title: Role of the acetyltransferase AAC(6')-Iz modifying enzyme in aminoglycoside resistance in Stenotrophomonas maltophilia.
abstract: Stenotrophomonas maltophilia is an emerging nosocomial pathogen that displays high-level intrinsic resistance to multiple antibiotics including aminoglycosides. A gene [aac(6')-Iz] encoding an aminoglycoside-modifying enzyme, AAC(6')-Iz acetyltransferase, was recently cloned and sequenced in S. maltophilia, but its importance with respect to aminoglycoside resistance in this organism was not determined. Using a homologous gene replacement approach, mutants carrying unmarked chromosomal deletions of the aac(6')-Iz gene were constructed in wild-type and in vitro-selected aminoglycoside-resistant S. maltophilia. AAC(6')-Iz-deficient mutants derived from both wild-type and aminoglycoside-resistant strains displayed an increase in susceptibility to amikacin, netilmicin, sisomicin and tobramycin (4- to 32-fold decrease in MICs), known substrates for AAC(6')-I enzymes. The cloned aac(6')-Iz gene restored the aminoglycoside resistance of the aac(6')-Iz mutants, and could also confer aminoglycoside resistance upon Escherichia coli. To assess the significance of the aac(6')-Iz gene with respect to the aminoglycoside resistance of clinical strains, its distribution was assessed in 65 clinical isolates from two hospitals. Using PCR, Southern hybridization, RT-PCR and/or nucleotide sequencing, the aac(6')-Iz gene was identified in 57% of the isolates. Susceptibility tests indicated a good correlation between the presence of the aac(6')-Iz gene and the resistance to tobramycin, netilmicin and sisomicin in these strains. These results indicate that the aac(6')-Iz gene is an important contributor to aminoglycoside resistance in clinical strains of S. maltophilia, particularly to tobramycin.
authors.affiliation: Department of Microbiology and Immunology, Queen's University, Kingston, Ontario, Canada K7L 3N6.
authors.forename: Xian-Zhi
authors.initials: XZ
authors.lastname: Li
authors.forename: Li
authors.initials: L
authors.lastname: Zhang
authors.forename: Geoffrey A
authors.initials: GA
authors.lastname: McKay
authors.forename: Keith
authors.initials: K
authors.lastname: Poole
mesh_terms: D000123:Acetyltransferases / Q000378:metabolism; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D015139:Blotting, Southern; D003001:Cloning, Molecular; D017931:DNA Primers; D004269:DNA, Bacterial / Q000235:genetics; D024881:Drug Resistance, Bacterial; D004926:Escherichia coli / Q000378:metabolism; D005798:Genes, Bacterial; D008826:Microbial Sensitivity Tests; D009154:Mutation / Q000235:genetics; D010957:Plasmids / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D020615:Stenotrophomonas maltophilia / Q000187:drug effects* / Q000201:enzymology / Q000235:genetics*
chemical_list: D000900:Anti-Bacterial Agents; D017931:DNA Primers; D004269:DNA, Bacterial; D000123:Acetyltransferases; C056532:aminoglycoside N(6')-acetyltransferase