Effects of Acute and Chronic Exposure to Residual Level Erythromycin on Human Intestinal Epithelium Cell Permeability and Cytotoxicity

Effect of erythromycin residuals in food on the development of resistance in Streptococcus pneumoniae: an in vivo study in Galleria mellonella

Background

The use of antimicrobials to treat food animals may result in antimicrobial residues in foodstuffs of animal origin. The European Medicines Association (EMA) and World Health Organization (WHO) define safe antimicrobial concentrations in food based on acceptable daily intakes (ADIs). It is unknown if ADI doses of antimicrobials in food could influence the antimicrobial susceptibility of human-associated bacteria.

Objectives

This aim of this study was to evaluate if the consumption of ADI doses of erythromycin could select for erythromycin resistance in a Galleria mellonella model of Streptococcus pneumoniae infection.

Methods

A chronic model of S. pneumoniae infection in G. mellonella larvae was used for the experiment. Inoculation of larvae with S. pneumoniae was followed by injections of erythromycin ADI doses (0.0875 and 0.012 μg/ml according to EMA and WHO, respectively). Isolation of S. pneumoniae colonies was then performed on selective agar plates. Minimum inhibitory concentrations (MICs) of resistant colonies were measured, and whole genome sequencing (WGS) was performed followed by variant calling to determine the genetic modifications.

Results

Exposure to single doses of both EMA and WHO ADI doses of erythromycin resulted in the emergence of erythromycin resistance in S. pneumoniae. Emergent resistance to erythromycin was associated with a mutation in rplA, which codes for the L1 ribosomal protein and has been linked to macrolide resistance in previous studies.

Conclusion

In our in vivo model, even single doses of erythromycin that are classified as acceptable by the WHO and EMA induced significant increases in erythromycin MICs in S. pneumoniae. These results suggest the need to include the induction of antimicrobial resistance (AMR) as a significant criterion for determining ADIs.

Role of ROCK/NF‑κB/AQP8 signaling in ethanol‑induced intestinal epithelial barrier dysfunction

The present study aimed to investigate the signaling pathways and the underlying molecular mechanisms involved in ethanol-induced intestinal epithelial barrier (IEB) dysfunction. Therefore, an in vitro experimental model of IEB was established using an ethanol-treated Caco-2 intestinal epithelial cell monolayer. The results confirmed that Rho-associated kinases (ROCKs), namely ROCK1 and ROCK2, were involved in the underlying pathway of ethanol-induced IEB dysfunction. Ethanol exposure significantly increased the expression of both ROCK isoforms and the activity of nuclear factor κB (NF-κB). Furthermore, ROCK1- and ROCK2-specific small interfering RNAs (siRNAs), and the NF-κB inhibitor ammonium pyrrolidine dithiocarbamate partially inhibited transepithelial electrical resistance in Caco-2 cells in an in vitro IEB model. In addition, ROCK1- and ROCK2-specific siRNAs inhibited the activity of NF-κB, thereby downregulating the expression of aquaporin 8 (AQP8). Taken together, the results of the present study suggested that ROCK1/ROCK2-mediated activation of NF-κB and upregulation of AQP8 expression levels may represent a novel mechanism of ethanol-induced impairment of IEB function.