Acinetobacter baumannii: A Dangerous Pathogen Emerges

Acinetobacter baumannii: A Dangerous Pathogen Emerges By Peter C. Iwen, PhD, Associate Director, NPHL Acinetobacter baumannii is considered the most common oxidase-negative non-fermenting gramnegative rod encounter in the clinical laboratory [1]. This organism is widely distributed in nature and in the hospital environment and generally considered an opportunistic pathogen in debilitated patients. Recently, the Infectious Diseases Society of America included this microbe on a hit list of the six top priority dangerous drug-resistant microbes (see Table 1) due to the propensity of this organism to develop drug-resistance and to the lack of development of new drugs to treat infections caused by resistant A. baumannii [2]. Resistance of A. baumannii to carbapenems (Imipenem), which is the drug of choice to treat serious infections caused by this species, are fast becoming more common in the laboratory. The NPHL has lately observed multi-drug resistant A. baumannii from multiple laboratories within Nebraska. This bacterium is one of 17 recognized species within the genus Acinetobacter. Many of the species within this genus are difficult to separate reliably by phenotypic methods alone and frequently are placed into groups or complexes based biochemical test results. It is therefore not uncommon to identify an isolate as A. baumannii/calcoaceticus complex or A. baumannii/haemolyticus All of these species have the ability to oxidize glucose and are therefore described as the saccharolytic species of Acinetobacter in contrast to the asaccharolytic species which is most commonly A. lwoffii. Table 2 identifies some simple phenotypic observations that can be used to separate these common species following automated system identification. A. baumannii is considered by far the most common species isolated from human specimens followed by A. lwoffii and A. haemolyticus [1]. To monitor for the emergence of resistance within A. baumannii in Nebraska, laboratories are being asked to submit to the NPHL any multi-drug resistant isolates of this species that are encountered. These isolates can be submitted through the current courier system that is now used for the submission of other clinical isolates for epidemiological evaluation. Any results following the evaluation of these isolates will be communicated with the laboratories in a future newsletter. Contact Peter Iwen at 559-7774 for further information concerning this issue. References 1. Schreckenberger, P.C., et al. 2003. Acinetobacter, Achromobacter, Chryseobacterium, Moraxella, and other nonfermentative gram-negative rods, pg 749-779. In P.R. Murray et al. (ed.), Manual of Clinical Microbiology, Volume 1. 8th Edition, ASM Press, Washington, DC. 2. Talbot, G.H., et al. 2006. Bad bugs need drugs: an update on the development pipeline from the Antimicrobial Availability Task Force of the Infectious Diseases Society of America. Clin Infect Dis. 42: 657-668.