Table 3. Differentiation of mixed cultures of E. coli serovars from food samples on SMAC agar based on scatter pattern.

Bacterial/Food samplea	No. of colony analyzed	No. of positive colony with BARDOT Libraryb		No. of positive colony with serovars-specific PCRc		Identification accuracy (%)d
		O26	O157	O26	O157
E. coli O26 & O157 tested as mixed culture	30	15/30	15/30	15/30	14/30e	96.6
Lettuce with E. coli O26	6	6/6	0/6	6/6	0/6	100.0
Lettuce with E. coli O157	6	0/6	6/6	0/6	6/6	100.0
Lettuce with E. coli O26 & O157	12	6/12	6/12	5/12	7/12	96.6
Ground beef with E. coli O26 & O157	14	7/14	7/14	7/14	7/14	100.0

^aLettuce and ground beef samples were inoculated with 10²CFU/25g of each E. coli O26 and E. coli O157 cells

^b E. coli colonies grown on SMAC agar for 10–11 h were matched with BARDOT library containing multiple standard strains of O157 STEC and non-O157 STEC.

^c E. coli serovar (O26 and O157) specific primers were used in multiplex PCR (mPCR). Prior to food sample analysis primers were validated for specificity with three standard strains of each E. coli O157:H7 and O26:H11. Primer sequences were adapted from reference [28].

^dIdentification accuracy measures the ratio of number of colonies correctly identified with BARDOT as well as PCR and total number of colonies analyzed. Identification of colonies with BARDOT and mPCR were performed as a blind study.

^eOne colony (#R1-3/C1) analyzed with mPCR did not produce any amplified products, however, it was identified as O157 serovar after analysis with BARDOT library.