Inflammatory modulation and outer membrane vesicles (OMV) production associated to Bacteroides fragilis response to subinhibitory concentrations of metronidazole during experimental infection

Objective: An experimental infection based on a tissue cage model was reproduced to evaluate the interference subinhibitory concentration (SIC) of metronidazole in Bacteroides fragilis OMV production patterns and immunological and histological characteristics of the host facing the experimental challenge. Methods: A tissue cage model was reproduced for B. fragilis experimental challenge in three Wistar rats groups: negative control group (NC) without bacterial inoculation; positive control group (PC) infected with parental strain; and experimental group (EG) infected with the parental strain and treated with metronidazole SIC. Tissue cage sections and histological preparations were evaluated under optical and transmission electron microscope. Observations included OMV identification and count and cellular envelope evaluation. Transcriptional analyses were performed to evaluate cytokines expression levels. Results: Total counts of leukocytes and neutrophils were higher for EG, and slight increase in PC group. It was observed an exacerbated inflammatory infiltrate after 8 days on infection. The expression of TNF-a was increased during the experiments, along with IL-1a and IL-6. MCP-1 levels were suppressed in almost every evaluated time-point. The IL-10 was exacerbated in EG group. A massive production and release of OMV and cell wall thickening were observed especially the EG group. Conclusions: Despite literature data suggest positive association between OMV and antimicrobial stress for Gram negatives, no correlations are made for B. fragilis and drug-response during experimental model of infection. Results corroborate observations in which OMV may be involved in bacterial pathogenicity once the phenomenon was observed along histological evidence of exacerbated inflammation and cytokines modulation. (c) 2021 Elsevier Ltd. All rights reserved.

Automated summary

This study reproduced an experimental infection of Bacteroides fragilis using a tissue cage model to evaluate the subinhibitory concentration (SIC) of metronidazole in OMV production patterns and immunological and histological characteristics. The results showed that in the experimental group, the total counts of leukocytes and neutrophils were higher, and there was an exacerbated inflammatory infiltrate. Additionally, there was a massive production and release of OMV. These results confirm the potential involvement of OMV in the pathogenicity of B. fragilis.