Abstract
ObjectivePregnant women with bacterial vaginosis due to Gardnerella vaginalis (GV) infection presents with a wide-ranging disease symptomatology. We speculate this may be due to interaction that varies between host immune response and the pathogen. We studied the oxidative burst in polymorphonuclear leukocytes (PMNL)s from maternal blood (MB) and cord blood (CB) upon phagocytosis of GV and compared against E. coli and Group B Streptococcus (GBS).ResultsThe PHAGOBURST™ assay detects fluorescence from oxidized dihydrorhodamine during oxidative burst. The average percentage of PMNL showing oxidative burst was almost two-fold greater with GBS (99.5%) and E. coli (98.2%) than GV (56.9%) (p < 0.01) in MB, but a similar proportion of PMNL with burst activity was seen in CB (84.7%). The mean fluorescence intensity (MFI) of oxidative burst in MB PMNL with GV was lower compared to E. coli but comparable to GBS. The MFI of CB PMNL (1580 ± 245.8) was significantly higher than MB PMNL (1198 ± 262.1) with GV, p = 0.031. The live-cell imaging showed neutrophil oxidative burst upon phagocytosis of GV produces hypochlorous acid (HOCl). Overall, the HOCL-mediated microbicidal activity against GV is more variable and less robust than E. coli and GBS, especially in maternal than CB PMNL.
Highlights
Gardnerella vaginalis (GV) is a vaginal commensal commonly isolated in women of reproductive age
The proportion of polymorphonuclear leukocytes (PMNL) in cord blood (CB) showing oxidative burst when challenged with the three bacterial species, was similar with E. coli (97.7%) and Group B Streptococcus (GBS) (97.5%) but lower with GV (84.7%) but the difference was not statistically significant
With regards to the intensity of oxidative burst, maternal blood (MB) PMNL when stimulated by GV had significantly lower mean fluorescence intensity (MFI) (1026 ± 176) than with E. coli, MFI (1717 ± 220.6)
Summary
Gardnerella vaginalis (GV) is a vaginal commensal commonly isolated in women of reproductive age. It is recognised as a prevalent organism responsible for bacterial vaginosis (BV) [1]. Our study sought if variability in the BV spectrum of disease among pregnant women and neonatal outcomes could be attributed to the innate host immune response during phagocytosis. Our results showed a variable and modest oxidative burst especially when PMNL from maternal blood (MB) phagocytosed GV compared to E. coli and GBS. Columbia Blood Agar with sheep blood medium (Thermo Scientific, Melaka, Malaysia) was used for subculturing of GV and GBS, and plates were incubated in 5% CO2 at 37 °C. The opsonisation of GV and GBS utilised the serum from the corresponding MB or CB samples
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