Gram-positive anaerobic cocci (GPAC), including species of the genus Atopobium, are integral members of the human microbiota, colonizing mucosal environments such as the oral cavity, gastrointestinal tract, and female urogenital system [1]. While typically benign and regarded as commensals, these bacteria can transition into opportunistic pathogens under conditions of immune suppression, tissue injury, or microbial dysbiosis 1, 2, 3, 4. Among these, Atopobium vaginae - recently reclassified into the genus Fannyhessea (e.g., F. vaginae, F. massiliense ; [5]) - has garnered attention due to its strong association with bacterial vaginosis (BV; 6, 7, 8). Fannyhessea is described as component of vaginal biofilms, often coexisting with Gardnerella species, serving as a diagnostic marker for BV 8, 9, 10. Genomic studies have revealed substantial heterogeneity within this group, highlighting the need for species-level differentiation in clinical diagnostics and research [10]. Beyond mucosal colonization, Atopobium spp. have been implicated in more invasive infections, including bacteremia and pregnancy-related complications such as sepsis and infected subchorionic hematomas 11, 12, 13. These clinical associations underscore the importance of understanding how these bacteria persist and thrive in host environments.

One critical aspect of bacterial persistence is nutrient acquisition 14, 15, 16. Like other mucosal commensals, Atopobium must compete for limited resources within the host. Major players of the Gram-positive cocci, such as S. aureus and S. pyogene,s are known to deploy a wide array of virulence factors - adhesins, toxins, and immune evasion proteins - to manipulate host defenses 17, 18, 19, 20, 21, 22, 23. GPAC species like F. magna also possess immune-modulating capabilities, including the production of Protein L, Finegoldia adhesion factor (FAF), and the subtilisin-like protease SufA 2, 3, 24, 25; however, little is known about how Atopobium accesses host-derived nutrients. Understanding these metabolic interactions is essential to elucidate how these bacteria maintain colonization and potentially transition to pathogenic states. Tween-80, also known as polysorbate 80 or polyoxyethylene sorbitan monooleate, is a non-ionic surfactant, commonly used as an emulsifier in food products or pharmaceuticals . For S. aureus and Lactobacillus, elevated growth rates and increased biomass were observed in the presence of 0.1% Tween-80 in the medium . Given the increasing recognition of Atopobium in polymicrobial infections [26], a deeper understanding of its interactions with host immune cells and its nutrient sources is warranted.

This exploratory study aims to bridge these knowledge gaps by first investigating how Atopobium spp. utilize host-derived nutrients - particularly serum components such as albumin - to support growth and subsequently examining how these bacteria interact with human neutrophils to modulate immune responses. Together, these insights will contribute to a more comprehensive understanding of the role of Atopobium in microbial dysbiosis and opportunistic infections, with implications for targeted therapeutic strategies.