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Bovine mastitis, caused by Streptococcus agalactiae (Group B Streptococcus; GBS), poses significant economic challenges to the global dairy industry. Mouse models serves as valuable tools for assessing GBS-induced infections as an alternative to large animals. This study aimed to investigate the LD50 dose, organ bacterial load, and quantification of peritoneal leukocyte populations for GBS serotypes Ia and II isolates from China and Pakistan. Additionally, we measured indicators such as lactoferrin, albumin, and myeloperoxidase (MPO) activity. Pro-inflammatory cytokines (TNF-α, IL-1β, IL-6, and IL-2) and anti-inflammatory cytokines (IL-10 and TGF-β) in serum and tissue samples were evaluated using ELISA and qPCR, respectively. BALB/c mice (4 mice per group) received individual intraperitoneal injections of 100 μl containing specific bacterial inoculum concentrations (ranging from 105 to 109 CFU per mouse) of Chinese and Pakistani GBS isolates (serotypes Ia and II). Control groups received 100 μL of sterile PBS. Results revealed that the LD50 bacterial dose causing 50 % mortality in mice was 107 CFU. The highest bacterial load in all experimental groups was quantified in the peritoneum, followed by blood, mammary gland, liver, spleen, lungs, and brain. The most significant bacterial dissemination was observed in mice inoculated with Pakistani serotype Ia at 24 h, with a subsequent notable decline in bacterial counts at day 3. Notably, infection with Pakistani serotype Ia showed a trend of increased total leukocyte counts, significantly higher than Pakistani serotype II, Chinese Serotype Ia, and Chinese serotype II. A substantial influx of neutrophils and lymphocytes was observed in response to all tested serotypes, with Pakistani serotype Ia inducing a significantly higher influx compared to other groups (Pakistani serotype II, Chinese serotype Ia, and Chinese serotype II). Furthermore, TNF-α, IL-1β, IL-2, and IL-6 expressions were significantly increased in mice one day after infection with the Pakistani serotype Ia. Compared to mice infected with the Pakistani serotype II, Chinese Serotype Ia, and Chinese serotype II, those infected with the Pakistani serotype Ia isolate exhibited the highest production of IL-10 and TGF-β, along with significantly increased concentrations of lactoferrin, albumin, and MPO. These findings suggest that the persistence and severity of infection caused by the Pakistani serotype Ia may be linked to its ability to spread to deeper tissues. This study enhances our understanding of the clinical characteristics of bovine mastitis caused by S. agalactiae in China and Pakistan. • Pakistani GBS serotype Ia spreads faster than Pakistani serotype II, Chinese serotypes Ia/II in mice organs. • Pakistani serotype Ia induces higher pro/anti-inflammatory cytokines than serotype II, Chinese serotypes Ia/II in mice. • Pakistani serotype Ia raises more inflammatory indicators than serotype II, Chinese Ia/II in mice. • Mouse models offer practical GBS infection assessment as an alternative to large animals. [ABSTRACT FROM AUTHOR]

Lawsonia intracellularis is an obligate intracellular bacterium that cannot be cultured by conventional bacteriological methods. Pigs infected with L. intracellularis suffer from decreased daily weight gain and poor feed conversion ratio. China is a large producer of pigs, but epidemiological investigation data of L. intracellularis has not been obtained in recent years. Additionally, there is no information about a L. intracellulari s strain being successfully isolated and established in cell culture in China, and the above shortcomings limit understanding of the pathogenesis of L. intracellularis and alternative prevention and control methods. The aims of this study were to estimate the seroprevalence of L. intracellularis antibodies in eight major pig-producing provinces in China during 2019–2020, to isolate L. intracellularis from infected intestines and then to establish an infection model of L. intracellularis in mice. Our results showed that of the 3586 serum samples, 2837 (79.1%, 95% CI: 77.7%, 80.4%) were seropositive for the L. intracellularis antibody. Subsequently, the L. intracellularis strain LJS19051 from China was successfully isolated and established in cell culture. Furthermore, L. intracellularis DNA and antibodies could be detected in the feces and serum samples of infected mice, respectively. Moreover, infected crypts showed typical proliferative enteropathies (PE) lesions and L. intracellularis antigen was detected in infected mice by immunofluorescence at 28 days post inoculation. The results indicated that the new L. intracellularis strain LJS19051 was obtained and could successfully proliferate in ICR mice. • The seroprevalence of Lawsonia intracellularis antibodies in China during 2019–2020 were investigated. • L. intracellularis strain LJS19051 was isolated and established in cell culture. • The artificial infection model of LJS19051 in ICR mice was successfully established. [ABSTRACT FROM AUTHOR]