Use of molecular epidemiology of bovine Staphylococcus aureus and Streptococcus agalactiae to guide vaccine development and improved control measures for contagious mastitis in Brazil
Project summary
Brazil is one of the largest milk producers worldwide, but its dairy industry has suffered great economic losses due to contagious bovine mastitis (CBM), an infectious disease caused mainly by the bacterial species Streptococcus agalactiae (GBS) and Staphylococcus aureus (SAU). CBM control in Brazil is difficult because most dairy farms run small family farms with limited professional training. Farmers often use antibiotics for treatment and prevention of mastitis without proper guidance. This practice contributes to the risk of antimicrobial resistance in the bacteria, which can infect people as well as cows. Not all GBS and SAU are equal. There is variability in certain bacterial structures, including those that are present on their outer surface (e.g. carbohydrates and proteins). These polymorphic cell surface structures allow the classification of SAU and GBS strains into different types. Knowledge of the distribution of those types is essential for development of disease control tools, such vaccines and management strategies. Currently, there is a lack of knowledge on CBM-causing SAU and GBS in Brazil, partly because current diagnostic and typing methods are expensive and usually restricted to research laboratories. There is an urgent need for the development of faster and cheaper methods, improved surveillance, better CBM control measures and vaccine development studies. We aim to collect unprecedented information on SAU and GBS types on Brazilian dairy farms, to evaluate new diagnostic and typing methods, and to inform future studies for vaccine design. Our analysis of SAU and GBS strains from Southeastern and Northern Brazil will provide better understanding of their potential to cause CBM, and it will guide mastitis control policies, public health recommendations, including the rational use of antimicrobials, and inform vaccine design. Moreover, our international scientific collaboration will foster the scientific and professional development of a promising young LMIC-based female scientist.
Project outcomes
Brazil is a top-5 milk producer globally, but its dairy industry suffers major losses from contagious bovine mastitis (CBM) caused by Staphylococcus aureus (SAU) and Streptococcus agalactiae (GBS). CBM control is challenging because 70% of dairies are small family farms and use antibiotics without proper advice. SAU and GBS are highly heterogeneous pathogens. Surveillance of their molecular and cellular characteristics (e.g., capsule, surface proteins) is a crucial step towards design of vaccines to prevent CBM. We lack data on strain-specific characteristics of SAU and GBS in Brazilian herds because genomic methods are expensive and restricted to research-specialized laboratories. In this project, we intend to develop a locally appropriate alternative method based on MALDI-TOF MS for molecular typing of GBS and SAU to enhance our knowledge of molecular epidemiology, inform vaccine development, and aid in antimicrobial stewardship efforts. In Brazil, MALDI-TOF MS stands out as alternative approach for simultaneous diagnosis and strain-typing as this technology is fast, cheap, and available in most third-party laboratories. We also gathered unprecedented genomic data on SAU and GBS (historical and current) from bovine milk in Brazil. Isolates represented major dairy regions in the country, which have different farm types. We showed the usefulness of MALDI-TOF MS for species identification (in milk and on pure cultures), and to identify biomarkers for strain-typing (constitutively and universally expressed vs strain-specific proteins). We also demonstrated the potential of CRISPR1-RFLP for molecular typing and differentiation of GBS clones from bovine and human hosts. Data derived from whole genome sequences show the circulation of multi-host (CC103/serotype Ia) and bovine adapted GBS lineages (CC91/serotype III) in dairy farms, and strain replacement possibly driven by the acquisition of antimicrobial resistance (AMR) genes. Most GBS and SAU strains harboured AMR markers (genes and mobile genetic elements) that confer resistance to antimicrobial agents commonly used for treatment (human and veterinary medicine settings) and growth promotion (beta-lactams, macrolides, lincosamides, aminoglycosides, tetracycline) in Brazil, highlighting the circulation of methicillin resistant SAU (MRSA) and clindamycin-resistant GBS strains which are recognized as global public health threats. Importantly, however, most GBS was susceptible to penicillin whereas most SAU was not. This implies that narrow spectrum antimicrobials can be used for treatment of GBS to reduce the risk of selection for AMR, whilst also highlighting the need for easy and affordable access to diagnostics that can differentiate between GBS and SAU. Furthermore, we expanded the project to included additional isolate collections, including piscine GBS isolates. CC552 represented the predominant clone among fish isolates, but 33% of them belonged so ST283, a hypervirulent lineage associated with foodborne outbreak of invasive disease in humans, indicating significant zoonotic potential. Data generated in this study can be used to guide local farmers and policymakers on CBM control practices, including antibiotic choice and vaccine targets for future investigation. In addition, our results shed light on the epidemiologic scenario of piscine GBS in Brazil, where it has emerged as an important and potentially zoonotic pathogen in aquaculture. This fellowship fostered professional development, strengthened the international network, improved research skills of a promising young middle-income country-based female scientist, and established new national and international collaborations that will continue beyond the current project.
