ABSTRACT
Microorganisms are incredibly diverse, and include bacteria, archaea, fungi, protozoa, and viruses. They all abound in our environment and, when grown in ideal conditions, have an impact on our lives. All living entities less than 1 mm in diameter fall into the world of microbes. Among microorganisms, bacteria are found to be the most prevalent in nature, accounting for around 90–95% of the microorganisms. A host’s vulnerability to infection caused by bacteria or their by-products is referred to as microbial pathogenesis. This occurs once the host and pathogen acquire a sophisticated form of interaction. During the history of evolution, a large number of pathogenic bacteria that cause disease have evolved a variety of virulence processes and genes or factors able to encode for pathogenicity that create proteins or other biomolecules in an inducible or constitutive manner. Along with other intrinsic mechanisms, such as the number of microbial entities supplied in the host system, the route of administration, and a host specific defensive mechanism, the many virulence factors involved are often what define the degree of disease. This chapter gives a conceptual overview of numerous microorganisms, their pathogenesis, and the immune system’s reaction to the pathogens.
