D3.529 - Altered Virulence of Pseudomonas aeruginosa from Polystyrene-Fed Zophobas atratus Larvae and Immunological Effects of Microplastics on Murine Lungs

Plastic pollution poses a severe threat, yet Zophobas atratus larvae can biodegrade polystyrene (PS). While mechanical degradation is documented, gut microbiota adaptation remains underexplored. This study aimed to isolate Pseudomonas aeruginosa from PS-fed larvae to determine if biodegradation alters antibiotic resistance and virulence in mice. Additionally, we investigated early pulmonary immunological responses and fibrotic markers following PS microplastic (PS-MP) aspiration.

Z. atratus larvae were fed oatmeal (control) or PS foam for 30 days. P. aeruginosa strains were isolated from gut homogenates and tested for antibiotic sensitivity. To evaluate virulence, BALB/c mice were inoculated via oropharyngeal aspiration with either the wild-type strain (PA^W) or the PS-modified strain (PA^M) at doses ranging from 10⁵ to 10¹⁰ CFU; endpoints included LD50 and lung histology. Separately, mice (n=6/group) received 1.5 µm PS latex microparticles (1.03×10⁷) or saline 3x/week for 21 days. Lung tissues were analyzed for hydroxyproline, histology, macrophage activity, and Nrf2/STAT1 expression.

Larvae in the experimental group actively consumed polystyrene, evidenced by frass deposition and gallery formation, while maintaining normal molting cycles. Microbiological analysis confirmed the presence of P. aeruginosa in the gut homogenates. The PA^M strain demonstrated a slight increase in antibiotic resistance compared to the PA^W. In the in vivo model, the PA^M exhibited lower LD50 values. Histological examination of murine lung tissue infected with these strains revealed severe pneumonia characterized by alveolar destruction, necrosis, hemorrhage, and vascular thrombosis. However, PS-MP-treated mice exhibited significant alveolar macrophage infiltration and robust intra-alveolar particle phagocytosis, indicating an active cellular response. A mild increase in Nrf2 expression suggested early antioxidant activation. In contrast, STAT1 expression was notably decreased in the PS-MP group, strongly suggesting immune dysregulation and increased susceptibility to remodeling processes within the pulmonary system.

PA^M strain exhibits increased virulence and resistance, suggesting unintended microbiological consequences of biodegradation. Crucially, the study reveals that exposure to PS-MP induces immune dysregulation, characterized by suppressed STAT1 signaling despite an active macrophage response. These findings highlight health risks of airborne MP exposure and the need to understand the link between immune response and chronic pulmonary effects to develop mitigation strategies.

The future study will examine both PA^W and PA^M bacterial strains to understand how plastic degradation products and bacterial-plastic interactions contribute to lung pathology and immune response.