Table 2.

Sensitivity and selectivity of two chromogenic agars for the isolation of vancomycin-resistant enterococci from 295 stool samples.

	ChromID VRE direct plating Method 1		Brilliance VRE direct plating Method 2		ChromID VRE plating after enrichment Method 3		Brilliance VRE plating after enrichment Method 4
Incubation time (hours)	24	48	24	48	24	48	24	48
Number of plates growing VREa	10	28	14	29	32	33	33	34
Sensitivityb	29%	82%	41%	85%	94%	97%	97%	100%
Number of plates NOT growing organisms other than VREa	292	277	293	285	259	227	280	270
Selectivityc	99%	94%	99%	97%	88%	77%	95%	92%
Number of plates growing Gram-negative organisms	3	10	2	5	28	58	11	18
Number of plates growing Gram-positive organisms	0	6	0	4	6	7	4	6
Number of plates growing yeasts	0	2	0	1	2	3	0	1

VRE = vancomycin-resistant enterococci.

^aTarget VRE organisms consisted of vancomycin-resistant E. faecalis (VREfs) and vancomycin-resistant E. faecium (VREfm).

^bSensitivity was calculated by comparing the number of positive plates for a given method, compared with the cumulative yield of VREfs or VREfm from all four methods (direct plating onto two media, and plating onto both following a pre-enrichment step, n = 34).

^cSelectivity for each method was defined as the number of plates that suppressed the growth of organisms that were not VREfs or VREfm (out of all 295 samples).