Molecular epidemiology, characterization of virulence factors and antibiotic resistance profile of Streptococcus agalactiae isolated from dairy farms in China and Pakistan

Streptococcus agalactiae is one of the most common pathogens that cause bovine mastitis worldwide. Identifying pathogen prevalence and virulence factors is critical for developing prevention and control approaches. Herein, 1 161 milk samples from various dairy farms in China(n=558) and Pakistan(n=603) were collected between 2019–2021 and were subjected to S. agalactiae isolation. Prevalence, serotyping, virulence genes, and antibiotic-resistant genes of S. agalactiae were evaluated by PCR assay. All isolates were characterized for haemolysis, biofilm production, cytotoxicity, adhesion, and invasion on bovine mammary epithelial cells. The prevalence of S. agalactiae-induced mastitis in cattle was found to be considerably higher in Pakistan than in China. Jiangsu and Sindh provinces had the highest area-wise prevalence in China and Pakistan, respectively. Serotypes Ia and II were prevalent in both countries, whereas serotype III was found only in Pakistan. Moreover, all isolates tested positive for PI-2b gene but negative for PI-1 and PI-2a genes. All isolates harboured cfb, cylE, hylB, and fbsB virulent genes, whereas many of them lacked bibA, rib and bca. However, the absence of bac and scp genes in Chinese isolates and cspA in Pakistani isolates was noted, while spb1 and lmb were not detected in isolates of both countries. Pakistani isolates, particularly serotype Iapositive, had a considerably higher ability to produce biofilm, haemolysis, cytotoxicity, adhesion, and invasion than Chinese isolates. Most of the isolates were phenotypically resistant to tetracycline, erythromycin, and clindamycin and genotypic resistance was confirmed by the presence of ermA, ermB, tetM and tetO genes. Our study highlights the antimicrobial resistance profile and virulence-related factors contributing to the epidemiological spread of mastitis-causing S. agalactiae in China and Pakistan. The findings may facilitate future studies designed to develop improved treatment and control strategies against this pathogen.

Toxicological effects of nanoselenium in animals

The productivity and sustainability of livestock production systems are heavily influenced by animal nutrition.To maintain homeostatic balance in the body of the animal at different phases of life,the percentage of organically active minerals in livestock feed must be optimized.Selenium(Se)is a crucial trace mineral that is required for the maintenance of many functions of the body.Se nanoparticles(SeNPs)attracted considerable interest from researchers for a variety of applications a decade ago,owing to their extraordinary properties.SeNPs offer significant advantages over larger-sized materials,by having a comparatively wider surface area,increased surface energy,and high volume.Despite its benefits,SeNP also has toxic effects,therefore safety concerns must be taken for a successful application.The toxicological effects of SeNPs in animals are characterized by weight loss,and increased mortality rate.A safe-by-strategy to certify animal,human and environmental safety will contribute to an early diagnosis of all risks associated with SeNPs.This review is aimed at describing the beneficial uses and potential toxicity of SeNPs in various animals.It will also serve as a summary of different levels of SeNPs which should be added in the feed of animals for better performance.