Enteric dysbiosis promotes antibiotic-resistant bacterial infection: systemic dissemination of resistant and commensal bacteria through epithelial transcytosis

Abstract

Antibiotic usage promotes intestinal colonization of antibiotic-resistant bacteria. However, whether resistant bacteria gain dominance in enteric microflora or disseminate to extraintestinal viscera remains unclear. Our aim was to investigate temporal diversity changes in microbiota and transepithelial routes of bacterial translocation after antibiotic-resistant enterobacterial colonization. Mice drinking water with or without antibiotics were intragastrically gavaged with ampicillin-resistant (Amp-r) nonpathogenic Escherichia coli (E. coli) and given normal water afterward. The composition and spatial distribution of intestinal bacteria were evaluated using 16S rDNA sequencing and fluorescence in situ hybridization. Bacterial endocytosis in epithelial cells was examined using gentamicin resistance assay and transmission electromicroscopy. Paracellular permeability was assessed by tight junctional immunostaining and measured by tissue conductance and luminal-to-serosal dextran fluxes. Our results showed that antibiotic treatment enabled intestinal colonization and transient dominance of orally acquired Amp-r E. coli in mice. The colonized Amp-r E. coli peaked on day 3 postinoculation and was competed out after 1 wk, as evidenced by the recovery of commensals, such as Escherichia, Bacteroides, Lachnospiraceae, Clostridium, and Lactobacillus. Mucosal penetration and extraintestinal dissemination of exogenous and endogenous enterobacteria were correlated with abnormal epithelial transcytosis but uncoupled with paracellular tight junctional damage. In conclusion, antibiotic-induced enteric dysbiosis predisposes to exogenous infection and causes systemic dissemination of both antibiotic-resistant and commensal enterobacteria through transcytotic routes across epithelial layers. These results may help explain the susceptibility to sepsis in antibiotic-resistant enteric bacterial infection.

Commensal bacterial internalization by epithelial cells: An alternative portal for gut leakiness

“…In our model, antibiotic treatment enabled intestinal colonization and transient dominance of orally acquired, antibiotic-resistant E. coli in mice. 16 Moreover, colonization by resistant E. coli was mainly detected in the large intestine and paralleled abnormal bacterial endocytosis (by both resistant bacteria and commensals) by colonocytes. 16 Colonization by antibiotic-resistant E. coli was associated with increased proinflammatory cytokine production in the gut mucosa and bacterial translocation to liver and spleen, but no sign of TJ damage was seen in any intestinal segments.…”

“…16 Moreover, colonization by resistant E. coli was mainly detected in the large intestine and paralleled abnormal bacterial endocytosis (by both resistant bacteria and commensals) by colonocytes. 16 Colonization by antibiotic-resistant E. coli was associated with increased proinflammatory cytokine production in the gut mucosa and bacterial translocation to liver and spleen, but no sign of TJ damage was seen in any intestinal segments. 16 The tissue conductance, macromolecular permeability, and occludin and ZO-1 expression in jejunum, cecum, and colon after colonization of resistant E.coli were comparable to those without infection.…”

“…Herein, such cell culture and animal models with bacterial endocytosis in absence of TJ damage are described. 15,16,38 The actual mechanism of bacterial transcytosis was largely unclear until an elegant study, conducted by Clark et al in 2005, described how low concentrations of IFNg induced the transcellular influx of nonpathogenic, noninvasive bacteria into human Caco-2 cells. 38 In this study, low dose IFNg did not alter cell viability nor affected the transepithelial electrical resistance (TER) and TJ protein expression in the monolayer.…”

“…Two models with enteric bacterial dysbiosis (changes in numbers or composition of gut microbiota) were established, including bowel obstruction 15,29,57 and infection with antibiotic-resistant enterobacteria. 16 The bowel obstruction model induced commensal bacterial overgrowth after loop ligation in the distal small intestine. Bacterial endocytosis by epithelial cells was observed after 6 h of obstruction, whereas TJ damage was seen only after 24 h. 15,29,57 The TJ damage in gut tissues after 24 h of obstruction was evidenced by occludin cleavage, ZO-1 destruction, and increased tissue conductance and macromolecular permeability.…”

“…2,3 Abnormal bacterial adherence and internalization by epithelial cells has been reported in patients and experimental models with colorectal cancers, [4][5][6] inflammatory bowel disease (IBD), 7,8 celiac disease, 9,10 chronic psychological stress, 11,12 surgical manipulation, 13 intestinal obstruction, 14,15 and antibiotic-resistant bacterial infection. 16 Recent evidence suggests that mucosa-associated bacteria may contribute to pathological phenomena since many exhibit adherent and invasive characteristics, and are therefore termed 'pathobionts' (a commensal with the potential to cause disease; see review papers elsewhere). 17,18 However, from the host's point of view, epithelial barrier dysfunction is an indispensable factor underlying the process of bacterial influx, irrespective of their commensal origins or pathogenic properties.…”