Pathology and Pathogenesis of Bacterial Infections

Abstract

Bacterial pathogens induce potent innate and adaptive immune responses, which, in the majority of situations, are able to eradicate an infection. Extracellular and intracellular bacterial pathogens induce different types of immune responses and have varying strategies for evading the host immune responses. This chapter on pathology and pathogenesis of bacterial infections summarizes the different types and mechanisms of pathology caused by bacteria once they cross mucosal or cutaneous barriers, and either multiply in extracellular spaces or take up residence within host cells. It illustrates how different types of immune responses can cause a variety of pathological damage to the host. The complement system is composed of over 20 different proteins and can be activated directly by extracellular bacteria in multiple ways. The interactions of chemokines and their receptors are critical for the recruitment of neutrophils and monocytes and the inflammatory response to infection. Mycobacterium tuberculosis is the most important chronic bacterial infection in humans, and is responsible for 9 million cases of TB and 1.9 million deaths annually. Extensive studies have identified the surface M protein as the major GAS protein, which stimulates cross-reactive T-cell response.