Beyond serotypes and virulence-associated factors: Detection of genetic diversity among O153 : H45 CFA/I heat-stable enterotoxigenic Escherichia colistrains

Characterization of enterotoxigenic Escherichia coli (ETEC) has been based almost exclusively on the detection of phenotypic traits such as serotypes and virulence-associated factors: heat-labile (LT) and heat-stable (ST) tox ins and colonization factors (CFs). In the present work we show that the an alysis of band patterns generated by randomly amplified polymorphic DNA (RA PD) analysis and pulsed-field gel electrophoresis (PFGE) of digested chromo somal DNA can be used to detect genetic diversity among ETEC strains expres sing identical phenotypic traits. The study included 29 ETEC isolates from Latin America and Spain expressing the phenotype O153:H45 CFA/I ST plus 1 r ough derivative, 2 nonmotile derivatives, and 1 O78:H12 CFA/I ST isolate, a nd a representative of a genetically distinct ETEC group. The results showe d that the O153:H45 CFA/I ST ETEC isolates belong to a single clonal cluste r whose isolates share on average, 84% of the RAPD bands and 77% of the PFG E restriction fragments, while the O78:H12 isolate shared only 44 and 4% of the RAPD bands and PFGE fragments, respectively, with the isolates of the O153:H45 group. More relevantly, RAPD and PFGE fingerprints disclosed the p resence of different clonal lineages among the isolates of the O153:H45 clu ster. Some of the genetic variants were isolated from defined geographic ar eas, while places like Sao Paulo City in Brazil and the middle-eastern part of Argentina were populated by several genetic variants of related, but no t identical, ETEC strains. These results show that molecular biology-based typing methods can disclose strain diversity, which is usually missed in st udies restricted to phenotypic typing of ETEC.