Detection of a novel aph(2") allele (aph[2"]-Ie) conferring high-level gentamicin resistance and a spectinomycin resistance gene ant(9)-Ia (aad 9) in clinical isolates of enterococci.
Aminoglycoside-modifying enzymes (AMEs) are major factors that confer aminoglycoside resistance to enterococci. In an epidemiologic study on distribution of 12 AME genes in 534 recent clinical strains isolated from a Japanese hospital, two uncommon AME genes, ant(9)-Ia and a novel aph(2") allele, aph(2")-Ie, were detected. ant(9)-Ia had been reported only in Staphylococcus aureus and encodes spectinomycin adenylyltransferase ANT(9)-I, which confers resistance to spectinomycin. The ant(9)-Ia gene was detected in three strains, a single strain each of Enterococcus faecalis, E. faecium, and E. avium. Nucleotide sequences of ant(9)-Ia from these three enterococcal species were identical to that reported for S. aureus and considered to be located on Tn 554. The new aph(2") allele, designated aph(2")-Ie, was identified in three E. faecium strains. The aph(2")-Ie allele was genetically close to aph(2")-Id reported in E. casseliflavus (93.7% amino acid sequence identity; 96.3% similarity), while distant from aph(2")-Ia, aph(2")-Ib, or aph(2")-Ic (26.3-29.5% amino acid sequence identity). Sequence divergence between APH(2")-Id and APH(2")-Ie was mostly located in amino-terminal half. In contrast, sequences corresponding to the three motifs required for aminoglycoside phosphotransferase were conserved except for a single amino acid. Three E. faecium strains having aph(2")-Ie showed high-level resistance to gentamicin and streptomycin, but not to kanamycin, dibekacin, and tobramycin, unlike enzyme specificity described for aph(2")-Id in E. casseliflavus. Such a difference in resistance phenotype was suggested to be related to amino acid sequence divergence between APH(2")-Id and APH(2")-Ie.
Mahbub Alam
Mohammed
M
Department of Hygiene, Sapporo Medical University School of Medicine, Sapporo 060-8556, Japan.
Kobayashi
Nobumichi
N
Ishino
Masaho
M
Sumi
Ayako
A
Kobayashi
Ken-Ichiro
K
Uehara
Nobuyuki
N
Watanabe
Naoki
N
D000483:Alleles; D000617:Aminoglycosides / Q000494:pharmacology; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics*; D024881:Drug Resistance, Bacterial / Q000235:genetics*; D016983:Enterococcus / Q000187:drug effects* / Q000201:enzymology / Q000235:genetics; D005839:Gentamicins / Q000494:pharmacology*; D006801:Humans; D010770:Phosphotransferases / Q000378:metabolism; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000235:genetics*; D000198:Spectinomycin / Q000494:pharmacology*
D000617:Aminoglycosides; D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D005839:Gentamicins; D000198:Spectinomycin; D010770:Phosphotransferases; C112789:APH(2'')-Id protein, Enterococcus; D017853:Phosphotransferases (Alcohol Group Acceptor)