Characterization of the Salmonella bacteriophage vB_SenS-Ent1.

The bacteriophage vB_SenS-Ent1 (Ent1) is a member of the family Siphoviridae of tailed bacteriophages and infects a broad range of serovars of the enteric pathogen Salmonella enterica. The virion particle is composed of an icosahedral head 64 nm in diameter and a flexible, non-contractile tail of 116 × 8.5 nm possessing terminal fibres. The adsorption rate constant at 37 °C is 6.73 × 10(-9) ml min(-1). Latent and eclipse periods are 25 and 20 min, respectively, and the burst size is 35 progeny particles per cell after 35 min at 37 °C. Sequencing revealed a circularly permuted, 42 391 bp dsDNA genome containing 58 ORFs organized into four major transcriptional units. Comparisons with the genome sequences of other bacteriophages revealed a high level of nucleotide sequence identity and shared orthologous proteins with the Salmonella phages SETP3, SE2 and KS7 (SS3e) and the Escherichia phages K1G, K1H, K1ind1 and K1ind3.

A bioluminescent microbial biosensor for in vitro pretreatment assessment of cytarabine efficacy in leukemia.

BACKGROUND: The nucleoside analog cytarabine (Ara-C [cytosine arabinoside]) is the key agent for treating acute myeloid leukemia (AML); however, up to 30% of patients fail to respond to treatment. Screening of patient blood samples to determine drug response before commencement of treatment is needed. This project aimed to construct and evaluate a self-bioluminescent reporter strain of Escherichia coli for use as an Ara-C biosensor and to design an in vitro assay to predict Ara-C response in clinical samples. METHODS: We used transposition mutagenesis to create a cytidine deaminase (cdd)-deficient mutant of E. coli MG1655 that responded to Ara-C. The strain was transformed with the luxCDABE operon and used as a whole-cell biosensor for development an 8-h assay to determine Ara-C uptake and phosphorylation by leukemic cells. RESULTS: Intracellular concentrations of 0.025 µmol/L phosphorylated Ara-C were detected by significantly increased light output (P < 0.05) from the bacterial biosensor. Results using AML cell lines with known response to Ara-C showed close correlation between the 8-h assay and a 3-day cytotoxicity test for Ara-C cell killing. In retrospective tests with 24 clinical samples of bone marrow or peripheral blood, the biosensor-based assay predicted leukemic cell response to Ara-C within 8 h. CONCLUSIONS: The biosensor-based assay may offer a predictor for evaluating the sensitivity of leukemic cells to Ara-C before patients undergo chemotherapy and allow customized treatment of drug-sensitive patients with reduced Ara-C dose levels. The 8-h assay monitors intracellular Ara-CTP (cytosine arabinoside triphosphate) levels and, if fully validated, may be suitable for use in clinical settings.

Bacteria isolated from parasitic nematodes--a potential novel vector of pathogens?

Bacterial pathogens are ubiquitous in soil and water - concurrently so are free-living helminths that feed on bacteria. These helminths fall into two categories; the non-parasitic and the parasitic. The former have been the focus of previous work, finding that bacterial pathogens inside helminths are conferred survival advantages over and above bacteria alone in the environment, and that accidental ingestion of non-parasitic helminths can cause systemic infection in vertebrate hosts. Here, we determine the potential for bacteria to be associated with parasitic helminths. After culturing helminths from fecal samples obtained from livestock the external bacteria were removed. Two-hundred parasitic helminths from three different species were homogenised and the bacteria that were internal to the helminths were isolated and cultured. Eleven different bacterial isolates were found; of which eight were indentified. The bacteria identified included known human and cattle pathogens. We concluded that bacteria of livestock can be isolated in parasitic helminths and that this suggests a mechanism by which bacteria, pathogenic or otherwise, can be transmitted between individuals. The potential for helminths to play a role as pathogen vectors poses a potential livestock and human health risk. Further work is required to assess the epidemiological impact of this finding.

Intracellular cytarabine triphosphate in circulating blasts post-treatment predicts remission status in patients with acute myeloid leukemia.

Cytarabine remains the backbone of therapy in acute myeloid leukemia (AML). The ability to assess intracellular cytarabine triphosphate (ara-CTP) levels in patients receiving cytarabine represents a major goal in the prediction of treatment response. This study, conducted within a clinical setting, aimed to assess ara-CTP levels in circulating peripheral blasts from non-M3 AML patients receiving cytarabine at one of three dosing levels, using a novel biosensor assay. Results from the initial 72 hours post-commencement were correlated with day 28 remission status, with feasibility parameters concurrently assessed. Intracellular ara-CTP was detectable in ex vivo blasts post-treatment for standard-dose (SD) and high-dose (HD) patients (p < 0.05), and quantification revealed a 27-fold increase in intracellular steady-state concentration between the two dosing levels. For low-dose cytarabine, high rates of patient discharge and low intracellular concentrations limited analysis; however, assessment of intracellular ara-CTP concentration was achievable in a dwindling population of blasts for SD and HD treatment cohorts, with 4 hours post-treatment commencement potentially being most predictive of clinical response (r = -0.912, p = 0.0113). Concurrent assessment of peripheral leukemia-associated immunophenotype (LAIP)-positive cells revealed a decline in burden (0-72 hours), which correlated with remission status (p < 0.05). Unexpectedly high rates of night sampling led to challenges associated with sampling rates, but did not have an impact on patient compliance. Additional training of night staff improved feasibility substantially. Multiple peripheral sampling during the initial 72 hours of treatment is feasible in newly diagnosed patients, and ara-CTP is detectable over the initial 24 hours, facilitating prediction of chemosensitivity of leukemic blasts to cytarabine.

CPX-351 exhibits hENT-independent uptake and can be potentiated by fludarabine in leukaemic cells lines and primary refractory AML.

CPX-351, a liposomal formulation co-encapsulating cytarabine and daunorubicin (DNR) in a synergistic 5:1 M ratio, has shown favourable response in newly diagnosed elderly high-risk AML. This study assessed intracellular ara-CTP levels following in vitro exposure of human immortalised leukaemic cell lines and primary AML blasts to CPX-351, and investigated fludarabine potentiation of intracellular ara-CTP formation from CPX-351. Comparison of intracellular handling of CPX-351 to cytarabine in HL-60 cells indicated slower conversion to ara-CTP for CPX-351, but equivalent cytotoxicity to cytarabine and combined DNR/cytarabine (DA) at 48 h, mostly likely reflecting the need for intracellular liposome processing to release encapsulated drugs. Further assessment demonstrated cytotoxicity of CPX-351 to be superior to DA at 48 and 72 h in cytarabine-resistant THP-1 cells (p < 0.001), and this effect could not be inhibited upon blockade of human equilibrative nucleoside transporter (hENT) function with dipyridamole. Assessment of Flu-CPX in primary blasts from presentation AML patients (n = 5) demonstrated a more rapid and pronounced potentiation of ara-CTP from CPX-351 than in immortalised cell lines, with 4/5 patients showing significant increases in ara-CTP, notably for those that went on to fail induction and relapse treatment in vivo (n = 3). This suggests a favourable impact on patient outcome from Flu-CPX.

Rapid in-vitro testing for chemotherapy sensitivity in leukaemia patients.

Bioluminescent bacterial biosensors can be used in a rapid in vitro assay to predict sensitivity to commonly used chemotherapy drugs in acute myeloid leukemia (AML). The nucleoside analog cytarabine (ara-C) is the key agent for treating AML; however, up to 30 % of patients fail to respond to treatment. Screening of patient blood samples to determine drug response before commencement of treatment is needed. To achieve this aim, a self-bioluminescent reporter strain of Escherichia coli has been constructed and evaluated for use as an ara-C biosensor and an in vitro assay has been designed to predict ara-C response in clinical samples. Transposition mutagenesis was used to create a cytidine deaminase (cdd)-deficient mutant of E. coli MG1655 that responded to ara-C. The strain was transformed with the luxCDABE operon and used as a whole-cell biosensor for development an 8-h assay to determine ara-C uptake and phosphorylation by leukemic cells. Intracellular concentrations of 0.025 µmol/L phosphorylated ara-C were detected by significantly increased light output (P < 0.05) from the bacterial biosensor. Results using AML cell lines with known response to ara-C showed close correlation between the 8-h assay and a 3-day cytotoxicity test for ara-C cell killing. In retrospective tests with 24 clinical samples of bone marrow or peripheral blood, the biosensor-based assay predicted leukemic cell response to ara-C within 8 h. The biosensor-based assay may offer a predictor for evaluating the sensitivity of leukemic cells to ara-C before patients undergo chemotherapy and allow customized treatment of drug-sensitive patients with reduced ara-C dose levels. The 8-h assay monitors intracellular ara-CTP (cytosine arabinoside triphosphate) levels and, if fully validated, may be suitable for use in clinical settings.

Investigation and verification of a bioluminescent biosensor for the quantitation of ara-CTP generation: a biomarker for cytosine arabinoside sensitivity in acute myeloid leukaemia.

A novel whole cell bacterial biosensor, which emits light in response to the active metabolite of cytosine arabinoside (ara-C, cytarabine), ara-CTP, has been investigated and verified. The biosensor has been formulated as an ex vivo assay, designed for peripheral blood or bone marrow cells, which can produce a clinical result within a working day. The nucleoside analogue ara-C is a key agent for treatment of acute myeloid leukaemia (AML); treatment decisions are made rapidly with AML, patients often receiving same-day commencement of chemotherapy. Currently no rapid predictive test is available to select appropriate therapy for patients prior to treatment. Experiments were designed to determine optimal assay conditions using leukaemic cell lines. We observed a significant increase (~15 fold) in bioluminescence signal compared to control after 8-h incubation of the biosensor with ara-C. This corresponded to a >2-log increase in light output per bacterial cell. Interestingly, bioluminescence conferred a survival advantage to the bacteria following ara-C treatment. The assay is sensitive (lower limit of quantitation of 0.05 µM), selective, accurate (≤ 15% RE) and precise (≤ 15% coefficient of variation) over a linear concentration range of ara-CTP (0.05-0.5 µM), and detection is independent of reaction volume. Recovery of added standard was tested using ex vivo patient leukaemic cells (n=5). Stability studies on lyophilized bacterial biosensor were performed to ensure maintenance of performance over 12 months. The biosensor assay could be invaluable to the clinician, assisting with treatment selection, and potentially mitigating the risks of resistance and toxicity observed with this drug.

A novel bioluminescent bacterial biosensor for measurement of Ara-CTP and cytarabine potentiation by fludarabine in seven leukaemic cell lines.

This study evaluates an in vitro biosensor assay capable of detecting the intracellular levels of the tri-phosphorylated form of cytarabine (Ara-CTP) within one working day. The biosensor predicted the response of seven leukaemic cell lines with varying known sensitivities to cytarabine alone and in combination with fludarabine. High-performance liquid chromatography (HPLC), 3-day assessment of cellular viable mass, and flow cytometric assessment of apoptosis were used to validate biosensor performance. A correlation between the biosensor results and Ara-CTP quantitation by HPLC was confirmed (R=0.972). The biosensor was also capable of detecting enhanced accumulation of Ara-CTP following sequential pre-treatment of leukaemic cells with cytarabine ± fludarabine.

Use of bioluminescent bacterial biosensors to investigate the role of free-living helminths as reservoirs and vectors of Salmonella.

Free-living microbivorous helminths that consume pathogenic bacteria could offer an environmental refuge for those pathogens and also, in the case of accidental ingestion, could transmit food-borne pathogens to humans and livestock. We tested this hypothesis by comparing the survival of Salmonella bacteria that had been ingested by the helminth Caenorhabditis elegans with that of the bacteria alone, in a series of experiments to mimic harsh environmental conditions. Using lux gene technology to record the in vivo growth of Salmonella we found that when inside C. elegans, the Salmonella exhibited enhanced survival at pH 2 and 3, in the presence of chlorine and when exposed to UV irradiation, thereby providing an environmental refuge or reservoir for the bacteria. On inoculating laboratory mice with C. elegans that had been fed on bioluminescent Salmonella, real-time imaging showed that animals developed a systemic bacterial infection, indicating that free-living helminths could play a role as a vector of pathogens.

Stimulation of DNA repair and increased light output in response to UV irradiation in Escherichia coli expressing lux genes.

It has previously been suggested that the evolutionary drive of bacterial bioluminescence is a mechanism of DNA repair. By assessing the UV sensitivity of Escherichia coli, it is shown that the survival of UV-irradiated E. coli constitutively expressing luxABCDE in the dark is significantly better than either a strain with no lux gene expression or the same strain expressing only luciferase (luxAB) genes. This shows that UV resistance is dependent on light output, and not merely on luciferase production. Also, bacterial survival was found to be dependent on the conditions following UV irradiation, as bioluminescence-mediated repair was not as efficient as repair in visible light. Moreover, photon emission revealed a dose-dependent increase in light output per cell after UV exposure, suggesting that increased lux gene expression correlates with UV-induced DNA damage. This phenomenon has been previously documented in organisms where the lux genes are under their natural luxR regulation but has not previously been demonstrated under the regulation of a constitutive promoter.

Antimicrobial properties of milk: dependence on presence of xanthine oxidase and nitrite.

Human and bovine milk inhibited the metabolic activity of Escherichia coli, as shown by luminescence monitoring of constructs expressing the luxCDABE genes. Inhibition was dependent on both xanthine oxidase (XO) activity and on the presence of nitrite, implying that XO-generated nitric oxide functions as an antibacterial agent.