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Specific Magnetic Bead–Based Capture of Genomic DNA from Clinical Samples: Application to the Detection of Group B Streptococci in Vaginal/Anal Swabs

¹ Centre de Recherche en Infectiologie de l’Université Laval, Centre Hospitalier Universitaire de Québec (Pavillon CHUL), Québec, Canada.

^aAddress correspondence to this author at: Centre de Recherche en Infectiologie de l’Université Laval, Centre Hospitalier Universitaire de Québec (Pavillon CHUL), Sainte-Foy, Québec, Canada, G1V 4G2. Fax 1-418-654-2715; e-mail Michel.G.Bergeron{at}crchul.ulaval.ca.

Background: Group B streptococci (GBS) are a leading cause of sepsis and meningitis in newborns. We previously developed a rapid diagnostic system for GBS detection from vaginal/anal samples obtained from pregnant women during delivery. To facilitate the adaptation of this method for point-of-care testing, we have developed a specific and efficient GBS DNA capture method that is compatible with both PCR and nonamplification detection technologies.

Methods: Superparamagnetic beads were functionalized with oligonucleotide capture probes of different lengths and used to capture GBS genomic DNA (gDNA). A rapid extraction procedure was used to provide DNA from GBS cultures or vaginal/anal samples with added GBS. Hybridization reactions consisting of functionalized beads and target DNA in 30 µL of hybridization buffer were performed for 1 h at room temperature, followed by washing and resuspension in water. Captured DNA was then detected using quantitative PCR.

Results: A 25-mer capture probe allowed detection of 1000 genome copies of purified GBS DNA. The ability to detect GBS was improved by use of a 50-mer (100 copies) and a 70-mer capture probe (10 copies). Detection of approximately 1250 CFU/mL was achieved for diluted GBS broth culture and for vaginal/anal swab samples with added GBS.

Conclusion: Oligonucleotide-functionalized superparamagnetic microbeads efficiently capture GBS gDNA from both bacterial cultures and vaginal/anal samples with added GBS. Efficiency of gDNA capture increases with oligonucleotide length. This technology could be combined with sample preparation and detection technologies in a microfluidic system to allow point-of-care testing for GBS.

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