An exploratory study of gut microbiota and humoral immune responses following bacterial ghost administration in rats

The rise of multidrug-resistant pathogens necessitates innovative immunotherapeutic approaches. Bacterial ghosts (BGs) are non-viable empty cell envelopes retaining antigenic determinants, offer a safe and potent immunomodulatory alternative to live bacterial vaccines. This exploratory study examined the selected tolerability parameters, humoral immune responses, and gut microbiota profiles potential of Staphylococcus aureus-derived ghost cells (GCs) in Sprague Dawley rats. Animals received three doses at one-week intervals via oral and intramuscular (IM) administration at low (10⁶ units/mL) and high (10⁹ units/mL) doses over a 21-day period. Hemocompatibility, serum biochemistry, and histopathology of key organs provided preliminary insights into the tolerability of the formulation under the experimental conditions. Serum immunoglobulin profiling revealed increases in GC-specific IgG and IgA levels with oral administration, while IM delivery showed less systemic variations in antibody production. qRT-PCR analyses indicated a minimal but detectable pro-inflammatory cytokine expression, notably TNF-α, especially in high-dose IM groups. Gut microbiome analysis via 16S rRNA sequencing identified differences in microbial diversity indices and the relative abundance of selected bacterial taxa across experimental groups. Histological assessments of gut tissue indicated mild, non-pathological mucosal changes only at high oral doses. Overall, the findings provide preliminary observations on humoral immune responses, selected tolerability parameters, and gut microbiota profiles following GC administration. These preliminary findings encourage further investigation of BGs as engineerable platforms with potential applications in immunomodulation, mucosal vaccine development, and microbiome-targeted interventions.