Posts tagged: Acinetobacter infection

Acinetobacter infection is a rare and serious bacterial disease acquired by combat troops returning from conflict zones in areas of the Middle East (Howard et al., 2012). In addition, Acinetobacter infection occurs in intensive care unit (ICU) patients who are critically ill or have a weakened immune system (CDC, 2010). The disease can initially manifest as nosocomial pneumonia, bloodstream or wound infection, urinary tract infection, or other type of opportunistic infection. Across the range of anatomical regions which may be involved, Acinetobacter infections are typically associated with worse outcomes compared with more commonly isolated organisms. For example, ventilator associated pneumonia (VAP) is defined as occurring for more than 48 hours following mechanical ventilation in an intubated patient, and accounts for 86% of all nosocomial pneumonias. VAP caused by Acinetobacter is associated with mortality rates up to 70% and greater disease severity than other etiologies (Howard et al., 2012; Koenig et al., 2006). Acinetobacter infections also account for 1.3% of all nosocomial bloodstream infections in the US and are associated with the third highest mortality rate in the ICU below Pseudomonas infection and Candidiasis.

Normally found in aquatic environments, Acinetobacter can be found in cultures of hospitalized patients’ sputum, respiratory secretions, wounds, and urine, but normally has low virulence (Cunha, 2016; Howard et al., 2012). The genus Acinetobacter includes a heterogeneous group of 34 formally named species of aerobic nonhemolytic Gram-negative coccobacilli, which are usually found in diploid formation or chains of variable length. Among the Acinetobacter species, A. baumannii, A. pittii, and A. nosocomialis are closely related and are considered important nosocomial pathogens accounting for most Acinetobacter infections (Kim et al., 2014). Of these, Acinetobacter baumannii accounts for 80% of reported infections (CDC, 2010).

A. baumannii is a Gram-negative, pleomorphic, aerobic, catalase-positive, oxidase-negative, non-motile, non-fermenting coccobacillus. Carbapenem-resistant Acinetobacter baumannii (CRAB) refers to strains of this pathogen which have reduced susceptibility to carbapenems due to a variety of mechanisms including expression of a carbapenemase enzyme, porin loss and/or changes in membrane permeability (Codjoe et al., 2018). This activity contributes to the high frequency of multidrug-resistance (MDR) and the high severity of infections caused by CRAB (Queenan et al., 2007). The incidence of MDR properties among all A. baumannii infections is estimated from 30-80% of reported cases (CDC, 2011; Xiao et al., 2017).

References

CDC. (2010). Acinetobacter in Healthcare Settings. Retrieved from https://www.cdc.gov/hai/organisms/acinetobacter.html

CDC. (2011). Gram-negative Bacteria Infections in Healthcare Settings. Retrieved from https://www.cdc.gov/hai/organisms/gram-negative-bacteria.html

Codjoe, F. S., & Donkor, E. S. (2018). Carbapenem Resistance: A Review. Medical Sciences, 6(1), 1.

Cunha, B. (2016). Acinetobacter. Retrieved from https://emedicine.medscape.com/article/236891

Howard, A., O’Donoghue, M., Feeney, A., & Sleator, R. D. (2012). Acinetobacter baumannii: an emerging opportunistic pathogen. Virulence, 3(3), 243-250. doi:10.4161/viru.19700

Kim, U. J., Kim, H. K., An, J. H., Cho, S. K., Park, K.-H., & Jang, H.-C. (2014). Update on the Epidemiology, Treatment, and Outcomes of Carbapenem-resistant Acinetobacter infections. Chonnam medical journal, 50(2), 37-44. doi:10.4068/cmj.2014.50.2.37

Koenig, S. M., & Truwit, J. D. (2006). Ventilator-associated pneumonia: diagnosis, treatment, and prevention. Clinical microbiology reviews, 19(4), 637-657. doi:10.1128/CMR.00051-05

Queenan, A. M., & Bush, K. (2007). Carbapenemases: the versatile beta-lactamases. Clinical microbiology reviews, 20(3), 440-458. doi:10.1128/CMR.00001-07

Xiao, D., Wang, L., Zhang, D., Xiang, D., Liu, Q., & Xing, X. (2017). Prognosis of patients with Acinetobacter baumannii infection in the intensive care unit: A retrospective analysis. Experimental and therapeutic medicine, 13(4), 1630-1633. doi:10.3892/etm.2017.4137

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