RESISTANCE TO AMINOGLYCOSIDE ANTIBIOTICS AND CONJUGATIVE R PLASMIDS IN SERRATIA MARCESCENS

Abstract

The susceptibility to 11 aminoglycoside antibiotics of 196 clinical isolates of Serratia marcescens was determined and the presence of conjugative R plasmids among the resistant strains was examined. The resistant strains and R plasmids from those strains were detected most frequently in urinary specimens. The percent detection of resistant strains and R plasmids to each antibiotic were as follows.
The resistant strains to ribostamycin and butirosin A were detected at very high frequencies (80-90%), but detection rate of R plasmids was low (15-20%).
The percent detection of resistance to kanamycin A, tobramycin and dibekacin was about 50-60% and that of R plasmids was 14-17% except kanamycin A (44%). Frequency of resistant strains to gentamicin, amikacin and the other three antibiotics (lividomycin A, paromomycin, neomycin B) was moderately low (20-30%) and R plasmids transferring gentamicin resistance were detected in relatively high percentage (40%), however, it was noticed that a small number of strains (2%) carried amikacin resistant plasmids. The resistant strains to sisomicin were isolated at 42% and R plasmids were detected at 28%. It was observed that 67 strains (34%) were multiple resistant for seven or more antibiotics and R plasmids were isolated from these strains at high frequency. It was presumed from resistance pattern of R plasmids that there were many resistant strains involving aminoglycoside phosphotransferase APH (3'). However, it was impossible in many occasions to explain the mechanisms of multiple resistance by a single enzyme.