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

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Abstract

Purpose.

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.

Methodology.

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.

Results.

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.

Conclusion.

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.

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