Proteomic Characterization of Antibiotic Resistance, and Production of Antimicrobial and Virulence Factors in Streptococcus Species Associated with Bovine Mastitis

4th International Caparica Conference in Antibiotic Resistance, Caparica, Portugal, 13th – 17th June 2021Streptococcus spp. are among the main mastitis pathogens present in dairy products [1]. The major species involved in both clinical and subclinical mastitis are Streptococcus agalactiae, Streptococcus canis, Streptococcus dysgalactiae and Streptococcus uberis, which produce a variety of virulence factors that are involved in streptococcal pathogenicity. These include neuraminidase, pyrogenic exotoxin, and M protein, and in addition they might produce bacteriocins and antibiotic-resistance proteins [2]. Unjustifiable misuse of antimicrobials has led to an increase in antibiotic-resistant bacteria present in foodstuffs [3]. Identification of the mastitis-causing bacterial strain, as well as determining its antibiotic resistance and sensitivity is crucial for effective therapy. Classic culture-based methods used for the detection of pathogenic bacteria are time-consuming and laborious procedures. The present work focused on the LC–ESI–MS/MS (liquid chromatography–electrospray ionization tandem mass spectrometry) analysis of tryptic digestion peptides from mastitis-causing Streptococcus spp. isolated from milk. A total of 100 μg of protein extraction was digested with trypsin, cleaned on a C18 microSpinTM, and analyzed by LC-MS/MS. Proteomic data were processed by SEQUEST (Proteome Discoverer 1.4 package, Thermo Fisher Scientific) against bacteria in the UniProt/TrEMBL database. A total of 2706 non-redundant peptides belonging to 2510 proteins was identified and analyzed. Among them, 168 peptides were determined, representing proteins that act as virulence factors, toxins, anti-toxins, provide resistance to antibiotics that are associated with the production of lantibiotic-related compounds, or play a role in the resistance to toxic substances. Protein comparisons with the NCBI database allowed the identification of 134 peptides as specific to Streptococcus spp., while two peptides (EATGNQNISPNLTISNAQLNLEDKNK and DLWC*NM*IIAAK) were found to be species-specific to Streptococcus dysgalactiae. This proteomic repository might be useful for further studies and research work, as well as for the development of new therapeutics for the mastitis-causing Streptococcus strainsN