Current trends in epidemiology and antimicrobial resistance in intensive care units

Intensivecare units (ICUs) have a unique environment within the hospital setting. Thefragility of the patients facilitates the presence of hospital-acquiredinfections (HAIs). To minimize the impact of HAIs, a series of antibioticstewardship strategies including mixing, cycling and combination therapies havebeen developed. Nonetheless, the impact of antibiotic resistance in HAIs inICUs remains extremely high. Most HAIs are caused by multidrug-resistantmicroorganisms, originating from contaminated ICUs surfaces or devices or frompatients admitted for infectious processes. Moreover, antibiotic resistance mayremain occult and be silently introduced into the ICU by a commensal member ofthe microbiomes of patients or health care personnel and thereafter transmittedto a pathogenic microorganism already residing in the ICU. The pathogenicmicroorganisms most frequently residing in ICUs include Escherichia coliand members of the so-called ESKAPE group (Enterococcus faecium,Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii,Pseudomonas aeruginosa and Enterobacter spp.). These microorganismsshow resistance to most of the antibacterial agents commonly used in ICUs andhave been associated with the presence of specific mechanisms of chromosomal ortransferable resistance. Furthermore, when more than one antibiotic-resistantdeterminant is encoded within the same genetic structure lead to the phenomenaof co-selection of resistance. In some cases, ESKAPE microorganisms showresistance to all the scheduled antibacterial agents, requiring the use of“last resort” antibacterial agents such as ceftaroline, colistin ortigecycline. Unfortunately, resistance to all these antimicrobial agents hasbeen reported. The current antibiotic resistance observed in ICUs is of greatconcern and is dramatically advancing to a worrisome end: the return to apre-antibiotic era in which a series of antibiotic-untreatable pan-resistantmicroorganisms colonize ICUs causing severe and deadly infections. Urgentactions to firmly control antibiotic use in all environments are essential toput a halt to or mitigate the development of antibiotic resistance, while thedevelopment of new treatment alternatives is a research priority.