Bacterial infectious diseases are diseases that can be caused by the invasion and multiplication of bacteria in a host organism if the pathogen has special disease-causing properties (pathogenicity) or the host's defense mechanisms are impaired. The interaction between the bacterium and the host organism determines the occurrence and severity of an infectious disease. As diverse as the group of bacterial pathogens is, as numerous and different are the diseases caused in animals and humans. Only a very small proportion of all known bacterial species are pathogenic to animals or humans. The majority of bacteria found in the environment are apathogenic. Bacterial infectious diseases are the most common cause of death worldwide. Since the bacteriological discoveries of the 19. Since bacteria cause a variety of diseases in humans and animals in the early twentieth century, the prevention of bacterial infections by hygiene and their treatment by antibiosis is a central problem of medicine. Until the development of specific antibacterial therapies and hygiene measures, the "classic" bacterial epidemics such as plague, diphtheria, cholera or typhus were feared as deadly epidemics. At present, bacterial diarrheal diseases are a common occurrence in countries with poor hygienic conditions. Nosocomial infections with highly resistant bacteria in the foreground in industrialized countries.
Bacterial infectious diseases of plants are very different from those of animals with respect to the spectrum of pathogens, infection strategies, dissemination, and defense mechanisms (see on plant disease). The same applies to specific bacterial infections in arthropods, such as insects. The concept of infection is related to the invasion of. Limiting the multiplication of the pathogen. Damage to the host by the pathogen. The subsequent defense reactions of the host in case of infection defined. A pathological, self-damaging defense reactions of the host according to of a bacterial infection, that is, after the elimination of the pathogen, is not addressed as a bacterial infectious disease, although the cause is the original infection. These secondary diseases are called post- or parainfectious syndromes. If the bacterium multiplies but does not penetrate the ties, as is the case with most bacteria on the skin or in the oral cavity, for example, it is referred to as bacterial colonization. This also applies to bacteria that occur as commensals or symbionts in the gastrointestinal tract as so-called intestinal flora, as the gastrointestinal tract is anatomically considered to be "outside". If harmful bacterial metabolites (exotoxins) enter the host during such colonization, this is a bacterial intoxication.
Colloquially, acute bacterial infectious diseases of the respiratory tract are also abbreviated as bacterial infections the term.
Interaction between host and bacterial pathogen
An infectious disease results from the disease-causing properties of a pathogen and the host's responses to the pathogen's invasion and replication. However, a pathogen does not cause a disease in every case; rather, the course and symptoms of a bacterial infectious disease are the result of a very complex and dynamic interaction between host and pathogen. In the course of millions of years of co-evolution of both, host organisms developed increasingly specific defense mechanisms, starting with simple phagocytosis of the pathogen (uptake into the cell and destruction by intracellular digestion), mechanical and enzymatic barriers, development of a non-specific defense system with the help of plasma proteins (complement system), to the specific cellular system of T-lymphocytes and non-cellular (humoral), specific antibodies. For their part, bacterial pathogens continued to develop new molecular and biochemical mechanisms to subvert these individual defense barriers. Due to the very short generation time of bacteria compared to host organisms (20 minutes to a few hours compared to several years), bacterial pathogens can produce variants much faster and react to new defense mechanisms. These evolutionary mechanisms play a role not only in phylogenetic evolution, but also in the individual host organism in the course of an infection. Such rapid microevolution of the bacterial population is also a reason for the emergence of resistance to antibacterial therapies.