A two-year study of antibiotic resistance in Enterococci isolated from food, abattoirs and farms in Scotland and its link to hospital-acquired infections

Abstract number: 1733_190

Vali L., Hamouda A., Mateus A., Walker D.J., Dave J., Gibb A., Amyes S.G.B.

Objective: To establish whether there is any significant link between enterococci originated from animals and the clinical human strains, indicating animals infecting human populations in hospitals.

Methods: From 2004–2006 a total of 55 different food stuff including dairy and meat products from commercial outlets, 100 faecal samples from cattle on Scottish beef cattle farms, and from abattoirs; 100 faecal, 460 nostril, skin, and ear swab samples collected from pigs, cattle and sheep. Fifty clinical E. faecium and E. faecalis were isolated from hospitalised patients from two hospitals in Edinburgh. Selective media was used for isolation followed by phenotypic and genotypic species characterisations. The minimum inhibitory concentrations of antibiotics were determined by the agar dilution method. PCR and sequencing determined the van genes responsible for vancomycin resistance. Pulsed-field gel electrophoresis (PFGE) was used for molecular typing of the strains, and the presence of esp virulence gene was determined by PCR.

Results: Enterococci were isolated from 20 food, 50 faecal samples, and 27 swab samples. In total 14 strains were resistant to vancomycin, of which 5 were highly resistant to vancomycin (MIC > 32) and teicoplanin (MIC > 16). vanA and vanC1 genes were detected in 10 and 7 strains respectively. PFGE demonstrated that there is diversity within enterococci population isolated from animals and humans; suggesting the host specificity. However closely related clones were identified from outlet food and the clinical strains; suggesting the possibility of contamination by food handlers. esp gene was not detected in enterococci obtained from animal sources.

Conclusion: Host specificity of enterococci suggests that animal strains do not generally impose a serious threat to nosocomial infections in clinical settings. In hospitalised patients the threat of infections is caused by bacteria that largely spread clonally. Moreover the presence of esp gene that identifies the successful nosocomial clones was not detected in any of the strains from the animal origin. Although the presence of van genes causes concern regarding the spread and transfer of vancomycin resistance, it is unlikely that resistance in hospital acquired infections is caused by animal strains. Enterococci may spread from food to humans only if the foodstuff is contaminated through human handling. Safe food handling is therefore crucial especially to high risk patients in hospitals.