A complex bacterial microbiota is present in human pathological scars

Purpose: We aimed to convince the fact of bacterial colonization in pathological scars using histopathological observation and 5R 16S sequencing to clarify the correlation between pathological scar formation and bacterial colonization.Methods: A total of 57 patients classified by etiology as ear-piercing, infection-associated, burn, surgery, and traumatism, were respectively enrolled in this study and underwent extensive pathological scars excision in the outpatient department. To determine the presence of bacteria, microbiological culture, immunofluorescence, immunohistochemistry, immunoelectron microscopy and a 16S rDNA-based PCR detection method was applied. Through 16S sequencing results, the microbial composition of pathological scar formed by different injury factors and the correlation between bacterial function prediction and specific clinical features were analyzed.Results: We found that pathological scars of different etiologies have different microbial compositions, and these bacteria were widely distributed in collagen fibers, immune cells and fibroblasts. We noted the association of bacteria or their predictive function with pathological scars' color, aggressive growth, contracture and local tissue hypoxia. We found that burn scars had a richer and more diverse microbiome than all other pathological scars. An average of 91.6 bacterial species were detected in any single burn scar sample, whereas the average was 76.2 in all other pathological scars. Almost all kinds of bacteria were detected in burn scar specimens, including 680 endemic bacteria. In contrast, Clostridiales and Burkholderiales dominated the microbiome of postoperative scars, while Burkholderiales concentrated mainly on infection-associated scars. The gram-negative bacteria dominated in all pathologic scars except those formed by surgery, which was consistent with the positive rate of LPS/LTA immunohistochemical staining.Conclusions: The results of our work provide compelling evidence that bacteria colonize pathological scars. The bacteria in keloid were more pathogenic than the bacteria in hypertrophic scars, and the colonized bacteria had stronger migration ability, which may be the reason for the invasive growth of pathological scars. These findings may lead to a better understanding of its pathogenesis and will also help develop other innovative methods to avoid the growth and regeneration of pathological scars.