Characterization of high level ampicillin- and aminoglycoside-resistant enterococci isolated from non-hospital sources.

Abstract

High level ampicillin- and aminoglycoside-resistant enterococci are being increasingly reported from non-hospital sources. This study was carried out to characterize these strains from non-hospital sources in Nigeria. A collection of Enterococcus faecium isolated from vegetables, soil, farm animals and manure and observed to be resistant to ampicillin (n=63) and gentamicin (n=37) discs, were screened for resistance to high levels of ampicillin and aminoglycoside using E-test strips. Putative high level ampicillin- and aminoglycoside-resistant strains were screened for pbp5 and aminoglycoside modifying enzyme genes, respectively, by PCR. The C-terminal region of the amplified pbp5 gene was also sequenced. Five (5/63) and thirty-five (35/37) of the ampicillin- and aminoglycoside-resistant strains were identified as high level ampicillin- and aminoglycoside-resistant E. faecium strains, respectively, based on the MIC results. The amplified pbp5 gene from the high level ampicillin-resistant isolates displayed 96-99 % nucleotide sequence similarity with the reference strains and three novel insertions (500Glu→Leu, 502Asp→Arg and 614Ile→Phe) in the amino acid sequence. Aminoglycoside modifying enzyme genes aac(6')-Ie-aph(2″) (100 %), aph(2')-Ic (88.8 %), aph(3')-IIIa (90 %) and ant(4')-Ia (40 %) were detected among the high level aminoglycoside-resistant isolates. This is the first report on the characterization of high level ampicillin- and aminoglycoside-resistant Enterococcus faecium among animals and vegetables in Nigeria. The results show that non-hospital sources can constitute a reservoir for potential dissemination of these strains and genes to humans via the food chain or by direct contact.