Nasopharyngeal and oral microbiota profiling in SARS-CoV-2 infected pregnant women

Variations have been found in the upper respiratory tract microbiota in SARS-CoV-2 positive patients compared to healthy subjects, with different dominant species and diversity indexes detected, including a decrease in biodiversity and an increased abundance of bacterial pathogens. Moreover, these discrepancies were observed in patients with both mild and severe symptoms. Notably, the inflammatory state appears to be significantly influenced by the characteristics of the indigenous microbiota. This is particularly interesting in pregnant patients, as pregnancy involves an adaptive adjustment of the microbiota due to hormonal changes aimed at providing immune protection. The relationship between the microbiota of pregnant women and SARS-CoV-2 has not been deeply explored so far. The purpose of the present study is to investigate the relationship between SARS-CoV-2, nasopharyngeal and oral microbiota, and pregnancy. To our knowledge this is the first simultaneous investigation on both nasopharyngeal and oral microbiota in SARS-Cov-2 infected pregnant women. In this study, the nasopharyngeal and oral microbiota were analysed in 43 women in their third trimester of pregnancy enrolled from April 2020 to February 2021. The differential abundance of taxa was tested and alpha and beta diversity were evaluated. SARS-CoV-2 infected pregnant women showed an alteration of the nasopharyngeal and oral microbiota compared to healthy pregnant women. In both the nasopharyngeal and oral microbiota of the SARS-CoV-2 infected pregnant women, we found a variation in taxa, represented by an enrichment of pathobionts, which increased particularly with the severity of symptoms. Specifically, a significant reduction in microbial biodiversity has been identified within the nasopharyngeal microbiota of SARS-CoV-2 positive women. Furthermore, enrichment in pathobionts was noted in both asymptomatic and symptomatic women, with these changes being more pronounced in the nasopharyngeal microbiota compared to the oral one. The nasopharyngeal microbiota of asymptomatic and symptomatic SARS-CoV-2 infected women showed an enrichment of pathogens and pathobionts such as Corynebacterium, Fusobacterium, Neisseria, Streptococcus, Haemophilus, Mycobacterium and Porphyromonas compared with the control group. The oral microbiota showed an enrichment of pathobionts such as Neisseria, Fusobacterium and Streptococcus. A random forest classifier applied to metagenomic data from nasopharyngeal and oral swabs showed that the nasopharyngeal microbiota is the best sampling site to predict the patients’ SARS-CoV-2 infection status. Gulbenkiania, Burkholderia and Actinomyces, all taxa significantly enriched in the control group compared to SARS-CoV-2 infected women, were the most important features selected by the classifier. Finally, correlations between the nasopharyngeal and oral microbiota and clinical parameters of pregnant women, particularly BMI and procalcitonin, were observed. SARS-CoV-2 infected pregnant women showed an alteration of the nasopharyngeal and oral microbiota compared to healthy pregnant women. We found a variation in taxa, represented by the enrichment of pathobionts in both the nasopharyngeal and oral microbiota of SARS-CoV-2 infected pregnant women, particularly increased in symptomatic individuals. The nasopharyngeal microbiota appears to be a better predictor of SARS-CoV-2 infection and its severity than the oral microbiota.