Evolutionary and dissemination aspects that explain the current architecture of class 2 integrons

MASSÓ MARIANA; PIEKAR MARIA; RAMIREZ MARIA SOLEDAD; ALVAREZ VERÓNICA ELIZABETH; QUIROGA MARIA PAULA; ALONSO CARLA ANDREA; TORRES CARMEN; CENTRÓN DANIELA

Viena

Congreso; 27th European Congress of Clinical Microbiology and Infectious Diseases (ECCMID); 2017

Background: Among the universe of integrons, class 1 and 2integrons are the most common in the nosocomial niche since they are directlyinvolved with the increase of antibiotic multidrug resistance around the world.However, several differences have been highlighted among both classes ofintegrons: i) the dissemination is species dependent for class 2 integrons, ii)while intI1 is embedded in transposon Tn402, intI2 is embedded in transposonTn7, iii) while there are a variety of gene cassettes arrays in the variableregion of class 1 integrons, this is not the case for class 2 integrons. Sinceseveral studies have focused on the origin and evolution of class 1 integrons, here, the overall objective was to investigate howclass 2 integrons disseminated before the antibiotic era and the ways thatallowed them to be later successful in the nosocomial niche. Material/methods: We performed both experimental and bioinformaticsstudies searching for the association of the intI2 type gene and the transposonTn7. We investigated in 16 strains from our laboratory that did not possess anyof the 5 genes of Tn7 transposition. We searched in GenBank database for intI2alleles and tns A,B,C,D,E genes in order to study the association between class2 integrons and transposon Tn7. For intI2 genes, we performed a globalalignment with Clustal-W and then obtained their phylogenetic relationshipsusing the Maximum Likelihood test with MEGA 7.0 software and intI1, intI3 andXerC as possible outgroups. After obtaining the topology, we proceeded in thesame way with tns genes, when present in the same Genbank record. Finally, weinferred evolutionary aspects that explain class 2 integrons architecture withTn7 dissemination. Results: Tn7L primers for the region left side of the inverted repeats of Tn7,with primer intI2F in a PCR reaction, produced an amplicon of 1250 bp,denominated In2-7::Tn7.The strains from our laboratory analysed for this PCRwere from the clinic, from wild mouse and from sites with low anthropic impact.5 Acinetobacter baumannii, 1 Escherichia coli, from the clinic, 9Proteus spp. from wild mouse, and 1 Pseudomonasfraggi from Tierra del Fuego, Argentina. The amplification reaction waspositive in all strains, including the E.coli strain possessing a putative functional intI2 allele. 41 intI2 geneswere found on GenBank and categorized in 9 different alleles, including somenovel uncharacterized intI2 alleles. The 80% had a non sense mutation renderinga premature stop codon on position 535 (CàT) with respect to a functional allele (Glutamine à stop) and the other 20% were functional. The 58% ofclass 2 integrons were adjacent to tns A-E genes. Within each category, the tnsgenes were fully conserved but not always present. 22/41 had the 28 bpimperfect IR of Tn7. One third of these class 2 integrons were next to gmlSgene. The geographical distribution of these alleles was worldwide.Conclusions: Inti2 gene was found associated with was found inintegrons that were sometimes not embebbed in Tn7.