Effects of Administration of Live or Inactivated Virulent Rhodococccus equi and Age on the Fecal Microbiome of Neonatal Foals

Abstract

Background Rhodococcus equi is an important pathogen of foals. Enteral administration of live, virulent R. equi during early life has been documented to protect against subsequent intrabronchial challenge with R. equi, indicating that enteral mucosal immunization may be protective. Evidence exists that mucosal immune responses develop against both live and inactivated micro-organisms. The extent to which live or inactivated R. equi might alter the intestinal microbiome of foals is unknown. This is an important question because the intestinal microbiome of neonates of other species is known to change over time and to influence host development. To our knowledge, changes in the intestinal microbiome of foals during early life have not been reported. Thus, the purpose of this study was to determine whether age (during the first month of life) or administration of either live virulent R. equi (at a dose reported to protect foals against subsequent intrabronchial challenge, viz., 1×1010 colony forming units [CFU]) or inactivated virulent R. equi (at higher doses, viz., 2×1010 and 1×1011 [CFU]) altered the fecal microbiome of foals.Methodology/Principal FindingsFecal swab samples from 42 healthy foals after vaccination with low-dose inactivated R. equi (n = 9), high-dose inactivated R. equi (n = 10), live R. equi (n = 6), control with cholera toxin B (CTB, n = 9), and control without CTB (n = 8) were evaluated by 454-pyrosequencing of the 16S rRNA gene and by qPCR. No impact of treatment was observed among vaccinated foals; however, marked and significant differences in microbial communities and diversity were observed between foals at 30 days of age relative to 2 days of age.ConclusionsThe results suggest age-related changes in the fecal microbial population of healthy foals do occur, however, mucosal vaccination does not result in major changes of the fecal microbiome in foals.

Development of the faecal microbiota in foals

“…Bordin et al [14] reported higher abundance of Firmicutes (65 vs. 40%) and lower abundance of Proteobacteria (15 vs. 37%) than the identified in our study, along with a much higher abundance of Verrucomicrobia (40 vs. 1%) in 30day-old foals. Bordin et al [14] reported higher abundance of Firmicutes (65 vs. 40%) and lower abundance of Proteobacteria (15 vs. 37%) than the identified in our study, along with a much higher abundance of Verrucomicrobia (40 vs. 1%) in 30day-old foals.…”

“…There are limited equine data to compare with these results. Bordin et al [14] reported higher abundance of Firmicutes (65 vs. 40%) and lower abundance of Proteobacteria (15 vs. 37%) than the identified in our study, along with a much higher abundance of Verrucomicrobia (40 vs. 1%) in 30day-old foals. That study also identified great variation of Verrucomicrobia among foals (0-48.7%), something that was not noted here.…”

“…Culture-independent methods have been used to monitor temporal changes in bacterial profiles from foals [12,13], but while such methods are suitable for the detection of population membership changes, they lack taxonomic classification to determine what the changes are. Recently, next generation sequencing has been used to provide detailed characterisation of the equine faecal microbiota, but study of foals has been limited to investigation of changes in the intestinal microbiota of foals at 2 timepoints [14].…”

Use of Serial Quantitative PCR of the vapA Gene of Rhodococcus equi in Feces for Early Detection of R. equi Pneumonia in Foals

“…Second, we were looking at relative rather than absolute differences between study groups, such that relative inhibition would have only been problematic if it were differentially distributed between cases and noncases. Last, we have used this extraction technique with success for extracting DNA both for microbiota studies and for fecal PCR 15, 27…”

Equine faecal microbiota transplant: Current knowledge, proposed guidelines and future directions

“…Foals pastured with their dams and other mares and foals were observed to ingest manure from their own dams and not from other mares or foals, immediately after defaecation, between the ages of 2-5 weeks and not before or after, suggesting an evolutionary adaptation for efficient inoculation of the GI tract (Francis-Smith and Wood-Gush 1977). Between Days 2 and 30 of age, increases in bacterial diversity and changes in relative abundance of the foals' faecal microbiota were noted (Bordin et al 2013). By Day 30, foals had developed a faecal microbiota that remained stable for the remainder of the first year of life (Faubladier et al 2014).…”