[New inactivating enzyme of aminoglycoside antibiotics produced by genes on R-plasmid of Serratia spp. and nosocomial infection].

Though incident due to Serratia spp. has decreased with the use of third generation cephems, S. marcescens with multiple drug resistance are still clinically occasionally isolated S. marcescens strains 218, 219 and 220 we isolated clinically, were found to possess aminoglycoside inactivating enzyme activities which had not been expected to exist in Serratia spp. These isolates inactivated aminoglycoside antibiotics except strains 218 and 219 were sensitive to isepamicin whereas strain 220 was sensitive to isepamicin and gentamicin. It was found that strains 218 and 219 possessed aminoglycoside inactivating enzyme AAC(2'), and strain 220 AAC (6'). The genes coding for these inactivating enzymes were found to be on R-plasmid and transferred between bacterial cells. Frequencies of transfer of the R-plasmid from Serratia to Escherichia coli chi-1037 were be low, but the transfer definitely occurred as frequencies of 4.3 x 10(-7) from strain 218, 5.2 x 10(-7) from strain 219, and 8.3 x 10(-7) from 220 were determined. To prevent nosocomial infections, the eradication of multi-resistant Serratia strains is strongly recommended when they are isolated even apparent symptoms of infections are not observed.