DIFFUSELY ADHERING ESCHERICHIA-COLI STRAINS INDUCE ATTACHING AND EFFACING PHENOTYPES AND SECRETE HOMOLOGS OF ESP PROTEINS

Recent epidemiological studies indicate that Escherichia coli strains which exhibit the diffuse adherence phenotype (DAEC strains) represent a potential cause of diarrhea in infants, We investigated the interac tion of DAEC strains isolated from diarrhea patients in Brazil and in Germany with epithelial cells in tissue culture, The investigated stra ins were identified as DAEC strains by (i) their attachment pattern, ( ii) presence of genes associated with the Dr family of adhesins, and ( iii) lack of genetic markers for other diarrhea-associated E. coli cat egories, Several clinical DAEC isolates were shown to secrete similar patterns of proteins into tissue culture medium, Protein secretion was found to be regulated by environmental parameters, namely, medium, te mperature, pH, and iron concentration, DAEC strains secreting these pr oteins induced accumulation of actin and tyrosine-phosphorylated prote ins at sites of bacterial attachment, leading to the formation of pede stals and/or extended surface structures, These changes were phenotypi cally similar to the attaching and effacing (A/E) lesions observed wit h enteropathogenic and some enterohemorrhagic E. coli strains carrying the locus of enterocyte effacement (LEE) pathogenicity island, Protei ns homologous to the EspA, EspB, and EspD proteins, necessary for sign al transduction events inducing AIE lesions, were identified by sequen ce analysis and cross-reaction of specific antibodies, However, initia lly nonadhering strains secreting these proteins induced signal transd uction events only after prolonged infection. These results indicate t hat secretion of the Esp proteins alone is not sufficient for efficien t signal transduction, This study further shows that some DAEC strains are likely to contain a homolog(s) of the LEE locus which may contrib ute to the pathogenic potential of DAEC.