Poster Presentation Australian Society for Microbiology Annual Scientific Meeting 2023

Acinetobacter vs Acinetobacter: uncovering the molecular mechanisms underpinning intraspecies co-infections with multiple Acinetobacter baumannii strains (#160)

Hannah Lott 1 , Lucie Semenec 1 , Ram Maharjan 1 , Hue Dinh 1 , Alaska Pokhrel 1 , Geraldine Sullivan 1 , Amy Cain 1
  1. ARC Centre of Excellence in Synthetic Biology, School of Natural Sciences, Macquarie University, Sydney, NSW, Australia

Acinetobacter baumannii is one of the leading causes of antimicrobial-resistant (AMR) hospital-associated infections worldwide1. Various antibiotic and biocide resistance determinants, coupled with an innate ability to withstand stress, make A. baumannii extremely difficult to eradicate from both patients and the environment2. Given the ubiquity and persistence of the bacterium within healthcare facilities, ‘intraspecies co-infections’ involving multiple strains of A. baumannii could occur in hospitalized patients, but they are likely underreported3. Furthermore, the technical difficulty of resolving multi-strain bacterial infections using standard laboratory techniques has meant that molecular information on intraspecies co-infection is severely lacking4.

To address this critical research gap, we employed the genome-wide screening technique transposon-directed insertion site sequencing (TraDIS) in A. baumannii, as it is capable of strain-specific resolution. We screened for molecular drivers of intraspecies interactions by competing a dense A. baumannii ATCC 17978 TraDIS mutant library against a range of other A. baumannii strains, including clinical strains of both global clones (AB5075, BAL062) and an environmental (E-072658) isolate.

The TraDIS results revealed essential genes mediating the fitness of ATCC 17978 in intraspecies co-culture, irrespective of the specific strain it was co-grown with, including those encoding Type IV pili and several siderophores. Conversely, several genes encoding components of the Type VI secretion system and quorum sensing system were found to be more important in the clinical pairings. Phenotypic assays assessed growth in biofilm and antibiotic profiling revealed strain-pair specific pairing interactions. We also investigated how strain-specific interactions affect virulence in a host, using the Galleria mellonella in vivo animal model. Significantly fewer larvae co-infected with ATCC 17978 and AB5075 survived compared to those with single strain infections of either strain, suggesting intraspecies interactions are driving increased virulence.

This study provides valuable insight into the dynamics of co-localized A. baumannii strains and builds a solid foundation of knowledge that could facilitate the development of diagnostic tests and treatment strategies for intraspecies co-infections, leading to improved patient outcomes.

  1. 1 Rangel, K., Chagas, T. P. G. & De-Simone, S. G. Acinetobacter baumannii infections in times of COVID-19 pandemic. Pathogens 10, 1006-1019 (2021).
  2. 2 Harding, C. M., Hennon, S. W. & Feldman, M. F. Uncovering the mechanisms of Acinetobacter baumannii virulence. Nature Reviews Microbiology 16, 91-102 (2018).
  3. 3 Orazi, G. & O’Toole, G. A. “It takes a village”: mechanisms underlying antimicrobial recalcitrance of polymicrobial biofilms. Journal of Bacteriology 202, e00530-00519 (2019).
  4. 4 Mäklin, T. et al. Bacterial genomic epidemiology with mixed samples. Microbial genomics 7 (2021).