FIG. 1.

A lifA mutant of EPEC retains the ability to perform localized adherence and attaching and effacing activities. By allelic exchange, the wild-type lifA locus of EPEC strain E2348/69 was replaced with an allele that contains an 1,890-bp deletion, at which site a nonpolar kanamycin resistance cassette was inserted, to create the lifA mutant strain UMD704. (A) Agarose gel electrophoresis of the products of a PCR targeting a portion of the lifA gene. The product from mutant strain UMD704 is approximately 1,130-bp smaller than that from the wild-type strain E2348/69, confirming the replacement of the 1,980-bp fragment with the 850-bp aphA-3 gene cassette. The sizes (in kilobase pairs) of molecular standards are indicated on the left. (B) Phase-contrast micrograph (top) and corresponding fluorescein isothiocyanate-phalloidin fluorescence micrograph (bottom) of HEp-2 cells infected the lifA mutant UMD704. Arrows show microcolonies of bacteria associated with accumulations of filamentous actin that are characteristic of the localized adherence and attaching and effacing phenotypes.