Insights Into Mechanisms of Biofilm Formation in Acinetobacter baumannii and Implications for Uropathogenesis

Abstract

Multidrug resistant Acinetobacter baumannii is a serious healthcare threat. In fact, the Center for Disease Control recently reported that carbapenem-resistant A. baumannii is responsible for more than 8,500 infections, 700 deaths, and $281 million in healthcare costs annually in the United States with few, if any, treatment options available, leading to its designation as a pathogen of urgent concern and a priority for novel antimicrobial development. It is hypothesized that biofilms are, at least in part, responsible for the high prevalence of A. baumannii nosocomial and recurrent infections because they frequently contaminate hospital surfaces and patient indwelling devices; therefore, there has been a recent push for mechanistic understanding of biofilm formation, maturation and dispersal. However, most research has focused on A. baumannii pneumonia and bloodstream infections, despite a recent retrospective study showing that 17.1% of A. baumannii isolates compiled from clinical studies over the last two decades were obtained from urinary samples. This highlights that A. baumannii is an underappreciated uropathogen. The following minireview will examine our current understanding of A. baumannii biofilm formation and how this influences urinary tract colonization and pathogenesis.

Keywords: Acinetobacter baumannii; CAUTI; bacterial biofilm; environmental sensing; gene expression; uropathogen; virulence.

Figure 1

Functional categorization of corroborated genes up-regulated in biofilms. Each stacked bar represents the number of corroborated genes confirmed by transcriptional, proteomic, transcriptional and proteomic data sets (as listed in Table 1). The last stacked bar represents the number of genes confirmed in at least two different strains of A. baumannii regardless of data set. The total number of genes compared in each data set are listed after the bar title (i.e., 473 up-regulated transcripts compiled and compared, 381 up-regulated proteins compiled and compared, and so on). Each stacked bar is further broken down into functional subcategories: outer membrane proteins (blue), adhesion and motility (orange), metabolism (gray), transcription (yellow), translation (purple), and hypothetical proteins (green).