Aminoglycoside Resistance Determinants Carrying aacA-aphD Gene in Staphylococci Isolated from Patients in Siriraj HospitalChaisit Niyasom, Amornrut Leelaporn, Pintip Sangsongsilp,Nalinee Aswapokee and Vanchit Gherunpong
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A total of 414 staphylococcal isolates collected from patients in Siriraj Hospital between 1995 and
1997 were examined for resistance to gentamicin (Gm), tobramycin (Tm), kanamycin (Km), neomycin (Nm),
amikacin (Ak) and netilmicin (Nt) by the disk diffusion test and the presence of a transposon Tn4001-related
element/Tn4001-IS257 hybrid structure carrying aacA-aphD gene encoding aminoglycoside resistance, by the
multiplex polymerase chain reaction technique. The studied staphylococci consisted of 100 isolates of methicillinresistant
Staphylococcus aureus (MRSA), 103 isolates of methicillin-sensitive S. aureus (MSSA), 107 isolates of
methicillin-resistant coagulase-negative staphylococci (MRCNS) and 104 isolates of methicillin-sensitive
coagulase-negative staphylococci (MSCNS) classified by mecA PCR assay. Tn4001-related element was detected
in 99% of MRSA but only 0.97% of MSSA; and in 93.46% of MRCNS but only 0.96% of MSCNS. Tn4001-
IS257 hybrid structure was found in only one isolate of MRCNS. All staphylococcal isolates that contained the
Tn4001-related element/Tn4001-IS257 hybrid structure exhibited resistance to Gm, Tm and Km (GmTmKmr)
with the exception of three MRCNS isolates that were resistant to only one or two kinds of those three
aminoglycosides. The strong association between the presence of the Tn4001-related element/Tn4001-IS257
hybrid structure and GmTmKmr indicates that these determinants are, in part if not entirely, responsible for
GmTmKmr in the clinical staphylococcal isolates studied. In addition, 90% of MRSA isolates were resistant to all
drugs tested, whereas only 3% of MRCNS exhibited this resistance pattern. However, the number of resistance
patterns in MRSA was fewer than that in MRCNS.
Keyword:
Aminoglycoside ,Aminoglycoside Resistance , aacA-aphD ,Staphylococci ,Siriraj Hospital , gentamicin ,tobramycin,neomycin,amikacin,netilmicin,MRSA
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