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Aims: Yersinia enterocolitica causes several syndromes in humans. The most common presentation is enterocolitis in children, presenting as fever and diarrhoea. A Y. enterocolitica multiple strain infection in twin infants was investigated. Methods and Results: One isolate was recovered from one patient and two morphologicallydifferent isolates were recovered from the other infant. Biochemically, all isolates were identi®ed as Y. enterocolitica group. The genomic DNA from each strain was puri®ed and DNA ®ngerprinting was performed. The banding patterns observed for Y. enterocolitica isolates 2 and 3, from patients 1 and 2, respectively, were identical when comparing the presence or absence of major bands. However, Y. enterocolitica isolate 1, from patient 1, showed a distinctive banding pattern from isolates 2 and 3. Conclusions: The ®ndings indicate that one infant was colonized by more than one strain of Y. enterocolitica, demonstrating that multiple strains can colonize and invade a patient. Signi®cance and Impact of the Study: Recognition of multiple strain infections can be important in diagnosis, treatment and prognosis of Y. enterocolitica infections, as well as in disease epidemiology. The technique described here offers a straightforward method for strain comparison.

Inorganic polyphosphate (polyP) and its metabolic enzymes are important in several cellular processes related with virulence and antibiotic susceptibility. Accordingly, bacterial polyP synthesis has been proposed as a good target for designing novel antivirulence molecules as alternative to conventional antibiotics. In most pathogenic bacteria, polyphosphate kinase 1 (PPK1), in charge of polyP synthesis from ATP, is widely conserved. Current colorimetric and radioactive polyP synthesis enzymatic assays are not suitable for high-throughput screening of PPK1 inhibitors. Given the ability of polyP to modify the excitation-emission spectra of DAPI (4ʹ-6-diamidino-2-phenylindole), a fluorescence assay was previously developed by using a purified recombinant PPK1 enzyme from Escherichia coli . In this work we have developed a suitable methodology for high-throughput measurement of E. coli PPK1 activity. This platform can be used for the screening putative antimicrobial molecules for related enteropathogenic bacteria.