**2. Immune view**

A good immune system is essential for the survival of any organism because of the protection against infectious beings. It is the principal infections evolution blocker that may cause elevated decease rate. This is a well-established fact for almost all known infective illness; the number of subjects in contact with the infectious agents is greater than those who really evolve diseases.

Contaminations occurred by no cell invasive bacteria are the most common. In these cases, the immune system of shield is mostly associated to the harborer's innate barriers, natural protection mechanisms, and antibody production. The importance of innate barriers (**Table 1**) in the combat against no cell invasive bacterial infections is well-known [21]. The integrity of skin and mucosa prevent adherence and penetration of bacteria; mucociliary movement eliminates bacteria from the respiratory tract; the stomach's acidic pH destroys some bacteria penetrating by the upper digestive tract; and in the saliva, eyes secretion, and prostatic secretion, lysozyme and other substances have antimicrobial activity.


**Table 1.** Barriers against infectious microorganisms.

Europe, most precisely in Germany. The implicated agent was an enterohemorrhagic *E. coli* (EHEC), which presented virulence traits of both, a verotoxigenic *E. coli* (VTEC) and enteroag-

102 *Escherichia coli* Escherichia coli - Recent Advances on Physiology, Pathogenesis and Biotechnological Applications - Recent Advances on Physiology, Pathogenesis and Biotechnological Applications

A relevant study involving enterotoxigenic *E. coli* STb toxin was conducted in 2014 [19], regarding the STb toxigenicity. STb is a heat-resistant toxin responsible for diarrhea in farm animals and in humans as well. The toxic effect of STb in host cells is due to allowing the passage of electrolytes and water through the paracellular space. The authors [19] demonstrated that STb could promote the delocalization of transmembrane proteins such as claudin-1.

This event among others can prove how the versatility of this bacterium can reach a worldwide proportion, with a high concern for public health. These types of outbreaks are not solely a consequence of health conditions in developing countries. With the increase in international travel and trade globalization, diarrheagenic *E. coli* has become a worldwide public

On the other hand, antibiotic resistance rates in *E. coli* are rapidly rising, especially concerning to the use of fluoroquinolones and third- and fourth-generation cephalosporin. These strains are acquired predominantly in the community [12]. In these conditions, drug-resistant *E. coli* are readily acquired via the consumption of contaminated food and beverage. Some authors [14] studied 287 *E. coli* samples isolated from meats regarding their virulence factors. They observed that drugresistant isolates had similar characteristics to those collected from the same types of meat.

This review shows the immune view of *E. coli*, and focus on the presence of these bacteria highlighting the acquisition of resistance and discussing various aspects of *E. coli* pathotypes. Because the antibiotic treatment is our primary method of threaten diseases, studies on this field are important to a better understanding of bacterial evasion, circumventing, and

A good immune system is essential for the survival of any organism because of the protection against infectious beings. It is the principal infections evolution blocker that may cause elevated decease rate. This is a well-established fact for almost all known infective illness; the number of subjects in contact with the infectious agents is greater than those who really

Contaminations occurred by no cell invasive bacteria are the most common. In these cases, the immune system of shield is mostly associated to the harborer's innate barriers, natural protection mechanisms, and antibody production. The importance of innate barriers (**Table 1**) in the combat against no cell invasive bacterial infections is well-known [21]. The integrity of skin and mucosa prevent adherence and penetration of bacteria; mucociliary movement eliminates bacteria from the respiratory tract; the stomach's acidic pH destroys some bacteria penetrating by the upper digestive tract; and in the saliva, eyes secretion, and prostatic secretion, lysozyme

subverting mechanisms to acquire resistance characteristics.

and other substances have antimicrobial activity.

gregative *E. coli* (EAEC).

health threat [20].

**2. Immune view**

evolve diseases.

On the other hand, the main characteristic of intracellular bacteria is the ability to survive within the macrophages. In this context, some important pathogens are *L. monocytogenes, Mycobacterium tuberculosis* and, *M. leprae*. Invasion of the macrophage is also a parasite's getaway strategy. Though paradoxical, the last mechanism is benign to the harborer, while the lack of cell penetration by bacteria can induce a strong inflammatory effect and excessive injury to the host.

Adaptive immunity, principally by means of antibodies plays an important function versus bacteria outside of the cell. Antibodies may exert its inhibition in three steps: (i) opsonization, (ii) activation of the complementary system, and (iii) furthering the neutralization of bacteria or their metabolites.

Extracellular bacteria are prone to undoing when phagocytozed. So subverting this system, they developed substances such as evasive mechanism with an antiphagocytic system.

Antibodies directed against these substances not only avoid their action, also facilitate phagocytosis, while neutrophils and macrophages have receivers for the fc part of immunoglobulin (opsonization).

The antibodies also coassist in the destruction of complement by bacteria, and activate this system by the classical pathway. Through neutralization mechanism, IgA antibodies, in particular, can bind to bacteria and therefore prevent the latter from settling on the intestinal mucosa and the respiratory tract. Antibodies bind frequently to toxins produced from bacteria, such as tetanus (*Clostridium tetani*) and diphtheria toxin (*Corynebacterium diphtheriae*), and neutralize the action of these metabolites. The fine balance between health and disease is found in this scenario, in which deficiency is as much as excess may result in tissue damage.
