Biology subjects

Holman, D. B.

Publications and source records attributed to Holman, D. B..

4 recordsLinked to original sources

bioRxiv2021

Characterization of the microbiota associated with 12-week-old bovine fetuses exposed to divergent in utero nutrition

A recent study reported the existence of a diverse microbiota in 5-to-7-month-old calf fetuses, suggesting that colonization of the bovine gut with so-called "pioneer" microbiota may begin during mid-gestation. In the present study, we investigated 1) the presence of microbiota in bovine fetuses at early gestation (12 weeks), and 2) whether the fetal microbiota is influenced by the maternal rate of gain or dietary supplementation with vitamins and minerals (VTM) during early gestation. Amniotic and allantoic fluids, and intestinal and placental (cotyledon) tissue samples obtained from fetuses (n = 33) on day 83 of gestation were processed for the assessment of fetal microbiota using 16S rRNA gene sequencing. The sequencing results revealed that a diverse and complex microbial community was present in each of these fetal compartments evaluated. Allantoic and amniotic fluids, and fetal intestinal and placenta microbiota each had distinctly different (0.047 [≥] R2 [≥] 0.019, P [≤] 0.031) microbial community structures. Allantoic fluid had a greater (P < 0.05) microbial richness (number of OTUs) (Mean 122) compared to amniotic fluid (84), intestine (63) and placenta (66). Microbial diversity (Shannon index) was similar for the intestinal and placental samples, and both were less diverse compared with fetal fluid microbiota (P < 0.05). Thirty-nine different archaeal and bacterial phyla were detected across all fetal samples, with Proteobacteria (55%), Firmicutes (16.2%), Acidobacteriota (13.6%) and Bacteroidota (5%) predominating. Among the 20 most relatively abundant bacterial genera, Acidovorax, Acinetobacter, Brucella, Corynebacterium, Enterococcus, Exiguobacterium and Stenotrophomonas differed by fetal sample type (P < 0.05). A total of 55 taxa were shared among the four different microbial communities. qPCR of bacteria in the intestine and placenta samples as well as scanning electron microscopy imaging of fetal fluids provided additional evidence for the presence of a microbiota in these samples. Minor effects of maternal rate of gain and VTM supplementation, and their interactions on microbial richness and composition were detected. Overall, the results of this study indicate that colonization with pioneer microbiota may occur during early gestation in bovine fetuses, and that that the maternal nutritional regime during gestation may influence the early fetal microbiota.

microbiology↗

bioRxiv2021

The nasopharyngeal, ruminal, and vaginal microbiota and the core taxa shared across these microbiomes in virgin yearling heifers exposed to divergent in utero nutrition during their first trimester of gestation and in pregnant beef heifers in response to mineral supplementation

Emerging evidence has indicated that microbial transmission from the bovine dam to her fetus may take place before birth, and that the maternal microbiota during pregnancy modulates programming of fetal metabolic and nervous system development, highlighting the potential and extended role of the maternal microbiome in calf health and development. In the present study, we characterized the nasopharyngeal, ruminal and vaginal microbiota from two cohorts of beef heifers managed at the same location: 1) virgin yearling heifers (9 months old) born from dams received gestational diets which resulted in low (LG, n = 22) or medium (MG, n = 23) weight gain during the first 84 days of gestation; and 2) pregnant replacement heifers that received a vitamin and mineral supplement (VTM, n = 17) or not (Control, n = 15) during the first 6 months of gestation. Nasopharyngeal and vaginal swabs as well as ruminal fluid were collected from both cohorts and the microbiota of each sample was assessed using 16S rRNA gene sequencing. In addition to the comparison between treatment groups within each cohort, the similarity of the microbiota of the three sample types were evaluated, and shared taxa amongst these communities were identified. The bacterial genera present in the rumen and vagina that can influence methanogenic archaeal genera were predicted using a stepwise-selected generalized linear mixed model. No significant difference was observed in the alpha and beta diversity in any of the nasopharyngeal, ruminal and vaginal microbiota between LG and MG offspring virgin heifers, or between the control and VTM pregnant heifers (p > 0.05). Subtle compositional changes in the vaginal microbiota in yearling heifers, and in the nasopharyngeal and ruminal microbiota of pregnant heifers were detected in response to treatments. Forty-one archaeal and bacterial OTUs were shared by over 60% of all samples from both virgin and pregnant heifers. Two taxa within the Methanobrevibacter genus were identified as core taxa and this genus was more relatively abundant in pregnant heifers compared to virgin heifers. Among the 25 top genera, Prevotella and Prevotella UCG-003 (negative) and Christensenellaceae R-7 group (positive) were predicted to have a significant effect on ruminal Methanobrevibacter spp. The results of this study indicate that there is little impact of divergent gestational nutrition during the first trimester on the calf microbiome at 9 months postnatal, and that VTM supplementation during pregnancy may not alter the maternal microbiome. This study provides evidence that there are several microbial taxa, including methanogenic archaea, that are shared across the respiratory, gastrointestinal, and reproductive tracts, suggesting the need for a holistic evaluation of the bovine microbiota when considering potential maternal sources for seeding calves with pioneer microbiota.

microbiology↗

bioRxiv2021

A Longitudinal Study of Antimicrobial Resistance in Enterococcus spp. Isolated from a Beef Processing Plant and Retail Ground Beef

Antimicrobial use in food-producing animals has come under increasing scrutiny due to its potential association with antimicrobial resistance (AMR). Monitoring of AMR in indicator microorganisms such as Enterococcus spp. in meat production facilities and retail meat products can provide important information on the dynamics and prevalence of AMR in these environments. In this study, swabs or samples were obtained from various locations in a commercial beef packing operation (n = 600 total) and from retail ground beef (n = 60) over a 19-month period. All samples/swabs were enriched for Enterococcus spp. and suspected enterococci isolates were identified using species-specific PCR primers. Enterococcus faecalis was the most frequently isolated species followed by Enterococcus hirae, which was found mostly on hides and ground beef. Enterococcus faecium (n = 9) and E. faecalis (n = 120) isolates were further characterized for antimicrobial resistance and resistant genes due to the clinical significance of these species. Twenty-one unique AMR profiles were identified, with 90% of isolates resistant to at least two antimicrobials, and two that were resistant to nine antimicrobials. Tetracycline resistance was observed most often in E. faecalis (28.8%) and was likely mediated by tet(M). Genomic analysis of selected E. faecalis and E. faecium isolates revealed that many of the isolates in this study clustered with other publicly available genomes from ground beef, suggesting that these strains are well adapted to the beef packaging environment. IMPORTANCEAntimicrobial resistance (AMR) is a serious challenge facing the agricultural industry. Understanding the flow of antimicrobial resistant-bacteria through the beef fabrication process and into ground beef is an important step in identifying intervention points for reducing AMR. In this study we used enterococci as indicator bacteria for monitoring AMR in a commercial beef packaging facility and in retail ground beef over a 19-month period. Although washing of carcasses post-hide removal reduced the isolation frequency of Enterococcus spp., a number of antimicrobial resistant-Enterococcus faecalis isolates were recovered from ground beef produced in the packaging plant. Genome analysis showed that several E. faecalis isolates were genetically similar to publicly available isolates recovered from retail ground beef in the United States.

microbiology↗

bioRxiv2021

Weaning age and its effect on the development of the swine gut microbiome and resistome

Piglets are often weaned between 19 and 22 d of age in North America although in some swine operations this may occur at 14 d or less. Piglets are abruptly separated from their sow at weaning and are quickly transitioned from sows milk to a plant-based diet. The effect of weaning age on the long-term development of the pig gut microbiome is largely unknown. Here, pigs were weaned at either 14, 21, or 28 d of age and fecal samples collected 20 times from d 4 (neonatal) through to marketing at d 140. The fecal microbiome was characterized using 16S rRNA gene and shotgun metagenomic sequencing. The fecal microbiome of all piglets shifted significantly three to seven days post-weaning with an increase in microbial diversity. Several Prevotella spp. increased in relative abundance immediately after weaning as did butyrate-producing species such as Butyricicoccus porcorum, Faecalibacterium prausnitzii, and Megasphaera elsdenii. Within 7 days of weaning, the gut microbiome of pigs weaned at 21 and 28 days of age resembled that of pigs weaned at 14 d. Resistance genes to most antimicrobial classes decreased in relative abundance post-weaning with the exception of those conferring resistance to tetracyclines and macrolides-lincosamides-streptogramin B. The relative abundance of microbial carbohydrate-active enzymes (CAZymes) changed significantly in the post-weaning period with an enrichment of CAZymes involved in degradation of plant-derived polysaccharides. These results demonstrate that the pig gut microbiome tends change in a predictable manner post-weaning and that weaning age has only a temporary effect on this microbiome. ImportancePiglets are abruptly separated from their sow at weaning and are quickly transitioned from sows milk to a plant-based diet. This is the most important period in commercial swine production yet the effect of weaning age on the long-term development of the pig gut microbiome is largely unknown. Metagenomic sequencing allows for a higher resolution assessment of the pig gut microbiome and enables characterization of the resistome. Here we used metagenomic sequencing to identify bacterial species that were enriched post-weaning and therefore may provide targets for future manipulation studies. In addition, functional profiling of the microbiome indicated that many carbohydrate and metabolic enzymes decrease in relative abundance of after weaning. This study also highlights the challenges faced in reducing antimicrobial resistance in pigs as genes conferring tetracycline and macrolide resistance remained relatively stable from 7 days of age through to market weight at 140 d despite no exposure to antimicrobials.

microbiology↗