Current trends in epidemiology and antimicrobial resistance in intensive care units

Intensive care units (ICUs) have a unique environment within the hospital setting. The fragility of the patients facilitates the presence of hospital-acquired infections (HAIs). To minimize the impact of HAIs, a series of antibiotic stewardship strategies including mixing, cycling and combination therapies have been developed. Nonetheless, the impact of antibiotic resistance in HAIs in ICUs remains extremely high. Most HAIs are caused by multidrug-resistant microorganisms, originating from contaminated ICUs surfaces or devices or from patients admitted for infectious processes. Moreover, antibiotic resistance may remain occult and be silently introduced into the ICU by a commensal member of the microbiomes of patients or health care personnel and thereafter transmitted to a pathogenic microorganism already residing in the ICU. The pathogenic microorganisms most frequently residing in ICUs include Escherichia coli and members of the so-called ESKAPE group (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa and Enterobacter spp.). These microorganisms show resistance to most of the antibacterial agents commonly used in ICUs and have been associated with the presence of specific mechanisms of chromosomal or transferable resistance. Furthermore, when more than one antibiotic-resistant determinant is encoded within the same genetic structure lead to the phenomena of co-selection of resistance. In some cases, ESKAPE microorganisms show resistance to all the scheduled antibacterial agents, requiring the use of “last resort” antibacterial agents such as ceftaroline, colistin or tigecycline. Unfortunately, resistance to all these antimicrobial agents has been reported. The current antibiotic resistance observed in ICUs is of great concern and is dramatically advancing to a worrisome end: the return to a pre-antibiotic era in which a series of antibiotic-untreatable pan-resistant microorganisms colonize ICUs causing severe and deadly infections. Urgent actions to firmly control antibiotic use in all environments are essential to put a halt to or mitigate the development of antibiotic resistance, while the development of new treatment alternatives is a research priority.