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Son et al. Microbiome Res Rep. 2025;4:29 https://dx.doi.org/10.20517/mrr.2025.14 Page 9 of 19

In the jejunum, mucosa-associated microbiota are more directly relevant to intestinal health than luminal
microbiota, primarily due to their interaction with enterocyte PRRs. Mucosa-associated microbiota are in
close contact with epithelial cells and influence the intestinal immune system, whereas luminal microbiota
[80]
interact less directly with epithelial cells and primarily affect the digesta . Furthermore, the composition of
mucosa-associated microbiota differs from that of luminal microbiota. Recent studies have emphasized the
distinction between these two microbial populations due to differing environmental characteristics in the
lumen and mucosa, such as pH and oxygen levels [9,23,81] . Luminal microbiota are more sensitive to dietary
changes and environmental fluctuations than mucosa-associated microbiota. For instance, the pH in the
jejunal lumen is more variable due to the influence of intestinal secretions like bile acids, while the pH at the
mucosal surface is relatively stable to protect epithelial tissues. Oxygen levels also differ, with higher oxygen
[82]
concentrations near the mucosa due to vascularization . As a result, luminal microbiota are mainly
anaerobic, whereas mucosa-associated microbiota are more often aerobic [83,84] . Given these characteristics,
the jejunal mucosa-associated microbiota serve as a valuable indicator for evaluating intestinal health in
pigs.

IMPACTS OF F18 E. coli CHALLENGE ON THE JEJUNAL MUCOSA-ASSOCIATED
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MICROBIOTA
As mentioned previously, the intestinal microbiota interacts with intestinal cells in pigs both directly and
indirectly. The composition of the jejunal mucosa-associated microbiota serves as an important indicator of
+
intestinal health in pigs. Data from eight studies investigating the impact of F18 E. coli challenge on the
jejunal mucosa-associated microbiota were analyzed, summarizing changes in relative abundance (RA) at
the phylum, family, genus, and species levels [Table 3] [9,23,27-30,36,37] . Literature was retrieved from PubMed and
Google Scholar using keywords such as F18 E. coli, challenge, PWD, mucosa-associated microbiota,
+
intestinal health, jejunum, and nursery pigs. The studies were manually screened based on their
experimental procedures. For consistency, only studies involving both negative control (NC) and positive
control groups, and using nursery pigs, were included. Data derived from jejunal digesta were excluded.
Only results showing statistically significant changes are presented.

The F18 E. coli challenge negatively affects the composition of the jejunal mucosa-associated microbiota in
+
two major ways. First, it increases the RA of harmful bacteria within the jejunal mucosa, many of which are
pathogenic or promote inflammation. For instance, increased RA of Helicobacteraceae and Helicobacter was
observed in studies using the F18 E. coli challenge model [23,36] . These taxa are associated with subclinical
+
inflammation . The inoculation also led to increased RA of Pseudomonadaceae , a family that includes
[23]
[85]
Pseudomonas aeruginosa, an opportunistic pathogen detrimental to intestinal health . Additionally, an
[86]
increase in Eubacterium RA was reported , which may raise disease susceptibility, as certain species of
[28]
Eubacterium are considered disease markers and potential opportunistic pathogens [87,88] . An elevated RA of
Terrisporobacter was also noted, and this genus has been correlated with C-reactive protein, a well-known
marker of inflammation .
[89]
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Second, F18 E. coli reduces the RA of beneficial bacteria, contributing to dysbiosis. In one study, pigs
challenged with F18 E. coli showed a decreased RA of Lactobacillus and Bifidobacterium, which are known
+
[27]
to produce lactic acid and short-chain fatty acids (SCFA) . Gormley et al. reported that RA of Bacillus and
Corynebacterium, both of which help reduce oxidative stress and produce SCFA, was lower in challenged
pigs compared to NC pigs . Similarly, F18 E. coli appeared to reduce the RA of Mitsuokella, a genus
+
[28]
capable of producing SCFA from phytate degradation [36,90] . RA of Megasphaera, which converts lactic acid
into SCFAs and competes with lactic-acid-consuming harmful bacteria, was also reduced [91,92] . A decrease in
[36]
Prevotellaceae RA was reported , and at the species level, RA of Prevotella copri, a fiber-fermenting and