Microbial pathogens include bacteria, viruses, fungi, and parasites and together account for a significant percentage of acute and chronic human diseases. In addition to understanding the mechanisms by which various pathogens cause human disease, research in microbial pathogenesis also addresses mechanisms of antimicrobial resistance and the development of new antimicrobial agents and vaccines. Answering fundamental questions regarding host-microbe interactions requires an interdisciplinary approach, including microbiology, genomics, informatics, molecular and cellular biology, biochemistry, immunology, and epidemiology. erplay between host and microbe. Studies investigated the direct effects of pollutants on respiratory tract infections are very vast, but those interested in the role of a pre-existing disease and effects of the exposure on the response to secondary stresses are few. In an experimental study at concentrations of air pollutants found in urban environments, frank toxicological responses are rarely observed; however, exposure to a secondary stress like respiratory challenge with infectious bacteria can exacerbate the response of the experimental host. Environmental pollution is defined as the undesirable change in physical, chemical and biological characteristics of our air, land and water. According to the essential concepts of ecology, any form of life could be called as " an ecosystem " provided that the two domains of factors are present: the first part named as the " biotic factors " , this include: producers,
