Weiss-Muszkat, M., Food-Safety Research Unit, Department of Food Science, Volcani Center, P.O. Box 6, Beth-Dagan 50250, Israel
Shakh, D., Food-Safety Research Unit, Department of Food Science, Volcani Center, P.O. Box 6, Beth-Dagan 50250, Israel
Zhou, Y., Department of Molecular, Cellular and Developmental Biology, University of Michigan, Ann Arbor, MI 48109, United States
Pinto, R., Food-Safety Research Unit, Department of Food Science, Volcani Center, P.O. Box 6, Beth-Dagan 50250, Israel
Belausov, E., Confocal Microscopy Unit, ARO, Volcani Center, Beth-Dagan, Israel
Chapman, M.R., Department of Molecular, Cellular and Developmental Biology, University of Michigan, Ann Arbor, MI 48109, United States
Sela, S., Food-Safety Research Unit, Department of Food Science, Volcani Center, P.O. Box 6, Beth-Dagan 50250, Israel

Enteropathogenic Escherichia coli (EPEC) is an important causal agent of diarrheal illness throughout the world. Nevertheless, researchers have only recently begun to explore its capacity to form biofilms. Strain 055:H7 (DMS9) is a clinical isolate belonging to the atypical EPEC (aEPEC) group, which displays a high degree of genetic relatedness to enterohemorrhagic E. coli. Strain DMS9 formed a robust biofilm on an abiotic surface at 26°C, but not at 37°C. It also formed a dense pellicle at the air-liquid interface and developed a red, rough, and dry (RDAR) morphotype on Congo red agar. Unlike a previously described E. coli O157:H7 strain, the aEPEC strain seems to express cellulose. Transposon mutagenesis was used to identify biofilm-deficient mutants. One of the mutants was inactivated in the csgFG genes, required for assembly and secretion of curli fimbriae, while a second mutant had a mutation in cri, a thermosensitive global regulator that modulates σs activity and downstream expression of curli and cellulose. The two mutants were deficient in their biofilm formation capabilities and did not form a pellicle at the air-liquid interface. Unlike in Salmonella, the csgFG mutant in aEPEC completely lost the RDAR phenotype, while the crl mutant displayed a unique RDAR "pizza"-like morphotype. Genetic complementation of the two mutants resulted in restoration of the wild-type phenotype. This report is the first to describe and analyze a multicellular behavior in aEPEC and support a major role for curli and the crl regulator in biofilm development at low temperatures corresponding to the nonmammalian host environment. Copyright © 2010, American Society for Microbiology. All Rights Reserved.