Abstract
S. bovis/S. equinus complex (SBSEC) includes lactic acid-producing bacteria considered as the causative agent associated with acute rumen lactic acidosis in intensive ruminants. Considering the limited information on the detailed characteristics and diversity of SBSEC in Korea and the emergence of antimicrobial resistance (AMR), we investigated the diversity of SBSEC from domestic ruminants and verified the presence of antimicrobial resistance genes (ARGs) against several antimicrobials with their phenotypic resistance. Among 51 SBSEC isolates collected, two SBSEC members (S. equinus and S. lutetiensis) were identified; sodA-based phylogenetic analyses and comparisons of overall genome relatedness revealed potential plasticity and diversity. The AMR rates of these SBSEC against erythromycin, clindamycin, and tetracycline were relatively lower than those of other SBSEC isolates of a clinical origin. An investigation of the ARGs against those antimicrobials indicated that tetracycline resistance of SBSECs generally correlated with the presence of tet(M)-possessing Tn916-like transposon. However, no correlation between the presence of ARGs and phenotypic resistance to erythromycin and clindamycin was observed. Although a limited number of animals and their SBSEC isolates were examined, this study provides insights into the potential intraspecies biodiversity of ruminant-origin SBSEC and the current status on antimicrobial resistance of the bacteria in the Korean livestock industry.
Highlights
The SBSEC has been recognized as commensal bacteria that inhabit the gastrointestinal tract of ruminants and humans, but numerous studies have provided evidence that the complex is an important contributor to ruminal acidosis in domestic ruminants and are associated with serious infections and colorectal cancer in humans and animals, highlighting the common importance of SBSEC members in the livestock industry and human health [15,16]
The exact economic damage caused by SBSEC in domestic animals is not currently clear, it is generally understood that the bacteria can affect animal health, productivity leading to important losses in the livestock industry [9]
SBSEC have been reported from various other domestic animals, their food products, and from companion wild animals only limited numbers of prevalence studies have been conducted on birds, cattle, and lambs [16]
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. The intensive management systems in the current livestock industry encourage the use of high-concentrate diets rather than high-forage diets in ruminants to enhance productivity and cost efficiency [1,2,3]. The rumen-bacterial community largely depends on the type of feed ingested by the host ruminants and rapid changes in the rumen bacterial community can significantly affect animal health and productivity [4,5]. Feeding ruminants with high-concentrate diets increases the level of non-fibrous carbohydrates, which promotes the proliferation of lactic acid producing amylolytic bacteria (e.g., Streptococcus bovis and Lactobacillus spp.) [6,7], with the accumulation of lactate leading to a rapid decrease in ruminal pH, causing acute rumen acidosis [8,9]. Rumen acidosis is reported to be associated with several clinical signs including intake depression, reduced fiber digestion, milk fat depression, diarrhea, ruminitis, lameness, liver abscesses, inflammation, pneumonia, and even death and it is considered one of the most important metabolic disorders in intensive ruminants [10]. 4.0/).
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