Detection of Yersinia pestis over time in seeded bottled water samples by cultivation on heart infusion agar

New Bacteriophages with Podoviridal Morphotypes Active against Yersinia pestis: Characterization and Application Potential

Phages of highly pathogenic bacteria represent an area of growing interest for bacterial detection and identification and subspecies typing, as well as for phage therapy and environmental decontamination. Eight new phages-YpEc56, YpEc56D, YpEc57, YpEe58, YpEc1, YpEc2, YpEc11, and YpYeO9-expressing lytic activity towards Yersinia pestis revealed a virion morphology consistent with the Podoviridae morphotype. These phages lyse all 68 strains from 2 different sets of Y. pestis isolates, thus limiting their potential application for subtyping of Y. pestis strains but making them rather promising in terms of infection control. Two phages-YpYeO9 and YpEc11-were selected for detailed studies based on their source of isolation and lytic cross activity towards other Enterobacteriaceae. The full genome sequencing demonstrated the virulent nature of new phages. Phage YpYeO9 was identified as a member of the Teseptimavirus genus and YpEc11 was identified as a member of the Helsettvirus genus, thereby representing new species. A bacterial challenge assay in liquid microcosm with a YpYeO9/YpEc11 phage mixture showed elimination of Y. pestis EV76 during 4 h at a P/B ratio of 1000:1. These results, in combination with high lysis stability results of phages in liquid culture, the low frequency of formation of phage resistant mutants, and their viability under different physical-chemical factors indicate their potential for their practical use as an antibacterial mean.

MAPt: A Rapid Antibiotic Susceptibility Testing for Bacteria in Environmental Samples as a Means for Bioterror Preparedness

Antibiotic resistance of bio-threat agents holds major concerns especially in light of advances in methods for engineering pathogens with antibiotic resistance. Preparedness means for rapid identification and prompt proper medical treatment are of need to contain the event and prevent morbidity and spreading of the disease by properly treating exposed individuals before symptoms appearance. Herein, we describe a novel, rapid, simple, specific, and sensitive method named Micro-Agar-PCR-test (MAPt), which determines antibiotic susceptibility of bio-terror pathogens, directly from environmental samples, with no need for any prior isolation, quantification, or enrichment steps. As proof of concept, we have used this approach to obtain correct therapeutic antibiotic minimal inhibitory concentration (MIC) values for the Tier-1 select agents, Bacillus anthracis, Yersinia pestis, and Francisella tularensis, spiked in various environmental samples recapitulating potential bioterror scenarios. The method demonstrated efficiency for a broad dynamic range of bacterial concentrations, both for fast-growing as well as slow-growing bacteria and most importantly significantly shortening the time for accurate results from days to a few hours. The MAPt allows us to address bioterror agents-contaminated environmental samples, offering rational targeted prophylactic treatment, before the onset of morbidity in exposed individuals. Hence, MAPt is expected to provide data for decision-making personal for treatment regimens before the onset of symptoms in infected individuals.

Deliberate release: Plague - A review

Yersinia pestis is the causative agent of plague and is considered one of the most likely pathogens to be used as a bioweapon. In humans, plague is a severe clinical infection that can rapidly progress with a high mortality despite antibiotic therapy. Therefore, early treatment of Y. pestis infection is crucial. This review provides an overview of its clinical manifestations, diagnosis, treatment, prophylaxis, and protection requirements for the use of clinicians.

We discuss the likelihood of a deliberate release of plague and the feasibility of obtaining, isolating, culturing, transporting and dispersing plague in the context of an attack aimed at a westernized country. The current threat status and the medical and public health responses are reviewed. We also provide a brief review of the potential prehospital treatment strategy and vaccination against Y. pestis. Further, we discuss the plausibility of antibiotic resistant plague bacterium, F1-negative Y. pestis, and also the possibility of a plague mimic along with potential strategies of defense against these. An extensive literature search on the MEDLINE, EMBASE, and Web of Science databases was conducted to collate papers relevant to plague and its deliberate release. Our review concluded that the deliberate release of plague is feasible but unlikely to occur, and that a robust public health response and early treatment would rapidly halt the transmission of plague in the population. Front-line clinicians should be aware of the potential of a deliberate release of plague and prepared to instigate early isolation of patients. Moreover, front-line clinicians should be weary of the possibility of suicide attackers and mindful of the early escalation to public health organizations.

Development of a rapid viability polymerase chain reaction method for detection of Yersinia pestis

Due to the occurrence of natural plague outbreaks and its historical usage as a biological weapon, Yersinia pestis is considered one of the high-priority biological threat agents. It can remain viable in certain environments including water for >100 days. Because of its slow-growth characteristic, it usually takes three or more days to detect and confirm the identity of viable Y. pestis cells by PCR, serological, or biochemical assays when using the traditional microbiological plate-culture-based analysis, and that too, assuming faster growing microbes present in a water sample do not mask the Y. pestis colonies and interfere with analysis. Therefore, a rapid-viability Polymerase Chain Reaction (RV-PCR) method was developed for detection of Y. pestis. The RV-PCR method combines 24 h-incubation broth culture in a 48-well plate, and pre- and post-incubation differential PCR analyses, thereby allowing for rapid and high-throughput sample analysis compared with the current plate culture method. One chromosomal and two plasmid gene target-based real-time PCR assays were down-selected, showing ca. 10 genome equivalent detection; the chromosomal assay was then used for RV-PCR method development. A 10¹-cell level (10-99 cells) sensitivity of detection was demonstrated even with complex sample backgrounds including known PCR inhibitors (ferrous sulfate and humic acid), as well as metal oxides and microbes present in Arizona Test Dust (ATD). The method sensitivity was maintained in the presence of dead Y. pestis cells up to 10⁴ cells per sample. While affording high-throughput and rapid sample analysis, the 48-well plate format used in this method for sample enrichment significantly reduced labor requirements and generation of BioSafety Level-3 (BSL-3) laboratory waste as compared to the usual microbiological plate-culture-based methods. This method may serve as a model for other vegetative bacterial pathogens.

Structural Characterisation of the Beta-Ketoacyl-Acyl Carrier Protein Synthases, FabF and FabH, of Yersinia pestis

Yersinia pestis, the causative agent of bubonic, pneumonic, and septicaemic plague, remains a major public health threat, with outbreaks of disease occurring in China, Madagascar, and Peru in the last five years. The existence of multidrug resistant Y. pestis and the potential of this bacterium as a bioterrorism agent illustrates the need for new antimicrobials. The β-ketoacyl-acyl carrier protein synthases, FabB, FabF, and FabH, catalyse the elongation of fatty acids as part of the type II fatty acid biosynthesis (FASII) system, to synthesise components of lipoproteins, phospholipids, and lipopolysaccharides essential for bacterial growth and survival. As such, these enzymes are promising targets for the development of novel therapeutic agents. We have determined the crystal structures of the Y. pestis β-ketoacyl-acyl carrier protein synthases FabF and FabH, and compared these with the unpublished, deposited structure of Y. pestis FabB. Comparison of FabB, FabF, and FabH provides insights into the substrate specificities of these enzymes, and investigation of possible interactions with known β-ketoacyl-acyl carrier protein synthase inhibitors suggests FabB, FabF and FabH may be targeted simultaneously to prevent synthesis of the fatty acids necessary for growth and survival.

Detection of Yersinia pestis in environmental and food samples by intact cell immunocapture and liquid chromatography-tandem mass spectrometry

Yersinia pestis is the causative agent of bubonic and pneumonic plague, an acute and often fatal disease in humans. In addition to the risk of natural exposure to plague, there is also the threat of a bioterrorist act, leading to the deliberate spread of the bacteria in the environment or food. We report here an immuno-liquid chromatography-tandem mass spectrometry (immuno-LC-MS/MS) method for the direct (i.e., without prior culture), sensitive, and specific detection of Y. pestis in such complex samples. In the first step, a bottom-up proteomics approach highlighted three relevant protein markers encoded by the Y. pestis-specific plasmids pFra (murine toxin) and pPla (plasminogen activator and pesticin). Suitable proteotypic peptides were thoroughly selected to monitor the three protein markers by targeted MS using the selected reaction monitoring (SRM) mode. Immunocapture conditions were optimized for the isolation and concentration of intact bacterial cells from complex samples. The immuno-LC-SRM assay has a limit of detection of 2 × 10(4) CFU/mL in milk or tap water, which compares well with those of state-of-the-art immunoassays. Moreover, we report the first direct detection of Y. pestis in soil, which could be extremely useful in confirming Y. pestis persistence in the ground.

Fast and simple detection of Yersinia pestis applicable to field investigation of plague foci

Yersinia pestis, the plague bacillus, has a rodent-flea-rodent life cycle but can also persist in the environment for various periods of time. There is now a convenient and effective test (F1-dipstick) for the rapid identification of Y. pestis from human patient or rodent samples, but this test cannot be applied to environmental or flea materials because the F1 capsule is mostly produced at 37°C. The plasminogen activator (PLA), a key virulence factor encoded by a Y. pestis-specific plasmid, is synthesized both at 20°C and 37°C, making it a good candidate antigen for environmental detection of Y. pestis by immunological methods. A recombinant PLA protein from Y. pestis synthesized by an Escherichia coli strain was used to produce monoclonal antibodies (mAbs). PLA-specific mAbs devoid of cross-reactions with other homologous proteins were further cloned. A pair of mAbs was selected based on its specificity, sensitivity, comprehensiveness, and ability to react with Y. pestis strains grown at different temperatures. These antibodies were used to develop a highly sensitive one-step PLA-enzyme immunoassay (PLA-EIA) and an immunostrip (PLA-dipstick), usable as a rapid test under field conditions. These two PLA-immunometric tests could be valuable, in addition to the F1-disptick, to confirm human plague diagnosis in non-endemic areas (WHO standard case definition). They have the supplementary advantage of allowing a rapid and easy detection of Y. pestis in environmental and flea samples, and would therefore be of great value for surveillance and epidemiological investigations of plague foci. Finally, they will be able to detect natural or genetically engineered F1-negative Y. pestis strains in human patients and environmental samples.

Detection and Isolation of Yersinia pestis Without Fraction 1 Antigen by Monoclonal Antibody in Foods and Water

Most available immunoassays for Yersinia pestis are based on the detection of fraction 1 antigen (F1) when yersiniae are grown at 37°C. A monoclonal antibody (MAb) was developed based on the detection of surface antigens that are not F1. F1-deficient Y. pestis cells were induced and used to immunize BALB/c mice from which MAb (immunoglobulin G1), which specifically recognizes Y. pestis, with or without F1, was obtained. This MAb (6B5) did not cross-react with enteric bacteria, including Yersinia enterocolitica. Enzyme-linked immunosorbent assay results revealed that MAb 6B5 is specific for Y. pestis, with the exception of a minor cross-reaction with Yersinia pseudotuberculosis. Western immunoblot analysis revealed that MAb 6B5 recognizes a Y. pestis outer membrane protein of ca. 30 kDa. Magnetic beads that were coated with MAb 6B5 were compared with beads coated with polyclonal antibody (PAb; rabbit) against Y. pestis for the isolation of Y. pestis in food and water samples by using a PATHATRIX cell concentration apparatus. Enrichment cultures of Y. pestis in different foods by using two different times (6 and 24 h) in brain heart infusion broth at 37°C were evaluated. Results revealed MAb 6B5–coated magnetic beads were equivalent to magnetic beads coated with PAb against Y. pestis A1122 whole cells in concentrating Y. pestis for isolation, especially when samples were enriched for 6 h. However, the selectivity for Y. pestis of the magnetic beads coated with MAb 6B5 was greater than that coated with PAb.

Survival and persistence of nonspore-forming biothreat agents in water

AIMS

To determine whether nonspore-forming biothreat agents can survive and persist in potable water that does not contain a disinfectant.

METHODS AND RESULTS

 Autoclaved, de-chlorinated Atlanta municipal water was inoculated with eight isolates of bacterial biothreat agents (10⁶ CFU ml⁻¹). The inoculated water samples were incubated at 5, 8 (Francisella tularensis only) or 25°C and assayed for viability by culture and by the presence of metabolic activity as measured by esterase activity (ScanRDI, AES Chemunex). Viability as determined by culture varied from 1 to 30 days, depending upon the organism and the temperature of the water. All organisms were determined viable as measured by esterase activity for the entire 30 days, regardless of the incubation temperature.

CONCLUSION

 Francisella tularensis was culturable for at least 21 days if held at 8°C. The remaining nonspore-forming bacterial biothreat agents were found to be metabolically active for at least 30 days in water held at 5 or 25°C.

SIGNIFICANCE AND IMPACT OF THE STUDY

 The data can assist public health officials to determine the safety of drinking water after contamination with a biothreat agent.

Entry of Yersinia pestis into the viable but nonculturable state in a low-temperature tap water microcosm

Yersinia pestis, the causative agent of plague, has caused several pandemics throughout history and remains endemic in the rodent populations of the western United States. More recently, Y. pestis is one of several bacterial pathogens considered to be a potential agent of bioterrorism. Thus, elucidating potential mechanisms of survival and persistence in the environment would be important in the event of an intentional release of the organism. One such mechanism is entry into the viable but non-culturable (VBNC) state, as has been demonstrated for several other bacterial pathogens. In this study, we showed that Y. pestis became nonculturable by normal laboratory methods after 21 days in a low-temperature tap water microcosm. We further show evidence that, after the loss of culturability, the cells remained viable by using a variety of criteria, including cellular membrane integrity, uptake and incorporation of radiolabeled amino acids, and protection of genomic DNA from DNase I digestion. Additionally, we identified morphological and ultrastructural characteristics of Y. pestis VBNC cells, such as cell rounding and large periplasmic spaces, by electron microscopy, which are consistent with entry into the VBNC state in other bacteria. Finally, we demonstrated resuscitation of a small number of the non-culturable cells. This study provides compelling evidence that Y. pestis persists in a low-temperature tap water microcosm in a viable state yet is unable to be cultured under normal laboratory conditions, which may prove useful in risk assessment and remediation efforts, particularly in the event of an intentional release of this organism.