Factors influencing adherence of Streptococcus dysgalactiae to bovine mammary epithelial cell monolayers

Investigation of intramammary infections in primiparous cows during early lactation on organic dairy farms

Previous studies have shown that organically raised dairy cows have an increased prevalence of Staphylococcus aureus compared with conventionally raised dairy cows. However, little information exists about the dynamics of intramammary infection (IMI) in primiparous cows during early lactation on organic dairy farms. The objective of this study was to describe the IMI dynamics of primiparous cows on certified organic farms during early lactation. This longitudinal study enrolled 503 primiparous cows from 5 organic dairy farms from February 2019 to January 2020. Quarter-level milk samples were collected aseptically on a weekly basis during the first 5 wk of lactation. Samples were pooled by cow and time point into composite samples inside a sterilized laminar hood and submitted for microbiological culture. For each of the different microorganisms identified, we estimated the prevalence in each postpartum sample, period prevalence (PP), cumulative incidence, and persistence of IMI. Logistic regression models were used to investigate whether the prevalence of IMI differed by farm or sampling time points and whether IMI persistence differed between detected microorganisms. Our findings revealed a high prevalence of Staphylococcus aureus (PP = 18.9%), non-aureus staphylococci and closely related mammaliicoccal species (PP = 52.1%), and Streptococcus spp. and Streptococcus-like organisms (PP = 32.1%) within the study population. The prevalence of these microorganisms varied significantly between farms. Staphylococcus aureus and Staphylococcus chromogenes exhibited significantly higher IMI persistence compared with other detected bacterial taxa, confirming the divergent epidemiological behavior in terms of IMI chronicity across different microorganisms. This study improves our understanding of the epidemiology of mastitis-causing pathogens in organically raised primiparous cows, which can be used to tailor mastitis control plans for this unique yet growing subpopulation of dairy cows.

Use of the surface proteins GapC and Mig ofStreptococcus dysgalactiaeas potential protective antigens against bovine mastitis

Streptococcus dysgalactiae is a significant pathogen associated with bovine mastitis in lactating and nonlactating dairy cows, causing a severe inflammatory response of the mammary gland, which results in major economic losses to the dairy industry. Two proteins from S. dysgalactiae strain SDG8 were tested for their protective capacity against a homologous bacterial challenge in a dry cow model. The first was a bovine plasmin receptor protein (GapC), which shares 99.4% sequence identity to the plasmin-binding Plr protein of group A streptococci. The second protein product was Mig, a α2-M-, IgG-, and IgA-binding protein present on the cell surface of SDG8. We investigated the efficacy of immunization with purified recombinant forms of GapC and Mig by measuring the number of somatic cells and assessing the presence of the challenge strain in mammary secretions following challenge. In this model, we found that, although the number of quarters containing SDG8 was significantly reduced in the GapC- but not in the Mig-immunized animals, the somatic cell counts from teat secretions were significantly decreased in both the GapC and Mig vaccinates.Key words: Streptococcus dysgalactiae, bovine mastitis, Mig, GapC, GAPDH.

Studies about the mechanism of internalization by mammary epithelial cells of Escherichia coli isolated from persistent bovine mastitis

The purpose of this study was to investigate the interaction between Escherichia coli and primary mammary epithelial cell cultures derived from cows with persistent intramammary infection (IMI). Two strains of E. coli, isolated from the milk of two different cows suffering from persistent E. coli IMI were tested for adhesion to and invasion of three primary mammary epithelial cell cultures derived from mammary biopsies of the two infected cows. Intracellular E. coli were detected during five days post infection in vitro. Both strains of E. coli adhered to and invaded monolayers of all three primary mammary epithelial cell cultures. One strain adhered less but invaded more than the other. Comparison with other mammary pathogens indicated that E. coli invaded the cells less efficiently than Staphylococcus aureus, about as efficiently as Streptococcus dysgalactiae and more efficiently than Streptococcus uberis. The mechanism of E. coli invasion was studied using the cytoskeleton disrupting agents colchicine and cytochalasin D. These compounds inhibited the invasion of E. coli. Invasion of E. coli could also be inhibited by the phosphokinase inhibitors genistein and staurosporin in a dose-dependent fashion. Phorbol-myristyl-acetate (PMA) had no effect on the invasion of E. coli. Histology of mammary tissue revealed chronic inflammatory changes in quarters that were persistently infected by E. coli. Intracellular bacteria were not detected in mammary tissue sections. Polymerase chain reaction (PCR) analysis suggested that the two strains of E. coli lacked genes encoding for bundle-forming pili (bfpA), intimin (eae) and translocated intimin receptor (tir), which are characteristic for enteropathogenic E. coli (EPEC).

Characterization of mechanisms involved in uptake of Streptococcus dysgalactiae by bovine mammary epithelial cells

Bovine mammary epithelial cells were pretreated with inhibitors of protein kinase activity, actin polymerization and receptor-mediated endocytosis. In addition, mammary epithelial cells and Streptococcus dysgalactiae were pretreated with inhibitors of protein synthesis. Results showed that activity of tyrosine protein kinases, intact microfilaments and de novo eukaryotic protein synthesis was required for uptake of S. dysgalactiae by bovine mammary epithelial cells; a process that appeared to occur via receptor-mediated endocytosis. In contrast, de novo bacterial protein synthesis was not required for uptake of S. dysgalactiae by MAC-T cells. This study provides insight into bacterial and cellular mechanisms involved in early host-pathogen interactions, putting into perspective the role of mammary epithelial cells in the development and establishment of intramammary infections by S. dysgalactiae.