TABLE 3.

Prevalence of puvA (ORF5) in K1 and non-K1 E. coli

Strains	Sourcea	% of isolates with ORF5 (no. tested)b	Pc
018:K1:H7	RS, DSMZ, or JJ	85.7 (28)
Other (non-O18) K1	WV or JJ	0.0 (38)	<0.0001
ECORd	HO	4.2 (72)	0.0001
ECOR-likee	JJ	0.0 (11)	<0.0001
ECORf	JJ	11.8 (17)

^aRS, Richard Silver, University of Rochester, Rochester, N.Y.; DSMZ, German Collection of Microorganisms and Cell Cultures, Braunschweig, Germany; JJ, James Johnson, University of Minnesota, Minneapolis,; WV, Willie Vann, Food and Drug Administration, Bethesda, Md.; HO, Howard Ochman, University of Arizona, Tucson.

^bDetected by PCR analysis with the puvA-specific primers given in Table 1. All O18:K1:H7 strains were also analyzed for ORF6 and ORF7 with the primers indicated in Table 1 and covaried with ORF5.

^cP values were determined by Fisher's exact test by comparison to the O18:K1:H7 strains; values of <0.01 were considered significant.

^dThe ECOR collection (14) is considered representative of the worldwide diversity of E. coli strains.

^e#51 (O25:K+) and #57 (O2:K5/7:H1), two of the three ORF5-positive strains from the ECOR collection (both from the B2 group), are similar to strains BOS 031 and BOS 080 and to strains V27, H19, V6, V24, and H1, respectively, which unlike #51 and #57 were negative for puvA. Strains more distantly related to #51 (BOS 70, BOS 100, BOS 77, and BOS 56) were also tested and found to be negative.

^fECOR strains #51 to #57, #59 to #66, #35, and #36. Strains #51 and #57 were kindly provided by an alternative source (James Johnson) and gave the same results as the equivalent strains obtained from Howard Ochman.