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Multi-pathogens sequence containing plasmids as positive controls for universal detection of potential agents of bioterrorism.

Charrel RN, La Scola B, Raoult D - BMC Microbiol. (2004)

Bottom Line: False-positive results due to contamination by the positive control were easily detected by sequencing and eliminated by digestion with NotI.It is also possible to avoid or to ensure immediate detection of false positive results due to contamination by positive controls using these plasmids.These plasmids and the corresponding primers and probes are immediately available for all clinical microbiology laboratories provided they have molecular amplification equipment.

View Article: PubMed Central - HTML - PubMed

Affiliation: Unité des Rickettsies, CNRS UMR 6020 IFR 48, Faculté de Médecine, Marseille, France. rnc-virophdm@pop.gulliver.fr

ABSTRACT

Background: The limited circulation of many of the agents that are likely to be used in a bioterrorism attack precludes the ready availability of positive controls. This means that only specialized laboratories can screen for the presence of these agents by nucleic amplification assays. Calibrated controls are also necessary for quantitative measurements. Primers and probes to be used in both conventional and real-time PCR assays were designed for the detection of agents likely to be used by a bioterrorist. Three plasmids, each of which contains 4 to 6 specific sequences from agents on the CDC Category A and B list (excluding RNA viruses) were constructed. Two plasmids incorporate the sequences of Category A and B agents, respectively. The third plasmid incorporates sequences from Variola major and organisms that cause rash-like illnesses that may be clinically confused with smallpox. An "exogenic sequence", introducing a NotI restriction site was incorporated in the native sequences of the bioterrorism agents inserted in plasmids. The designed molecular system for detection of bioterrorism agents was tested on each of these agents (except Monkeypox virus, Smallpox virus and 2 Burkholderia species for which no native DNA was available) and a collection of 50 isolates of C. burnetii using constructed plasmids as positive controls.

Results: Designed primers and probes allowed molecular detection, in either single or multiplex assays, of agent-specific targets with analytical sensitivities of between 1 and 100 DNA copies. The plasmids could be used as positive controls. False-positive results due to contamination by the positive control were easily detected by sequencing and eliminated by digestion with NotI.

Conclusion: Plasmid A and B can be used as positive controls in molecular assays for the detection of bioterrorism agents in clinical specimens or environmental samples. Plasmid C can be used as a positive control in differentiation of vesicular rashes. It is also possible to avoid or to ensure immediate detection of false positive results due to contamination by positive controls using these plasmids. These plasmids and the corresponding primers and probes are immediately available for all clinical microbiology laboratories provided they have molecular amplification equipment.

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Related in: MedlinePlus

Construction of DNA control plasmid designed for the 4 CDC Category A DNA agents (Smallpox virus [seq1], Bacillus anthracis [seq2], Francisella tularensis [seq3], and Yersinia pestis [seq4]). Assembling of the smallpox virus and B. anthracis sequences is presented as an example. Successive steps are indicated by framed numbers. 1, PCR amplification of the two matrix sequences by primers consisting of the stabilization and the restriction site sequences (italics). PCR reactions were carried out in a volume of 50 μl that included 10 mM Tris-HCl [pH 9.0], 1.5 mM MgCl2, 50 mM KCl, 0.1% Triton X-100, 200 μM each dNTP, 0.4 μM of each oligonucleotide primer, 0.4 μM of the single stranded DNA, and 1.5 U of Taq DNA polymerase (Invitrogen, Cergy-Pontoise, France). The thermocycler (Biometra, Göttingen, Germany) profile was 5 min at 95°C, followed by 35 cycles of 30 sec at 95°C, 30 sec at 55°C, and 1 min at 72°C, and terminated by a final extension for 7 min at 72°C. PCR products were electrophorezed in 3% TAE-agarose gel containing ethidium bromide and visualized under UV transillumination. Column purification of the PCR products. PCR products of the expected size were column-purified by using the QIAquick PCR Purification Kit (Qiagen, Hilden, Germany) according to the manufacturer's instructions, and eluted in 50 μl of RNase free distillated water. When two bands or more were observed by gel analysis, the band of expected size was excised from the gel and purified by glass milk extraction with the GenClean III Kit (Q-Bio-Gene, Carlsbad CA, USA). 2, assemblage was conducted by pair, seq1 with seq2 (resulting in seq1-2). Equal volumes (10 μl) of purified seq1- and seq2-dsDNA were incubated at 37°C in the presence of Sac I. Sac I site is located at the 3' and 5' ends of seq1 and seq2, respectively. 3, the reaction product was column purified using the protocol aforementioned to discard the 15-nt DNA fragments corresponding to the 5' and 3' ends to avoid their re-ligation to their respective complementary sequences at step 5. 4, Overnight incubation at 4°C in the presence of T4 DNA ligase. Ten μl of the reaction was incubated with T4 DNA ligase (Roche, Basel, Switzerland) according to the manufaturer's instructions. 5, PCR amplification by using the external primers (italics) was performed according to the protocol described at step 1. Then column purification using the protocol detailed at step 2 of the resulting PCR product. At this step the seq1-2 PCR product may be cloned into PGEM-T for storage. The same procedure was performed for seq3 and seq4. Ultimately, seq1-2 and seq3-4 were assembled by using the same protocol (sections 1–9). The final product cloned into PGEM-T plasmid includes seq1-2-3-4 flanked by the two Sseq and restriction sites.
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Figure 2: Construction of DNA control plasmid designed for the 4 CDC Category A DNA agents (Smallpox virus [seq1], Bacillus anthracis [seq2], Francisella tularensis [seq3], and Yersinia pestis [seq4]). Assembling of the smallpox virus and B. anthracis sequences is presented as an example. Successive steps are indicated by framed numbers. 1, PCR amplification of the two matrix sequences by primers consisting of the stabilization and the restriction site sequences (italics). PCR reactions were carried out in a volume of 50 μl that included 10 mM Tris-HCl [pH 9.0], 1.5 mM MgCl2, 50 mM KCl, 0.1% Triton X-100, 200 μM each dNTP, 0.4 μM of each oligonucleotide primer, 0.4 μM of the single stranded DNA, and 1.5 U of Taq DNA polymerase (Invitrogen, Cergy-Pontoise, France). The thermocycler (Biometra, Göttingen, Germany) profile was 5 min at 95°C, followed by 35 cycles of 30 sec at 95°C, 30 sec at 55°C, and 1 min at 72°C, and terminated by a final extension for 7 min at 72°C. PCR products were electrophorezed in 3% TAE-agarose gel containing ethidium bromide and visualized under UV transillumination. Column purification of the PCR products. PCR products of the expected size were column-purified by using the QIAquick PCR Purification Kit (Qiagen, Hilden, Germany) according to the manufacturer's instructions, and eluted in 50 μl of RNase free distillated water. When two bands or more were observed by gel analysis, the band of expected size was excised from the gel and purified by glass milk extraction with the GenClean III Kit (Q-Bio-Gene, Carlsbad CA, USA). 2, assemblage was conducted by pair, seq1 with seq2 (resulting in seq1-2). Equal volumes (10 μl) of purified seq1- and seq2-dsDNA were incubated at 37°C in the presence of Sac I. Sac I site is located at the 3' and 5' ends of seq1 and seq2, respectively. 3, the reaction product was column purified using the protocol aforementioned to discard the 15-nt DNA fragments corresponding to the 5' and 3' ends to avoid their re-ligation to their respective complementary sequences at step 5. 4, Overnight incubation at 4°C in the presence of T4 DNA ligase. Ten μl of the reaction was incubated with T4 DNA ligase (Roche, Basel, Switzerland) according to the manufaturer's instructions. 5, PCR amplification by using the external primers (italics) was performed according to the protocol described at step 1. Then column purification using the protocol detailed at step 2 of the resulting PCR product. At this step the seq1-2 PCR product may be cloned into PGEM-T for storage. The same procedure was performed for seq3 and seq4. Ultimately, seq1-2 and seq3-4 were assembled by using the same protocol (sections 1–9). The final product cloned into PGEM-T plasmid includes seq1-2-3-4 flanked by the two Sseq and restriction sites.

Mentions: Targeted genes, sequences, probes and primers are summarized in Table 1, 2 and additional file 1. Targeted sequences of the 3 plasmids demonstrated that they were identical to the in silico predicted sequences. The specific sequences of plasmids CatA, CatB and CatVEF have been deposited in Genbank database under AY333963, AY333965, and AY333966 accession numbers, respectively. The construction of CatA is represented in Figures 1 and 2. E. coli strains harboring these plasmids are deposited at the CNCM collection (CNCM, Paris, France) under numbers I3087, I3088 and I3089, respectively. The sequences of the plasmids were verified after they were sent back by the CNCM for verification in our laboratory.


Multi-pathogens sequence containing plasmids as positive controls for universal detection of potential agents of bioterrorism.

Charrel RN, La Scola B, Raoult D - BMC Microbiol. (2004)

Construction of DNA control plasmid designed for the 4 CDC Category A DNA agents (Smallpox virus [seq1], Bacillus anthracis [seq2], Francisella tularensis [seq3], and Yersinia pestis [seq4]). Assembling of the smallpox virus and B. anthracis sequences is presented as an example. Successive steps are indicated by framed numbers. 1, PCR amplification of the two matrix sequences by primers consisting of the stabilization and the restriction site sequences (italics). PCR reactions were carried out in a volume of 50 μl that included 10 mM Tris-HCl [pH 9.0], 1.5 mM MgCl2, 50 mM KCl, 0.1% Triton X-100, 200 μM each dNTP, 0.4 μM of each oligonucleotide primer, 0.4 μM of the single stranded DNA, and 1.5 U of Taq DNA polymerase (Invitrogen, Cergy-Pontoise, France). The thermocycler (Biometra, Göttingen, Germany) profile was 5 min at 95°C, followed by 35 cycles of 30 sec at 95°C, 30 sec at 55°C, and 1 min at 72°C, and terminated by a final extension for 7 min at 72°C. PCR products were electrophorezed in 3% TAE-agarose gel containing ethidium bromide and visualized under UV transillumination. Column purification of the PCR products. PCR products of the expected size were column-purified by using the QIAquick PCR Purification Kit (Qiagen, Hilden, Germany) according to the manufacturer's instructions, and eluted in 50 μl of RNase free distillated water. When two bands or more were observed by gel analysis, the band of expected size was excised from the gel and purified by glass milk extraction with the GenClean III Kit (Q-Bio-Gene, Carlsbad CA, USA). 2, assemblage was conducted by pair, seq1 with seq2 (resulting in seq1-2). Equal volumes (10 μl) of purified seq1- and seq2-dsDNA were incubated at 37°C in the presence of Sac I. Sac I site is located at the 3' and 5' ends of seq1 and seq2, respectively. 3, the reaction product was column purified using the protocol aforementioned to discard the 15-nt DNA fragments corresponding to the 5' and 3' ends to avoid their re-ligation to their respective complementary sequences at step 5. 4, Overnight incubation at 4°C in the presence of T4 DNA ligase. Ten μl of the reaction was incubated with T4 DNA ligase (Roche, Basel, Switzerland) according to the manufaturer's instructions. 5, PCR amplification by using the external primers (italics) was performed according to the protocol described at step 1. Then column purification using the protocol detailed at step 2 of the resulting PCR product. At this step the seq1-2 PCR product may be cloned into PGEM-T for storage. The same procedure was performed for seq3 and seq4. Ultimately, seq1-2 and seq3-4 were assembled by using the same protocol (sections 1–9). The final product cloned into PGEM-T plasmid includes seq1-2-3-4 flanked by the two Sseq and restriction sites.
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Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC425577&req=5

Figure 2: Construction of DNA control plasmid designed for the 4 CDC Category A DNA agents (Smallpox virus [seq1], Bacillus anthracis [seq2], Francisella tularensis [seq3], and Yersinia pestis [seq4]). Assembling of the smallpox virus and B. anthracis sequences is presented as an example. Successive steps are indicated by framed numbers. 1, PCR amplification of the two matrix sequences by primers consisting of the stabilization and the restriction site sequences (italics). PCR reactions were carried out in a volume of 50 μl that included 10 mM Tris-HCl [pH 9.0], 1.5 mM MgCl2, 50 mM KCl, 0.1% Triton X-100, 200 μM each dNTP, 0.4 μM of each oligonucleotide primer, 0.4 μM of the single stranded DNA, and 1.5 U of Taq DNA polymerase (Invitrogen, Cergy-Pontoise, France). The thermocycler (Biometra, Göttingen, Germany) profile was 5 min at 95°C, followed by 35 cycles of 30 sec at 95°C, 30 sec at 55°C, and 1 min at 72°C, and terminated by a final extension for 7 min at 72°C. PCR products were electrophorezed in 3% TAE-agarose gel containing ethidium bromide and visualized under UV transillumination. Column purification of the PCR products. PCR products of the expected size were column-purified by using the QIAquick PCR Purification Kit (Qiagen, Hilden, Germany) according to the manufacturer's instructions, and eluted in 50 μl of RNase free distillated water. When two bands or more were observed by gel analysis, the band of expected size was excised from the gel and purified by glass milk extraction with the GenClean III Kit (Q-Bio-Gene, Carlsbad CA, USA). 2, assemblage was conducted by pair, seq1 with seq2 (resulting in seq1-2). Equal volumes (10 μl) of purified seq1- and seq2-dsDNA were incubated at 37°C in the presence of Sac I. Sac I site is located at the 3' and 5' ends of seq1 and seq2, respectively. 3, the reaction product was column purified using the protocol aforementioned to discard the 15-nt DNA fragments corresponding to the 5' and 3' ends to avoid their re-ligation to their respective complementary sequences at step 5. 4, Overnight incubation at 4°C in the presence of T4 DNA ligase. Ten μl of the reaction was incubated with T4 DNA ligase (Roche, Basel, Switzerland) according to the manufaturer's instructions. 5, PCR amplification by using the external primers (italics) was performed according to the protocol described at step 1. Then column purification using the protocol detailed at step 2 of the resulting PCR product. At this step the seq1-2 PCR product may be cloned into PGEM-T for storage. The same procedure was performed for seq3 and seq4. Ultimately, seq1-2 and seq3-4 were assembled by using the same protocol (sections 1–9). The final product cloned into PGEM-T plasmid includes seq1-2-3-4 flanked by the two Sseq and restriction sites.
Mentions: Targeted genes, sequences, probes and primers are summarized in Table 1, 2 and additional file 1. Targeted sequences of the 3 plasmids demonstrated that they were identical to the in silico predicted sequences. The specific sequences of plasmids CatA, CatB and CatVEF have been deposited in Genbank database under AY333963, AY333965, and AY333966 accession numbers, respectively. The construction of CatA is represented in Figures 1 and 2. E. coli strains harboring these plasmids are deposited at the CNCM collection (CNCM, Paris, France) under numbers I3087, I3088 and I3089, respectively. The sequences of the plasmids were verified after they were sent back by the CNCM for verification in our laboratory.

Bottom Line: False-positive results due to contamination by the positive control were easily detected by sequencing and eliminated by digestion with NotI.It is also possible to avoid or to ensure immediate detection of false positive results due to contamination by positive controls using these plasmids.These plasmids and the corresponding primers and probes are immediately available for all clinical microbiology laboratories provided they have molecular amplification equipment.

View Article: PubMed Central - HTML - PubMed

Affiliation: Unité des Rickettsies, CNRS UMR 6020 IFR 48, Faculté de Médecine, Marseille, France. rnc-virophdm@pop.gulliver.fr

ABSTRACT

Background: The limited circulation of many of the agents that are likely to be used in a bioterrorism attack precludes the ready availability of positive controls. This means that only specialized laboratories can screen for the presence of these agents by nucleic amplification assays. Calibrated controls are also necessary for quantitative measurements. Primers and probes to be used in both conventional and real-time PCR assays were designed for the detection of agents likely to be used by a bioterrorist. Three plasmids, each of which contains 4 to 6 specific sequences from agents on the CDC Category A and B list (excluding RNA viruses) were constructed. Two plasmids incorporate the sequences of Category A and B agents, respectively. The third plasmid incorporates sequences from Variola major and organisms that cause rash-like illnesses that may be clinically confused with smallpox. An "exogenic sequence", introducing a NotI restriction site was incorporated in the native sequences of the bioterrorism agents inserted in plasmids. The designed molecular system for detection of bioterrorism agents was tested on each of these agents (except Monkeypox virus, Smallpox virus and 2 Burkholderia species for which no native DNA was available) and a collection of 50 isolates of C. burnetii using constructed plasmids as positive controls.

Results: Designed primers and probes allowed molecular detection, in either single or multiplex assays, of agent-specific targets with analytical sensitivities of between 1 and 100 DNA copies. The plasmids could be used as positive controls. False-positive results due to contamination by the positive control were easily detected by sequencing and eliminated by digestion with NotI.

Conclusion: Plasmid A and B can be used as positive controls in molecular assays for the detection of bioterrorism agents in clinical specimens or environmental samples. Plasmid C can be used as a positive control in differentiation of vesicular rashes. It is also possible to avoid or to ensure immediate detection of false positive results due to contamination by positive controls using these plasmids. These plasmids and the corresponding primers and probes are immediately available for all clinical microbiology laboratories provided they have molecular amplification equipment.

Show MeSH
Related in: MedlinePlus