Comparison of direct and enrichment methods for the selective isolation of vancomycin-resistant enterococci from feces of pigs and poultry.

Isolation results of vancomycin-resistant enterococci (VRE) of fecal samples from pigs and broiler and layer chickens obtained with two vancomycin-supplemented enrichment media, kanamycin aesculin azide (KAA) broth and Enterococcosel (ECC) broth, and three isolation media, KAA agar, ECC agar, and Slanetz and Bartley (SL) agar, were compared. Direct isolation on vancomycin-containing agar plates was not efficient in swine and layer chickens, which had only low numbers of VRE. In broilers chickens, the VRE content of the samples was high, and SL as well as ECC were found to perform better than KAA agar. The same three agar media were used as selective plating media after 1 and 2 days incubation of the samples in KAA and ECC enrichment broths. Sensitivities of the 12 different enrichment-plate combinations tested ranged from 0 to 81% in layer chickens and from 5 to 44% in samples from pigs. In the high prevalence type of samples from broilers, sensitivities still varied substantially from 52 to 78%. Incubating vancomycin-containing enrichment broths for 2 days compared with 1 day was favorable for the isolation of vancomycin-resistant Enterococcus faecalis, E. gallinarum, and E. casseliflavus but not for E. faecium and E. hirae/E. durans. ECC broth and ECC plates yielded the highest number of E. gallinarum and E. casseliflavus. In layer as well as in broiler chickens, ECC broth incubated for 2 days and plated on ECC agar was the most sensitive method. In pigs, however, KAA broth incubated for 2 days and plated on ECC medium yielded the highest number of VRE.