Molecular Characterization of a Novel Class 1 Integron Containing bla _GES-1 and a Fused Product of aac(3)-Ib/aac(6 " )-Ib " Gene Cassettes in Pseudomonas aeruginosa

Abstract

As seen by the disk diffusion method, the clinical strain of Pseudomonas aeruginosa Pa695, resistant to all extended-spectrum cephalosporins and aminoglycosides, exhibited an unusual synergistic effect between ceftazidime and imipenem. This isolate produced an extended-spectrum ␤-lactamase (ESBL) with a pI of 5.8 that appeared to be chromosomally encoded. Cloning experiments revealed that this ESBL was encoded by bla GES-1 , previously described in an integron from Klebsiella pneumoniae. In P. aeruginosa Pa695, a higher level of resistance to ceftazidime than to ticarcillin was observed, and no synergy between the ␤-lactamase inhibitors and extended-spectrum cephalosporins was detected, in contrast to the resistance pattern observed in K. pneumoniae. Further sequence analysis demonstrated that the bla GES-1 gene cassette was located in a class 1 integron, which contained another sequence corresponding to the fused aac(3)-Ib and aac(6)-Ib gene cassettes. The fusion product was functional, as was the product of each gene cloned separately: AAC(3)-I, despite the deletion of the four last amino acids, and AAC(6), which carried three amino acid changes compared with the most homologous sequence. The AAC(3)-I protein conferred an expected gentamicin and fortimicin resistance, and the AAC(6), despite the Leu-1193Ser substitution, yielded resistance to kanamycin, tobramycin, and dibekacin, but slightly affected netilmicin and amikacin, and had no apparent effect on gentamicin. The fusion product conveyed a large profile of resistance, combining the AAC(6) activity with a higher level of gentamicin resistance without accompanying fortimicin resistance.

Multidrug-resistant Acinetobacter baumannii strains carrying the blaOxA-23 and the blaGES-11 genes in a neonatology center in Tunisia

“…DNA in supernatant was used as a template under standard PCR procedure [9] with a series of different sets of primers. Detection of the known acquired CHDLs (bla OxA-23, bla , and bla OxA-58 ) [14], class A extended-spectrum b-lactamases (bla PER , bla VEB , and bla GES ) [14,15], MBL (bla IMP , bla VIM , bla SIM , bla NDM ) [16,17] and the intrinsic bla OxA-51-like gene was performed as previously described [14].…”

Occurrence of aminoglycoside-modifying enzymes genes (aac(6′)-I and ant(2′′)-I) in clinical isolates of Pseudomonas aeruginosa from Southwest Nigeria.

“…Treatment options for established Pseudomonal infections are always a difficult task due to its problematic multidrug resistance traits 6 . Antibiotic resistance characteristics in P. aeruginosa are both chromosomal and acquired or by horizontal transfer of resistance determinant often carried within plasmids and integrons 7 . Prescriptions for antipseudomonal drugs are combination therapy for effective synergy preventing the development of resistance in the course of treatments 1 …”

Unusual regioversatility of acetyltransferase Eis, a cause of drug resistance in XDR-TB

“…Such multiple acetylation has not been documented for any other known AAC. To confirm the uniqueness of multiacetylation by Eis, we tested six other AACs known to perform monoacetylation at the 2′-, 3-, or 6′ positions (8)(9)(10)(11)(12)(13)(14)(15)(16). UV-Visible (UV-Vis) and mass spectrometry assays of these six AACs with the ten AGs that are multiacetylated by Eis, showed only monoacetylation.…”