VARIABILITY AND EVOLUTION OF THE AADA GENE CASSETTE

GALÁN, ANGÉLICA; QUIROGA, MARIA PAULA; CENTRÓN, DANIELA

Córdoba

Congreso; XI Congreso argentino de microbiología general; 2015

Asociación Civil de Microbiología General

Gene cassettes (GC) are mobile elements associated to horizontal gene transfer inserted inintegrons. The integron/cassettes system allows bacteria to capture and express GC which arepromoterless open reading frames (ORF) with a recombination site called attC. AadA is one of themost widespread resistance GCin the clinic. The aim of this study was to analyze the variability andevolution of both full GC and its individual components, ORF and attC.A search was conducted on INTEGRALL database for different alleles of the aadA GC. Full GCsequences and their individual components were studied through ClustalW and phylogenetic treeswith MEGA 6 program. We made a further study in GenBank database with aadA1 attC GC referencesequence to identify associated GC, and the GC position in different Integrons.We found 37 alleles of aadA from Integrall database. Through the alignment of their attCs sites wefound 18 different sites. As expected, the alignment occurred mainly by the nucleotide bases locatedat the beginning and the end of the sequence of different attCs sites, specifically those designated 1Land 1R, according to consensus sequence (RYYYAAC; GTTRRY R: Purine Y: Pirimidine), which areimportant for recombination. These sequences are not highly modified despite the high diversity ofalleles found in this analysis. In the aadA9 allele, a tandem duplication of 1L was observed. Regardingto 2L and 2R regions (GTTCRARY; RYTYAAC), which are associated to the formation of anextra-helical base, 30 alleles have the consensus sequences, 25 remained with 100% of identity withthe aadA1 attC site. The attC sites in 3 alleles modified their consensus sequences. However, wefound modifications of attC sites in 2 alleles, leading to the loss of the extra-helical base in 2L.The maximum likelihood algorithm tree based on the attC sites evidenced that the predominant attCsite was associated to 12 aadA alleles. This prevalent attC site is included in one cluster together withother 15 attCs sites, while the two remaining attCs sites corresponding to aadA1c and aadA1bq alleleswere found further away from the rest. Trees of full cassettes and ORFs were identical and only havedifferences with the attC sites tree.The location of 200 aadA1 GC was analyzed; we found they were inserted into class 1 or 2 integrons.In class 1 integrons aadA1 was mainly located in the second position within the variable region of theintegron and downstream of dfrA1 GC, but also frequently as the only cassette in the variable region.In class 2 integrons aadA1 was found mostly in third place, also associated to dfrA1 GCand lessfrequently downstream of sat2 or catB8 GCs.The aadA1 GC is highly widespread in class 1 and 2 Integrons. Exchangeable ORF associated to oneattC site and viceversa was a common finding for the aadA GC