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Distribution of resistance determinants and mobile elements involved in horizontal genetic transfer in clinical isolates of Achromobacter spp

Authors

Abstract

Achromobacter spp. are gram-negative (gn) bacilli widely distributed in nature including the healthy human gastrointestinal tract. However, they are opportunistic nosocomial and community pathogens with A. xylosoxidans being the species most commonly associated with infection. Numerous cases of A. xylosoxidans infections are documented in immunocompromised and cystic fibrosis patients. In Argentina, the frequency of A. xylosoxidans has been increasing and it accounts for 6.6 % of total non-glucose-fermenting gn bacilli infection isolates. Although clinical Achromobacter spp. isolates usually show multiple drug resistance, the low attention paid to this pathogen resulted in poor understanding of their resistance mechanisms. To gain insights into the genetic characteristics of the resistance determinants, 30 non-epidemiological Achromobacter spp. clinical isolates from Argentina were studied to detect and characterize genetic elements associated with drug resistance. Isolates were identified using standard biochemical tests, the API 20NE kit (Biomeriux), and sequencing the 16S rRNA gene. R plasmids (IncP, IncW, IncA/C, IncN, IncFII), transposons or insertion sequences (IS) (Tn1331, Tn3, Tn7, IS26, IS1999, IS440) associated to resistance to antibiotics commonly used in our hospitals, and class 1 and 2 integrons were detected by PCR using specific primers and total DNA as template. There was a high prevalence of A. xylosoxidans (27/30) and the clonal relationships analysis using the macrorestriction technique showed the presence of 15 different clones among the 27 A. xylosoxidans isolates. Class 1 and class 2 integrons were detected in 10 and 3 of the isolates, respectively. Their variable regions were characterized by PCR cartography. IS26 and IS440 were found in 2 and 7 isolates, respectively and IncP plasmids, usually wide host range, self-transmissible, and possessing antibiotic resistance genes, were identified in 10 isolates. In total 18 of the 30 Achromobacter spp. isolates were positively identified as carriers of at least one of these genetic elements that are commonly associated to the presence and transfer of resistance genes. These results support the hypothesis that Achromobacter spp. is becoming a reservoir of resistance determinants associated to horizontal gene transfer in gn bacteria and could become a problematic causative agent of hospital infection.

Keywords

antibiotic resistance, opportunistic infections, mobile genetic elements