Crucial role of the accessory genome in the evolutionary trajectory of Acinetobacter baumannii International Clone 1.

ALVAREZ, VERÓNICA ELIZABETH; ELISABET VILACOBA; CENTRON DANIELA; MARÍA PAULA QUIROGA; QUIROGA CECILIA; GALAN ANGÉLICA; RAMÍREZ MARÍA SOLEDAD

Frontiers Microbiology

Frontiers

Lugar: Lausanne; Año: 2020 vol. 11

Acinetobacterbaumanniiis one of the most important nosocomial pathogens with high genomic plasticityable to develop extensively antimicrobial resistance (XDR). The role ofaccessory genome in the success of the international clone 1 (IC1) has been partiallystudied. A144 and A155 isolated from the same hospital and 6 complete IC1genomes from different geographical regions isolated 26 years apart were usedfor genomic and biological studies. Although four inversions, 378 insertions,and 433 deletions were identified when A144 was compared to IC1 genomes, a highdegree of synteny was observed as a main difference with other high-risk IC2,IC3, IC113 and sporadic clones of A.baumannii. Some genetic traits related to accessory genome were foundcommon and exclusively within IC1 genomes, denoting acquisition before clonaldiversification such as two novel regions of genome plasticity (RGP), genesencoding AdeABC, AdeIJK, and AdeFGH efflux pumps aswell as an identical CRISPR-Cas system located in the same IC1 loci. Althoughidentified as hot spot for recombination, other blocks of accessory genome werepreserved in IC1 genomes with several signs of microevolution such as theAbaR0-type genomic island identified in A144 which was maintained at least over831 generations in three independent experiments without antimicrobialpressure. Interestingly, the Insertion Sequences (IS) identified in IC1 genomesshowed to adapt to the changing habitats without maintenance of the genomiclocation nor of the type of mobile element. Taken together, these findingssuggested that preservation of some genetic blocks of accessory genome, as wellas the preservation of synteny of genomes from different continents along time andIS plasticity may be central features of the genomic structure for the success andadaptation of this high-risk clone. Also, competition of A144 versus A118 withoutantimicrobial pressure suggested a greater ability of IC1 to grow over theclones with a sporadic behavior of A.baumannii, which explains in part, from an ecological perspective, theglobal achievement in the hospital habitat of this successful pandemic clone.