Neutrophils, as the main cells of the first line of host defense against microbial pathogens, are responsible for pathogen recognition, inhibition of pathogen spreading into the host tissue, and finally, killing the invader cells. Neutrophils carry out these functions via numerous mechanisms, including a relatively recently described activity based on a release of neutrophil extracellular traps (NETs), a process called netosis. NETs are structures composed of DNA backbone, decorated with antimicrobial factors, derived from neutrophil granules. The structure of NETs and their enzymatic and microbicidal inclusions enable efficient trapping and killing of microorganisms within the neutrophil extracellular space. However, the efficiency of NETs depends on neutrophil ability to recognize pathogen signals and to trigger rapid responses. In this chapter, we focus on possible pathways involved in the release of NETs and summarize the current knowledge on triggers of this process during bacterial, fungal, protozoan, and viral infections. We also consider the mechanisms used by microorganisms to evade NET-killing activity and analyze the harmful potential of NETs against the host cells and the contribution of NETs to noninfectious human diseases.
Part of the book: Role of Neutrophils in Disease Pathogenesis
Biofilm is a compact coating formed on various artificial and physiologic surfaces by a population of microorganisms which in this habitat establish a close cooperation, exploiting both the physical interactions that stabilize the community and chemical cooperation, engaging numerous agents to modify the environment, i.e., to influence the acidity, nutrient acquisition, or oxygen availability. Microorganisms can also communicate using quorum-sensing molecules carrying specific messages. Some microbes temporarily dominate, while others are constantly replaced by different community members. But these co-operations or competitions have a deep sense—they serve to protect the whole community against the defense system of the host to assure survival. The oral cavity is inhabited by diverse microorganisms, including bacteria, but also yeast-like fungi from the genus Candida that stay under a tight control of the host as long as its immune system is not weakened; then these relatively mild commensals convert to dangerous pathogens that start the invasion often in collaboration with other microbes. Elongated hyphal forms of fungal cells favor the biofilm type of growth and communication with other microbes supporting immune resistance of the biofilm. In this chapter, we discuss the mechanisms of interactions between bacteria and C. albicans in the oral cavity, their communication, host responses, and possible strategies of anti-biofilm treatment.
Part of the book: Candida Albicans