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Mahbub Alam M, Kobayashi N, Ishino M, Sumi A, Kobayashi K, Uehara N, Watanabe N: 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. Microb Drug Resist. 2005 Fall;11(3):239-47.
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. |
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