**1.7. Consequences of infection by MRB**

The prognosis of MRB infections is not good, with an increase in hospital stay, mortality and economic costs [12]. These types of infections are usually resistant to empirical therapies, which implies a delay in starting the correct antibiotic treatment. Also derived from this, the use of second line treatment with lower bactericidal capacity and less favorable pharmodynamic/pharmacokinetic profile contributes to a higher incidence of adverse events. At times, a greater virulence of these germs has been described.

#### **1.8. Colonization and infection**

The difference between these two terms lies in the simple presence (colonization) or clinical involvement (infection). The oropharynx is colonized early by hospital flora, especially GNB, in critically ill patients. The risk of colonization increases with hospital stay and severity. In the same way, the administration of antibiotics systemically increases the risk of acquiring the carrier state. Patients with APACHE II greater than 20 are usually carriers of abnormal flora such as GNB and MRSA. The passage from colonization to infective germs is defined by the rupture of the natural defense mechanisms (neutropenia, immunosuppression), the pathogenicity of the germ itself, alteration of the intestinal flora by antibiotic therapy previously administered. Altered mechanisms of clearance of germs are suggested. A necessary factor for the development of the infection is the overgrowth; 20–40% of carrier patients develop an infection, so those carriers must be actively identified when we want to control an outbreak of infection by resistant flora.
