of poliomyelitis. However, both the oral polio vaccine (OPV) and the inactivated polio vaccine (IPV) have deficiencies which make them suboptimal for use after global eradication. OPV is composed of attenuated Sabin strains and stimulates robust immunity, but may revert to neurovirulent forms in the intestine which can be shed and infect susceptible contacts. The majority of IPV products are manufactured using pathogenic strains inactivated with formalin. Upon eradication, the production of large quantities of pathogenic virus will present an increased biosecurity hazard. A logical ideal endgame vaccine would be an inactivated form of an attenuated strain that could afford protective immunity while safely producing larger numbers of doses per unit of virus stock than current vaccines. We report here the development of an ionizing radiation (IR)-inactivated Sabin-based vaccine using a reconstituted Mn-decapeptide (MDP) antioxidant complex derived from the radioresistant bacterium Deinococcus radiodurans. In bacteria, Mn2+-peptide antioxidants protect proteins from oxidative damage caused by extreme radiation exposure. Here we show for the first time, that MDP can protect immunogenic neutralizing epitopes in picornaviruses. MDP protects epitopes in Polio Virus 1 and 2 Sabin strains (PV1-S and PV2-S, respectively), but viral genomic RNA is not protected during supralethal irradiation. IR-inactivated Sabin viruses stimulated equivalent or improved neutralizing antibody responses in Wistar rats compared to the commercially used IPV products. Our approach reduces the biosecurity risk of the current PV vaccine production method by utilizing the Sabin strains instead of the wild type neurovirulent strains. Additionally, the IR-inactivation approach could provide a simpler, faster and less costly process for producing a more immunogenic IPV. Gamma-irradiation is a well-known method of virus inactivation and this vaccine approach could be adapted to any pathogen of interest.

Tick-borne encephalitis virus, Kyrgyzstan.

Tick-borne encephalitis virus (TBEV) is an emerging pathogen in Europe and Asia. We investigated TBEV in Kyrgyzstan by collecting small mammals and ticks from diverse localities and analyzing them for evidence of TBEV infection. We found TBEV circulating in Kyrgyzstan much farther south and at higher altitudes than previously reported.

Understanding the genetic consequences of environmental toxicant exposure: Chernobyl as a model system.

We sampled vole populations in Ukraine with the dual goal of characterizing population diversity and of providing a biogeographic perspective to evaluate experimental designs used for previous studies. Our data indicate that genetic diversity in bank vole populations is widely variable across regions and that diversity estimates in contaminated sites are unremarkable compared to those in uncontaminated areas. Furthermore, the relative frequencies of haplotypes have remained statistically identical throughout multiple sampling periods. Thus, the genetic data from bank vole populations in Ukraine fail to support the hypothesis that mutational changes in contaminated regions are the product of exposure to Chernobyl radiation. Our results suggest that genetic diversity in radioactive regions of Ukraine is probably a function of natural geographic variation rather than increased mutational pressure from radiation exposure and underscore the importance of adequate geographic sampling in studies designed to elucidate the effects of toxicant exposure.

Mitochondrial control region variation in bank voles (Clethrionomys glareolus) is not related to Chernobyl radiation exposure.

Three previous studies at Chernobyl, Ukraine, documented elevated mitochondrial DNA diversity in bank voles (Clethrionomys glareolus) from radioactively contaminated sites. Little evidence was found to link patterns of diversity in contaminated areas to radiation exposure, but the experimental design precluded discriminating among alternative explanations for elevated diversity in exposed groups. Reference sites selected for the studies were relatively distant from contaminated sites and, additionally, were separated from contaminated sites by large river systems; thus, we hypothesized that differences among sites were correlated with geographic isolation rather than with radiation exposure. For the present study, we added three reference sites, which were selected based on minimal radioactive contamination, proximity to contaminated sites, and absence of obvious barriers to dispersal. We hypothesized that neighboring reference sites should exhibit levels and patterns of diversity similar to those of contaminated sites if the previously detected differences were, in fact, caused by geographic isolation. Indeed, levels of diversity in nearby reference sites are comparable to levels in contaminated sites. Additionally, nearby reference sites contain several haplotypes not observed at other study sites. Our results suggest that levels of diversity in contaminated regions are more plausibly explained by ecological and historical factors than by increased mutational pressure resulting from exposure to Chernobyl radiation.