Acinetobacter species: Resistance update and treatment options

Multidrug-resistant (MDR) Acinetobacter baumannii has been reported worldwide and is now recognized to be among the most difficult antimicrobial-resistant Gram-negative bacilli (GNB) to control and treat. While definitions of antimicrobial resistance vary in the literature, increasing antimicrobial resistance among isolates of Acinetobacter has been clearly documented. The organism is a rapidly emerging pathogen in the healthcare setting, where it causes healthcare-associated infections including bacteremia, pneumonia, meningitis, urinary tract infections, and wound infections. Properties of A. baumannii, such as its ability to survive under a wide range of environmental conditions and to persist for extended periods of time on environmental surfaces, make it a frequent cause of outbreaks as well as an endemic pathogen in the healthcare setting. Risk factors for colonization or infection with A. baumannii include prolonged length of hospital stay, exposure to intensive care units (ICUs) and mechanical ventilation, antimicrobial use, recent surgery, invasive procedures, and underlying severity of illness. An increase in the level of antimicrobial resistance greatly limits the therapeutic options for patients infected with this organism, especially when isolates are resistant to the carbapenem class of antibiotics. Carbapenems remain the treatment of choice when isolates are susceptible and colistin has made a resurgence for use against MDR-Acinetobacter infections that have developed high-level resistance to all other conventional agents. Even though some data support the use of sulbactam, rifampin, and tigecycline, the available literature cannot provide clear answers about these agents as therapeutic options due to lack of controlled clinical studies. Furthermore, it is not clear if combination therapy is more effective than monotherapy. These uncertainties and the lack of therapeutic options make infection control measures and prevention strategies that are effective for controlling transmission of antimicrobial-resistant Acinetobacter essential.