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

Isolation results of vancomycin-resistant enterococci (VRE) of fecal sample s from pigs and broiler and layer chickens obtained with two vancomycin-sup plemented enrichment media, kanamycin aesculin azide (KAA) broth and Entero coccosel (ECC) broth, and three isolation media, KAA agar, ECC agar, and Sl anetz 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 K AA agar, The same three agar media were used as selective plating media aft er 1 and 2 days incubation of the samples in KAA and ECC enrichment broths. Sensitivities of the 12 different enrichment-plate combinations tested ran ged 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 enric hment broths for 2 days compared with 1 day was favorable for the isolation of vancomycin-resistant Enterococcus faecalis, E. gallinarum, and E. casse liflavus but not for E. faecium and E. hirae/E. durans. ECC broth and ECC p lates 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 pl ated 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 o f VRE.