Acinetobacter baumannii is an opportunistic nosocomial pathogen that is classed by the WHO as a “critical” priority pathogen requiring new antibiotic development, but the evolution of multi-drug and pan-drug resistant isolates, and its ability to persist in adverse environments, highlight the need for a new type of therapeutic. One strategy is to target small regulatory RNAs (sRNAs), which in many bacteria are crucial in post-transcriptional regulation of important biological processes. However, knowledge of sRNAs in A. baumannii is limited, thus additional information is crucial to the development of new therapies.
RNA-seq analysis of A. baumannii strain, ATCC17978, cultured in vitro compared to in vivo indicated that sRNA ABBFAs_076 had one of the most significant differential expression ratios, which implied functional significance. This work has applied this finding to the modern clinical isolate, AB307-0294. sRNAs exert their control by interacting with specific mRNAs or proteins, resulting in an adaptive change. Using MS2 aptamer affinity purification with MS2-tagged ABBFAs_076 (MS2-76), we identified 227 transcripts that were associated with MS2-76. In particular, mRNA from the gatA_2, fadD32 and paa operons were of interest, as these genes were also differentially expressed in an ABBFAs_076 overexpression RNA-seq dataset. Interactions between ABBFAs_076 and the mRNA of genes from these operons were verified using a 2-plasmid sf-gfp translational fusion reporter system. Phenotypic analysis showed that overexpression of ABBFAs_076 resulted in altered swarming motility and indole-3-acetic acid (IAA) catabolism, which were consistent with the regulation of the fadD32 and gatA_2 operons by ABBFAs_076, respectively. The alteration to IAA catabolism resulted in downstream stress tolerance effects, such as enhanced oxidative stress resistance and survival in the presence of human neutrophils.
These data provide evidence that ABBFAs_076 is involved in the regulation of biological processes that facilitate persistence in the host and contributes to the overall pathogenesis of A. baumannii.