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    Borrelia burgdorferi ospC Genotyping Using Luminex Technology

    Patrick Pearson, Olivia Skaltsis, Chu-Yuan Luo, Guang Xu, Zachary Oppler, Dustin Brisson, Stephen M Rich

    Published: 2023-09-01 DOI: 10.17504/protocols.io.5jyl899k8v2w/v2
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    Abstract

    Borrelia burgdorferi is an important tickborne human pathogen and can be grouped into separate strains based on the outer surface protein C ( ospC ) gene. The detection and characterization of different ospC genotypes is vital for research on B. burgdorferi and the risk it poses to humans. Here we present a novel, multiplex assay based on Luminex xMAP technology for the detection of B. burgdorferi ospC genotypes. The assay has 5 major steps: amplification of the ospC gene, enzymatic purification, incorporation of biotinylated nucleotides into the template DNA, hybridization to Luminex microspheres, and detection of fluorescent signals corresponding to each ospC genotype. This protocol can be used for the characterization of ospC genotypes in B. burgdorferi infected ticks, reservoir hosts, and/or clinical samples.

    (The last step in this version contains a supplemental video with extra context and tips, as part of the protocols.io Spotlight series, featuring conversations with protocol authors.)

    Before start

    Steps

    PREPARING SOLUTIONS

    1.

    1X xTAG buffer

    1. Add 1 mL of 10X xTAG buffer to 9 mL of molecular grade water. Scale volume up or down as necessary.
    2. Store at 4°C until use
    2.

    Bead mix solution (75 beads/μL)

    The specific Luminex microspheres (beads) are sold in concentrations of 2.5X10^6 beads/mL. The final concentration of a working bead mix solution is 75 beads/μL. For a 96 well plate, make enough bead mix for 115 samples (~1.2X) to account for pipetting error. Scale volume up or down as necessary.

    1. Vortex each bead type (Table 1 from Materials) for at least 20 seconds
    2. Add 69 μL of each bead type to an amber 5 mL tube
    3. The volume with 21 bead types will be 1449 μL
    4. Add 851 μL of 1X xTAG buffer to bring total volume to 2300 μL
    5. Store at 4°C until use
    3.

    ASPE primer mix solution (500 nM)

    1. Dilute ASPE primers (from IDT) to 200 uM

    2. In 2 mL tube, add 947.5 μL of molecular grade water

    3. Add 2.5 μL of each ASPE primer (Table 2 below)

    4. Vortex and store at -20°C until use

    AB
    ospC ALL Tag 12CATAATCAATTTCAACTTTCTACTAGATTAGGCCCTTTAACAGACTCATC
    ospC Type A Tag 14AATTTCTTCTCTTTCTTTCACAATATTGTGATTATTTTCGGTATCC
    ospC Type B Tag 15TACTTCTTTACTACAATTTACAACCTCGTTGCGATTTGCTTCA
    ospC Types E/C Tag 72CTATCATTTATCTCTTTCTCAATTTGCAAGTAAGGTCTCAACTT
    ospC Types I/C Tag 22CAAACAAACATTCAAATATCAATCTCCGTTGTTATCTGCCTCATTATCT
    ospC Type D Tag 18ACACTTATCTTTCAATTCAATTACATGATTATTTAGAGTGCCTAAAGCATTGTTTTGATC
    ospC Type E Tag 36ATTAAACAACTCTTAACTACACAATGTGTTTTTACTCTGATTGGCCTCTAAACCATTATTGCC
    ospC Type F Tag 42CACTACACATTTATCATAACAAATCGCCTGAACGCCTAAACCATTTGCATC
    ospC Type G Tag 44TCATCACTTTCTTTACTTTACATTGGTGTTGTGATTCGCATCAG
    ospC Type H Tag 46TTAAACAATCTACTATTCAATCACGCCCCCATCGTCACCCAAAGTGCCATTTTG
    ospC Type I Tag 48AATCAACACACAATAACATTCATATTTGAAATTAAATATGCTCCTGA
    ospC Type J Tag 52TTCTTCATTAACTTCTAATCTTACTCCGTTTTGACCCACTTCAGC
    ospC Type K Tag 20CTTTCTCATACTTTCAACTAATTTCCCCGCTTCGACAGCTAAACCACCATTTTGTTG
    ospC Type L Tag 54TTAATACAATTCTCTCTTTCTCTAATCGCTACCTAAAGTACCACCTGCTTC
    ospC Type M Tag 30CTTAACATTTAACTTCTATAACACACCGGCATTTAAACCATTTTGGGCTATCAAA
    ospC Type N Tag 56CTTAAACTCTACTTACTTCTAATTGTTTTGCACATCATCTAAACCATTATTATT
    ospC Type O Tag 61AATCTCTACAATTTCTCTCTAATATTGGTTAACTAAGCCATTTGCC
    ospC Type T Tag 38ATTCAATACTATCTAACACTTACTATGGCCTGCATCGACACT
    ospC Type U Tag 63CTAAATCACATACTTAACAACAAACTGCCCTTGCAAGTCCTGT
    ospC Type V Tag 65TACTTAAACATACAAACTTACTCAGAGCCGCTTGAGCAGTTAAACCATTTGCACC
    ospC Type W Tag 67ATCTCAATTACAATAACACACAAATCGTTTCGATTTGCTTCTACACCC

    Table 2: ASPE Primers

    4.

    ASPE dNTP Mix (50 μM)

    Before making this solution, dilute the dTTP, dCTP, and dGTP (NEB) from 100 mM to 10 mM, and discard the dATP

    1. In 2 mL tube, add 430 μL of molecular grade water
    2. Add 2.5 μL of each 10 mM dTTP, dCTP, and dGTP
    3. Add 62.5 μL of 0.4 mM biotin-14-dATP
    4. Vortex and store at -20°C until use
    5.

    Streptavidin, R-phycoerythrin conjugate (SAPE) solution

    The SAPE is supplied as 1 mg/mL solution. Dilute SAPE to 10 μg/mL in 1X xTAG buffer. For a 96 well plate, make enough SAPE solution for 116 samples (~1.2X). Scale up or down as necessary.

    1. In a 15 mL tube, aliquot 87 μL SAPE into 8613 μL 1X xTAG buffer
    2. Total volume is 8700 μL
    3. Make fresh immediately before use in step 12 below

    NESTED PCR

    6.

    Note: Every batch of samples must have three no template controls (NTCs) included at the nested PCR step. They are used to determine positive ospC genotypes after analysis on the MAGPIX instrument, and to confirm that no contamination occurred during the assay.

    First round PCR

    Master mix preparation

    1. Prepare master mix according to Table 4 below for each sample. Scale up depending on the sample size
    2. Add master mix components to a tube, vortex, and store on ice
    AB
    PrimerSequence (5'-3')
    ospC1FATGAAAAAGAATACATTAAGTGCA
    ospC622RCTTGGACTTTCTGCCACAACA

    Table 3: First round nested PCR primers

    AB
    ComponentVolume (μL)
    Promega PCR Master Mix (2X)12.5
    ospC1F (10 uM)0.5
    ospC622RC (10 uM)0.5
    Molecular grade water10.5

    Table 4: First round PCR master mix

    Loading master mix and template DNA

    1. Aliquot 24 μL of the master mix into a well for each sample
    2. Aliquot 1 μL of template DNA or NTC
    3. Seal wells firmly with cap strips
    4. Vortex and centrifuge plate at 2500 RPM for 1 minute
    5. Load plate into thermal cycler and run program in Table 5 (step 7)
    7.

    Nested PCR Program

    ABC
    Temperature (°C)TimeCycles
    952 minutes1
    9530 seconds32
    4930 seconds32
    7250 seconds32
    7210 minutes1
    4Hold1

    Table 5: Nested PCR program

    8.

    Second Round PCR

    Master mix preparation

    1. Prepare master mix according to Table 7 below for each sample. Scale up depending on the sample size
    2. Add master mix components to a tube, vortex, and store on ice
    AB
    PrimerSequence (5'-3')
    OC6(+)24AAAGAATACATTAAGTGCGATATT
    OC602(-)22GGGCTTGTAAGCTCTTTAACTG

    Table 6: Second round nested PCR primers

    AB
    ComponentVolume μL
    Promega PCR Master Mix (2X)12.5
    OC6(+)24 (10 μM)0.5
    OC602(-)22 (10 μM)0.5
    Molecular grade water10.0

    Table 7: Second round PCR master mix

    Loading master mix and template DNA

    1. Aliquot 23.5 μL of the master mix into a well for each sample
    2. Add 1.5 μL of the DNA template or NTC from the first round PCR into the correct well
    3. Seal wells firmly with cap strips
    4. Vortex and centrifuge plate at 2500 RPM for 1 minute
    5. Load plate into thermal cycler and run program in Table 5 (step 7)

    EXOSAP-IT

    9.

    Aliquot 7.5 μL of amplified DNA into wells on a new plate1. Add 3 μL of ExoSAP-IT to each well

    1. Seal wells firmly with cap strips
    2. Vortex and centrifuge plate at 2500 RPM for 1 minute
    3. Load plate into thermal cycler and run program in Table 8
    ABC
    Temperature (°C)Time (minutes)Cycles
    37151
    80151
    4Hold1

    Table 8: ExoSAP-IT program

    ALLELE SPECIFIC PRIMER EXTENSION (ASPE)

    10.

    Master mix preparation

    1. Prepare master mix according to Table 9 below for each sample. Scale up depending on the sample size
    2. Add master mix components to a tube, vortex, and store on ice
    AB
    ComponentVolume (μL)
    Molecular grade water9.75
    10X NEB PCR buffer2
    ASPE primer mix (500 nM)2
    ASPE dNTP mix (50 μM)1
    NEB Taq polymerase (5 U/μL)0.25

    Table 9: ASPE master mix

    1. Aliquot 15 μL of the ASPE master mix into wells on a new plate
    2. Aliquot 5 μL of the amplicon treated product (from step 9) into the correct wells
    3. Seal wells firmly with cap strips
    4. Vortex and centrifuge plate at 2500 RPM for 1 minute
    5. Load plate into thermal cycler and run program in Table 10
    ABC
    Temperature (°C)TimeCycles
    952 minutes1
    9530 seconds35
    5630 seconds35
    6830 seconds35
    685 minutes1
    4Hold1

    Table 10: ASPE program

    BEAD HYBRIDIZATION

    11.

    Vortex bead mix for at least 30 seconds1. Aliquot 20 μL of bead mix into wells on a new plate

    1. Aliquot 3.5 μL of the ASPE product (from step 10) into the correct wells
    2. Gently pipette up and down several times to mix
    3. Seal wells firmly with cap strips
    4. Load plate into thermal cycler and run program in Table 11
    ABC
    Temperature (°C)Time (minutes)Cycles
    9621
    37301

    Table 11: Bead hybridization program

    ANALYSIS ON MAGPIX

    12.

    Addition of SAPE (reporter solution)

    1. Invert SAPE (10 μg/mL) several times and pour into 25 mL reservoir
    2. Aliquot 75 μL SAPE solution to every well
    3. Gently pipette up and down several times to mix
    4. Transfer samples to pre-warmed heater block (37°C) on MAGPIX instrument
    5. Incubate at 37°C for 15 minutes
    13.

    Analyze samples on MAGPIX

    Please refer to Luminex technical support and the MAGPIX manual for detailed instructions on how to create a protocol, run a batch of samples, and MAGPIX maintenance. Specific settings for our ospC genotyping protocol are listed below.

    1. 70 μL sample volume
    2. Sample wash "on"
    3. Heater set at 37°C
    4. 50 bead count minimum

    DATA ANALYSIS

    14.

    At the end of the run, a .csv file will be created containing the protocol/run information and the raw median fluorescent intensity (MFI) results for each sample

    1. Open the .csv file in Microsoft Excel
    2. Copy the "DataType: Median" results for the three NTCs and every sample to a new sheet in the workbook
    3. Using the three NTCs, calculate the average background MFI value for every ospC genotype (analyte)
    4. Add three standard deviations to the averages. These values (NTC values) are specific for each genotype. NTC values are determined for each genotype, since background can vary slightly between genotypes.
    5. For individual samples, raw ospC genotype MFI values that have a ratio to NTC value (RNTC) of ≥ 3 are considered positive

    Example

    1. For ospC genotype A the MFI values in the three NTCs were (100, 125, and 150)
    2. The average (125) plus three standard deviations (20.4) is 186 (NTC value)
    3. The raw MFI value for ospC genotype A in sample "X" is 800
    4. Sample "X" is positive for ospC genotype A since the RNTC value is 4.3

    Spotlight video

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