Loop-mediated isothermal amplification assay for rapid detection of Streptococcus agalactiae (group B streptococcus) in vaginal swabs - a proof of concept study

• Published in: Journal of medical microbiology Vol. 66; no. 3; pp. 294 - 300
• Main Authors: McKenna, James Patrick, Cox, Ciara, Fairley, Derek John, Burke, Rachael, Shields, Michael D, Watt, Alison, Coyle, Peter Valentine
• Format: Journal Article
• Language: English
• Published: England 01.03.2017
• Subjects: Antigens, Bacterial - genetics; Data Accuracy; DNA Primers; Female; Genome, Bacterial; Humans; Nucleic Acid Amplification Techniques - methods; Point-of-Care Systems; Real-Time Polymerase Chain Reaction - methods; Sensitivity and Specificity; Streptococcal Infections - diagnosis; Streptococcal Infections - microbiology; Streptococcus agalactiae - genetics; Streptococcus agalactiae - isolation & purification; Temperature; Vagina - microbiology
• ISSN: 0022-2615; 1473-5644
• DOI: 10.1099/jmm.0.000437

Neonatal sepsis caused by Streptococcus agalactiae [group B streptococcus (GBS)] is a life-threatening condition, which is preventable if colonized mothers are identified and given antibiotic prophylaxis during labour. Conventional culture is time consuming and unreliable, and many available non-culture diagnostics are too complex to implement routinely at point of care. Loop-mediated isothermal amplification (LAMP) is a method that, enables the rapid and specific detection of target nucleic acid sequences in clinical materials without the requirement for extensive sample preparation. A prototype LAMP assay targeting GBS sip gene is described. The assay was 100 % specific for GBS, with a limit of detection of 14 genome copies per reaction. The clinical utility of the LAMP assay for rapid direct molecular detection of GBS was determined by testing a total of 157 vaginal swabs with minimal sample processing using a rapid lysis solution. Compared to a reference quantitative real-time PCR assay, the direct LAMP protocol had a sensitivity and specificity of 95.4 and 100 %, respectively, with positive and negative predictive values of 100 and 98.3 %, respectively. Positive and negative likelihood ratios were infinity and 0.05, respectively. The direct LAMP method required a mean time of 45 min from the receipt of a swab to generation of a confirmed result, compared to 2 h 30 min for the reference quantitative real-time PCR test. The direct LAMP protocol described is easy to perform, facilitating rapid and accurate detection of GBS in vaginal swabs. This test has a potential for use at point of care.