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.
ABSTRACT 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.
Article: Survey of molecular determinants in Gram-positive cocci isolated from hospital settings in Argentina.[show abstract] [hide abstract]
ABSTRACT: In order to study the resistance mechanisms to aminoglycosides, tetracyclines and erythromycin, we investigated the genetic determinants on 85 Streptococcus spp., Staphylococcus spp., and Enterococcus spp. isolates collected from 46 hospitals of Argentina over a two-year period. The MICs to amikacin, gentamicin, kanamycin, and streptomycin, tetracycline and erythromycin were determined by the standard broth dilution method according to CLSI recommendations. Detection of resistance genes to the antibiotic tested was assessed by the PCR standard technique whereas the clonal relationships of each species was performed by PFGE. Major heterogeneity was detected in aminoglycoside and erythromycin resistances. Indeed, 37.6% of the isolates harbored the aac(6')-aph(2'') genes; 27% harbored the aph(3')-IIIa and ant(6)-Ia genes along with the aac(6')-aph(2'') gene; 7% carried the ant(4')-Ia gene; and 71% harbored one or more of the erm(A), erm(B), erm(TR), mef(A), mef(E) and msr(A) genes. The tetracycline resistance was determined by the tet(M) gene and was found in 23 isolates that were resistant to this antibiotic. Spreading of tet(M) by the Tn916-like transposon was not a frequent event since the integrase of this element was detected only in 3 Streptococcus spp. isolates. Instead, a 370 bp fragment was detected that corresponded to a region of the CW459-like element integrase in 10 of 11 methicillin-resistant Staphylococcus aureus and in 3 group G Streptococcus isolates, a finding that implies a novel mechanism for tetracycline resistance spreading. This study demonstrates the wide spreading of resistance mechanisms in our nosocomial cocci population and underscores the importance of continuous and efficient epidemiological surveillance.The Journal of Infection in Developing Countries 02/2007; 1(3):275-83. · 1.19 Impact Factor