Bovine vegetative endocarditis caused by Streptococcus suis

Development and Evaluation of Non-Antibiotic Growth Promoters for Food Animals

The widespread utilization of antibiotic growth promoters (AGPs) boosts the growth rate of food animals and enhances human living standards. Nevertheless, it is accompanied by escalating antibiotic resistance. Consequently, there is an urgent demand to develop novel alternatives to growth promoters. The objective of this study was to develop a non-antibiotic growth promoter (NAGP) for augmenting the growth rate of food animals. The growth-promoting effect of plant-derived NAGPs was assessed in mice and broiler chickens, and its growth-promoting mechanism was initially investigated. The results reveal that a combination of hawthorn (also known as shanzha) and astragalus (also known as huangqi) extracts (SQ) enhanced the growth rate of mice both in vivo and in vitro, attributed to their significant capacity to promote muscle growth and improve immunity (p < 0.05). The composite super energy extract M (CSEE-M), further optimized on the basis of SQ, significantly improved growth performance and feed conversion ratio, and elevated the activity of intestinal digestive enzymes (p < 0.05) in both mice and broilers and reshaped the gut microbiota of broilers. The addition of 0.5% CSEE-M to broiler drinking water significantly increased muscle content and improved carcass quality (p < 0.05). In conclusion, both SQ and CSEE-M hold great promise as NAGPs and serve as effective substitutes to AGPs. This research not only furnishes new solutions for the misuse of antibiotics but presents a fresh perspective for the development of growth promoters.

Genotypic diversity of Streptococcus suis and the S. suis-like bacterium Streptococcus ruminantium in ruminants

Although Streptococcus suis has attracted public attention as a major swine and human pathogen, this bacterium has also been isolated from other animals, including ruminants. However, recent taxonomic studies revealed the existence of other species that were previously identified as S. suis, and some of these isolates were reclassified as the novel species Streptococcus ruminantium. In Japan, biochemically identified S. suis is frequently isolated from diseased ruminants; however, such isolates have not yet been identified accurately, and their aetiological importance in ruminants is unclear. Therefore, to understand the importance of S. suis and S. suis-like bacteria in ruminants, we reclassified S. suis isolates from ruminants according to the updated classification and investigated their genetic diversity. Although both S. suis and S. ruminantium were isolated from healthy and diseased ruminants, most of the isolates from diseased animals were S. ruminantium, implying that S. ruminantium is more likely to be associated with ruminant disease than S. suis. However, the ruminant S. suis and S. ruminantium isolates from diseased animals were classified into diverse genotypes rather than belonging to certain clonal groups. Genome sequence analysis of 20 S. ruminantium isolates provided information about the antibiotic resistance, potential virulence, and serological diversity of this species. We further developed an S. ruminantium-specific PCR assay to aid in the identification of this bacterium. The information obtained and the method established in this study will contribute to the accurate diagnosis of ruminant streptococcal infections.