Abstract
ObjectiveGroup B Streptococcus (GBS) is a leading cause of neonatal meningitis and sepsis worldwide. Intrapartum antibiotics given to women carrying GBS are an effective means of reducing disease in the first week of life. Rapid and reliable tests are needed to accurately identify GBS from these women for timely intrapartum antibiotic administration to prevent neonatal disease. Many laboratories now use matrix-assisted laser desorption ionisation time-of-flight mass spectrometry (MALDI-TOF MS) by direct plating or cell lysis for the identification of GBS isolates. The cell lysis step increases time to results for clinical samples and is more complex to perform. Therefore, we seek to evaluate the sensitivity and specificity of the quicker and more rapid direct plating method in identifying GBS.ResultsWe directly compared swab isolates analysed by both direct plating and cell lysis method and demonstrated that direct plating has a sensitivity and specificity of 0.97 and 1, respectively, compared to an additional cell lysis step. We demonstrated that MALDI-TOF MS can be successfully used for batch processing by the direct plating method which saves time. These results are reassuring for laboratories worldwide who seek to identify GBS from swabs samples as quickly as possible.
Highlights
ResultsWe directly compared swab isolates analysed by both direct plating and cell lysis method and demonstrated that direct plating has a sensitivity and specificity of 0.97 and 1, respectively, compared to an additional cell lysis step
Group B Streptococcus (GBS or Streptococcus agalactiae) is a Gram-positive bacterium found colonising in the genitourinary and gastrointestinal tracts of approximately 20% of pregnant women [1–3]
We demonstrated that MALDI-TOF MS can be successfully used for batch processing by the direct plating method which saves time
Summary
MALDI‐TOF MS sample preparation methods We compared the direct plating method against a cell lysis method for MALDI-TOF MS analysis on 96 colonies that exhibit similar morphologies to GBS on CHROMagar from a sub-set of 33 clinically diverse swabs collected from mother-infant pairs. Identification of GBS using CHROMagar and direct plating MALDI‐TOF MS method We analysed 851 rectovaginal, rectal and nasopharyngeal swabs from 155 mother-infant pairs using the direct plating method for MALDI-TOF MS analysis These swabs had initially been identified as GBS positive by Columbia blood agar and confirmed using MALDI-TOF MS by direct plating. The nine discordant samples had similar colony morphologies, with different colouration in some cases, to GBS on CHROMagar (Fig. 1) and were identified as GBS by the direct plating method on MALDI-TOF MS These discrepant strains were subsequently re-analysed by API biochemical test strip kits and MALDI-TOF MS by cell lysis method as previously described [10], and were confirmed as Weissella confusa (n = 4), Streptococcus salivarius (n = 2), Aerococcus viridans (n = 2) and Enterococcus faecalis (n = 1)
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