MOLECULAR EPIDEMIOLOGY OF AMINOGLYCOSIDE RESISTANCE IN ACINETOBACTER SPP

Most aminoglycoside resistance in Acinetobacter spp. involves producti on of aminoglycoside-modifying enzymes. Previous studies have shown th at the genes encoding these enzymes can be present on plasmids, transp osons or within integron-type structures. To determine whether particu lar mechanisms of aminoglycoside resistance have developed in strains from specific geographical locations (with subsequent clonal spread), or whether common mechanisms have been acquired by genotypically disti nct clinical isolates of Acinetobacter spp. throughout the world, a ge notypically heterogeneous collection of 24 multiresistant clinical iso lates of Acinetobacter spp. from 15 hospitals in 11 countries worldwid e was studied. All were resistant to two or more aminoglycoside antibi otics. The full aminoglycoside resistance profile was determined for e ach isolate, allowing a putative enzyme content to be inferred, with s ubsequent confirmation of enzyme content and genetic location by polym erase chain reaction (PCR) and hybridisation techniques. All produced at least one aminoglycoside-modifying enzyme, most commonly AAC(3)-I a nd ANT(3 '')-I in various combinations. Other enzymes found were AAC(3 )-II, AAC(6')-I, ANT(2 ''), APH(3')-I and APH(3')-VI. None was confine d to strains from a particular geographical area. Nine isolates transf erred resistance mediated by AAC(3)-I, ANT(2 '')-I, APH(3 '')-I or APH (3)'-VI by conjugation to a sensitive strain of A. baumannii, but most resistance was non-transferable. PCR mapping revealed an integron loc ation in six isolates for the aac(3)-Ia gene and in three isolates for the ant(3 '')-Ia gene. Overall, the study demonstrated that similar a minoglycoside-modifying enzymes are found in unrelated isolates of Aci netobacter spp., and that particular genes are not restricted to speci fic areas of the world. The demonstration of certain genes on plasmids and integrons emphasises the probable importance of these structures in the dissemination of certain types of aminoglycoside resistance in Acinetobacter spp.