Recto-Anal Junction (RAJ) and Fecal Microbiomes of Cattle Experimentally Challenged With Escherichia coli O157:H7

Abstract

Cattle are the asymptomatic reservoirs of Escherichia coli O157:H7 (O157) that preferentially colonizes the bovine recto-anal junction (RAJ). Understanding the influence of O157 on the diversity of the RAJ microbiota could give insights into its persistence at the RAJ in cattle. Hence, we compared changes in bovine RAJ and fecal microbiota following O157 challenge under experimental conditions. Cattle were either orally challenged (n = 4) with10 10 CFU of a streptomycin-resistant O157 strain 86-24, or mock-challenged (n = 4) with phosphate buffered saline. Rectoanal mucosal swab (RAMS) and fecal samples were collected at different time points for analysis. Alpha diversity measures (Chao1 species richness and Shannon diversity index) were found to be significantly different between RAMS and fecal samples but not influenced by O157 challenge. The Firmicutes to Bacteroidetes (F: B) ratio was higher in RAMS samples from O157 colonized animals and this may have influenced the consistent yet decreased O157 colonization at the RAJ. Specific bacterial genera that were present in relative low abundance in fecal and RAMS microbiota did not affect overall microbial diversity but were associated with O157 colonization. Differential abundance analysis (DAA) of genera in samples from O157 shedding cattle indicated significantly higher relative abundance of Paenibacillus and Fusobacterium in RAMS, and Tyzzerella in fecal samples. Mockchallenged cattle showed higher relative abundance of Intestinimonas and Citrobacter in RAMS samples, and Succinivibrio, and Prevotella 1 in fecal samples. These results suggest that O157 challenge exerts transient influence on the intestinal microbial community which in turn might promote O157 colonization in a site-specific manner.

Early immune innate hallmarks and microbiome changes across the gut during Escherichia coli O157: H7 infection in cattle

“… 77 , likely due to individual and environment particularities. Of note, despite high dose infective inoculum (10 10 CFU), the abundance of the Escherichia-Shigella taxon did not increase in challenged calves; a phenomenon that was previously reported 77 , 78 .…”

Characterizing the Cattle Gut Microbiome in Farms with a High and Low Prevalence of Shiga Toxin Producing Escherichia coli

“…Higher alpha diversity identified among some STEC shedders has been observed in previous studies in both beef [16,54] and dairy cattle [22]. By contrast, some reports have found that STEC carriage in individual cattle was associated with lower alpha diversity [17,20,23,55].…”

“…Zhao et al (2013), for instance, found that butyrate-producing species were more abundant in low-STECshedding cattle and were critical in avoiding RAJ lesions [17], suggesting the role of certain taxa as "inhibitors" or "promoters" [17]. Contrasting results have been observed among studies, but in general, there is a consensus that STEC shedders have a higher proportion of members from the order Clostridiales, the dominant order found in the bovine gut microbiome [18,[21][22][23][24]54,55,57]. Consistent with other reports, a lower abundance of Proteobacteria was observed in STEC shedders [22,55].…”

“…We also previously showed that microbial communities from patients with acute enteric infections caused by STEC and other pathogens had a lower bacterial richness with an increased abundance of Proteobacteria (genus Escherichia) and decreased abundance of Bacteroidetes compared to healthy communities [14,15]. With regard to cattle, varying results have been observed in the richness and composition of the fecal microbiome between STEC shedders and non-shedders [16][17][18][19][20][21][22][23][24]. Within a specific farm, for example, some studies observed no difference in diversity among STEC shedders and non-shedders [19,21], whereas other studies detected significantly higher [22] and lower [23] diversity in STEC shedders despite controlling for age, farm, and diet.…”

“…With regard to cattle, varying results have been observed in the richness and composition of the fecal microbiome between STEC shedders and non-shedders [16][17][18][19][20][21][22][23][24]. Within a specific farm, for example, some studies observed no difference in diversity among STEC shedders and non-shedders [19,21], whereas other studies detected significantly higher [22] and lower [23] diversity in STEC shedders despite controlling for age, farm, and diet. This lack of consensus among previous reports compels further investigation.…”