[Evaluation of Chlamydia muridarum and mixed bacteria-induced chronic salpingitis models and optimization of mixed...

Chronic salpingitis is an important cause of secondary infertility, tubal pregnancy, and chronic pelvic pain in women. Its pathological characteristics mainly include adhesion of the tubal mucosa, impaired ciliary motility, and luminal occlusion. Due to the difficulty in obtaining human biopsy tissues, establishing a stable, standardized animal model consistent with the pathological progression in humans is of great academic significance for investigating the pathogenesis of chronic salpingitis and screening therapeutic drugs. Currently, there is still a lack of unified, reliable, and cost-effective animal model for chronic salpingitis. This study aims to evaluate the effects of Chlamydia muridarum (CM) and mixed bacteria (MB) in inducing chronic salpingitis in SD rats and to optimize the parameters for MB modeling.

The study consisted of 2 stages: pathogen model comparison and MB dose-effect evaluation. For pathogen model comparison, 30 SPF female SD rats were randomly divided into a control (CON) group, a CM group [inoculation concentration 2×107 inclusion forming units (IFU)/mL], and an MB group [inoculation concentration 3×10⁹ colony forming units (CFU)/mL]. A reproductive tract inoculation method was used to establish the model. Hematoxylin-eosin (HE) staining and transmission electron microscopy (TEM) were performed on days 1, 7, 14, 21, and 28 after modeling to observe pathological morphology of the fallopian tube and ultrastructural changes in epithelial cilia and mitochondria. For MB dose-effect evaluation, 30 specific pathogen free female SD rats were divided into a normal group, a low-dose MB group (3×10¹⁰ CFU/mL), and a high-dose MB group (3×10¹¹ CFU/mL). Serum tumor necrosis factor-α (TNF-α) levels were measured on days 7 and 14 after modeling using enzyme-linked immunosorbent assay (ELISA). Combined with histomorphological scoring under microscopy, inflammation severity was quantitatively evaluated.

Both the CM group and MB group successfully induced typical manifestations of chronic salpingitis. Light microscopy showed interstitial edema of the fallopian tube, thickening of the tubal wall, and marked infiltration of lymphocytes and plasma cells. Under TEM, rats in the modeling groups exhibited characteristic organelle damage, including disordered ciliary arrangement, extensive ciliary collapse and shedding, indistinct axoneme structure, and significant mitochondrial swelling with cristae disruption or disappearance and vacuolar degeneration in the cytoplasm. Time-course comparison showed that on day 7 after modeling, the MB group exhibited a more pronounced inflammatory response than the CM group, characterized by increased neutrophil infiltration. Dose-effect analysis demonstrated that on day 14 after modeling, serum TNF-α levels were significantly elevated in the high-dose MB group (P<0.01), accompanied by aggravated fallopian tube tissue damage with typical chronic inflammatory changes.

Both CM and MB models can effectively simulate the complete pathological process of chronic salpingitis in humans, from acute inflammatory response to chronic fibrosis, with relatively high success rates. However, the CM model requires stringent pathogen culture conditions, higher purchase and maintenance costs, and a longer experimental cycle. In contrast, the MB model uses mixed bacterial strains that are easier to obtain and less costly to prepare. This study confirmed that the MB protocol constructed at a concentration of 3×10¹¹ CFU/mL can stably induce morphological changes consistent with chronic inflammation in rats, and the expression of inflammatory factors shows good quantifiability and reproducibility. This model provides a standardized experimental platform with important academic value for basic research, clinical drug screening, and translational studies of chronic salpingitis.