Occurrence of Aminoglycoside Modifying Enzymes (AMEs) among Isolates of Escherichia coli Exhibiting High Levels of Aminoglycoside Resistance Isolated From Korean Cattle Farms

Abstract

This study investigated 247 Escherichia coli isolates collected from four cattle farms to characterize aminoglycoside-modifying enzyme (AME) genes, their plasmid replicons and transferability. Out of 247 isolates a high number of isolates (total 202; 81.78%) were found resistant to various antibiotics by disc-diffusion. Of the 247 strains 139 (56.3%) were resistant to streptomycin and other antibiotics resistance followed as tetracycline (12.15%), ampicillin (7%), chloramphenicol (5.7%) and trimethoprim-sulfamethoxazole (0.8%). Among 247 isolates B1 was the predominant Phylogenetic group identified, which makes up 151 isolates (61.1%), followed by group A (27.9%), D (7%) and B2 (4%). Out of 139 isolates investigated for AME, 130 (93.5%) isolates carried at least one AME gene. aph3''-1a and aph3''-1b (46%) were the principal genes detected, followed by aac3-IVa (34.5%). ant2''-1a was the least detected gene (2.2%). 9 (6.5%) strains carried no AME genes. 12 (63.2%) among 19 isolates transferred AME gene to a recipient and aph3'-1a was the dominant transferred gene. Transferability mainly occurred via the IncFIB replicon-type (52.6%). Pulsed-field gel electrophoresis (PFGE) typing demonstrated a higher degree of diversity with 14 distinct cluster types. This result suggests commensal microflora from food-producing animals has a tremendous ability to harbor and transfer AME genes, and poses potential risk by dissemination of resistance to humans through food-chain.

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