Dr. Ethel Bayer Santos is a FAPESP Young Investigator Fellow working at the Department of Microbiology at the University of Sao Paulo. She completed her PhD in 2013 under the supervision of Prof. Jose Franco da Silveira at the Federal University of Sao Paulo and Prof. Igor C. Almeida at the University of Texas at El Paso, studying the secretion pathways of the protozoan parasite Trypanosoma cruzi. She moved to Imperial College London to work as a postdoctoral fellow in the group of Prof. David W. Holden and identified the molecular mechanism of the Salmonella T3SS effector that suppresses T cell activation via MHCII downregulation. Ethel returned to Brazil and joined the group of Prof. Chuck Farah at the University of Sao Paulo where she characterized the function of the anti-amoeba Xanthomonas citri T6SS and the antibacterial Stenotrophomonas maltophilia T4SS. In 2018, Dr. Bayer Santos became a FAPESP Young Investigator and joined the Laboratory of Protein Structure and Evolution (LEEP), led by Prof. Cristiane Rodrigues Guzzo Carvalho and Prof. Robson Francisco de Souza, to start her own research group focused on the characterization of Salmonella spp. T6SS effectors.

Bacterial secretion systems are versatile structures that can secrete proteins into prokaryotic and eukaryotic cells. Many pathogenic bacteria rely on secretion systems to modulate host responses or to defend themselves against competing species and environmental predators. The type VI secretion system (T6SS) is a dynamic contractile weapon evolutionarily related to bacteriophage tails that delivers protein effectors into diverse cellular types, including rival bacteria and eukaryotic cells. This pool of secreted T6SS effectors represents a great reservoir of proteins with an unexpected broad range of biochemical activity. Antibacterial effectors are natural antimicrobials that bacteria have evolved over millions of years to effectively kill competitors, and effectors with anti-eukaryotic activities usually work against environmental amoeba predators and phagocytes of the immune system of vertebrate hosts, revealing conserved mechanisms of manipulation of cellular functions.

Salmonella species comprise a group of closely related organisms that exhibit different host specializations. Salmonella genus is divided into two species, S. bongori and S. enterica, with the later subdivided into ten subspecies and hundreds of serovars. These bacteria can be isolated from diverse environments and a wide range of hosts such as mammals, birds, reptiles, and plants. Human Salmonella infections are divided into diseases caused by typhoidal or non-typhoidal Salmonella (NTS). NTS disease is normally associated with zoonotic domesticated animals that are Salmonella reservoirs, with little or no sustained human-to-human transmission. However, invasive lineages of NTS have emerged in countries in sub-Saharan Africa, frequently associated with HIV infection. Salmonella species are high on the WHO priority list of pathogens that are critical for their growing antimicrobial resistance and Dr. Bayer-Santos´s group is using them as models to perform a systematic search and characterization of new T6SS effectors.