Abstract

The molecular epidemiology of the aacC1, aacC2, aacC3, and aacC4 genes encoding aminoglycoside acetyltransferases AAC(3)-I, AAC(3)-II, AAC(3)-III and AAC(3)-IV, respectively, was studied by KNA hybridization and polymerase chain reaction (PCR). One hundred twenty six moderate-level (MICs>20 ㎍/ml) and 153 high-level (MICs>2,000 ㎍/ml) gentamicin resistant strains were collected from stream water and hospital sewage. Resistant strains were screened by dot-blot hybridization for the presence of the gene encoding aminoglycoside-(3)-N-acetyl-transferase II (aacC2). The aacC2 probe hybridized with 5.4%(3/56) of the moderate-level resistant strains from stream water and 18.6% (13/70) of the strains from hospital sewage, and with 87.6% (134/153) of the high-level resistant bacteria. The presence of the genes for AAC(3)-I,-III and-IV in the strains was studied by polymerase chain reaction. The most common gene among the moderate-level resistant stratins was aacC4, in 8.9% (5/56) of the stream water strains and in 24.3%(17/70) of the hospital sewage strains, and followed by aacC3 gene, in 5.4% (3/56) and in 20.0% (14/70) of the tested strains, respectibely. None of the 126 isolates with moderate-level resistance amplified the expected DNA fragment of aacC1 gene. In contrast, 11.8% (18/153) of the high-level resistant isolates contained aacC1 gene. The frequency of aacC3 gene in the high-level resistant strains was 19.6% (30/153) while that of aacC4 was 11.1% (17/153).

• Keywords: aacC1; aacC2; aacC3; aacC4; aminoglycoside acetyltransferase; gentamicin resistance.