ABSTRACT
BACKGROUND: There is renewed interest towards understanding the host-pathogen interaction in the light of epigenetic modifications. Although epithelial tissue is the major site for host-pathogen interactions, there is handful of studies to show how epithelial cells respond to pathogens. Bacterial infection in the mammary gland parenchyma induces local and subsequently systemic inflammation that results in a complex disease called mastitis. Globally Staphylococcus aureus is the single largest mastitis pathogen and the infection can ultimately result in either subclinical or chronic and sometimes lifelong infection. RESULTS: In the present report we have addressed the differential inflammatory response in mice mammary tissue during intramammary infection and the altered epigenetic context induced by two closely related strains of S. aureus, isolated from field samples. Immunohistochemical and immunoblotting analysis showed strain specific hyperacetylation at histone H3K9 and H3K14 residues. Global gene expression analysis in S. aureus infected mice mammary tissue revealed a selective set of upregulated genes that significantly correlated with the promoter specific, histone H3K14 acetylation. Furthermore, we have identified several differentially expressed known miRNAs and 3 novel miRNAs in S. aureus infected mice mammary tissue by small RNA sequencing. By employing these gene expression data, an attempt has been made to delineate the gene regulatory networks in the strain specific inflammatory response. Apparently, one of the isolates of S. aureus activated the NF-κB signaling leading to drastic inflammatory response and induction of immune surveillance, which could possibly lead to rapid clearance of the pathogen. The other strain repressed most of the inflammatory response, which might help in its sustenance in the host tissue. CONCLUSION: Taken together, our studies shed substantial lights to understand the mechanisms of strain specific differential inflammatory response to S. aureus infection during mastitis. In a broader perspective this study also paves the way to understand how certain bacteria can evade the immune surveillance and cause sustained infection while others are rapidly cleared from the host body.
ABSTRACT
Streptococci are one among the major mastitis pathogens which have a considerable impact on cow health, milk quality, and productivity. The aim of the present study was to investigate the occurrence and virulence characteristics of streptococci from bovine milk and to assess the molecular epidemiology and population structure of the Indian isolates using multilocus sequence typing (MLST) and pulsed-field gel electrophoresis (PFGE). Out of a total of 209 bovine composite milk samples screened from four herds (A-D), 30 Streptococcus spp. were isolated from 29 milk samples. Among the 30 isolates, species-specific PCR and partial 16S rRNA gene sequence analysis identified 17 Streptococcus agalactiae arising from herd A and 13 Streptococcus uberis comprising of 5, 7, and 1 isolates from herds B, C, and D respectively. PCR based screening for virulence genes revealed the presence of the cfb and the pavA genes in 17 and 1 S. agalactiae isolates, respectively. Similarly, in S. uberis isolates, cfu gene was present in six isolates from herd C, the pau A/skc gene in all the isolates from herds B, C, and D, whereas the sua gene was present in four isolates from herd B and the only isolate from herd D. On MLST analysis, all the S. agalactiae isolates were found to be of a novel sequence type (ST), ST-483, reported for the first time and is a single locus variant of the predicted subgroup founder ST-310, while the S. uberis isolates were found to be of three novel sequence types, namely ST-439, ST-474, and ST-475, all reported for the first time. ST-474 was a double locus variant of three different STs of global clonal complex ST-143 considered to be associated with clinical and subclinical mastitis, but ST-439 and ST-475 were singletons. Unique sequence types identified for both S. agalactiae and S. uberis were found to be herd specific. On PFGE analysis, identical or closely related restriction patterns for S. agalactiae ST-483 and S. uberis ST-439 in herds A and B respectively, but an unrelated restriction pattern for S. uberis ST-474 and ST-475 isolates from herds D and C respectively, were obtained. This signifies that the isolates of particular ST may exhibit related PFGE patterns suggesting detection of a faster molecular clock by PFGE than MLST. Since all the isolates of both the species belonged to novel sequence types, their epidemiological significance in global context could not be ascertained, however, evidence suggests that they have uniquely evolved in Indian conditions. Further research would be useful for understanding the role of these pathogens in bovine sub-clinical mastitis and implementing effective control strategies in India.
