First isolation in Argentina of a highly virulent Shiga toxin-producing Escherichia coli O145:NM from a domestic cat

Hemolytic uremic syndrome (HUS) is distributed worldwide. In Argentina, more than 450 cases of HUS, mostly sporadic, are reported annually. The main serotype isolated is O157:H7, and among non-O157 STEC, O145:NM is the most frequent strain. We studied the relationship of companion animals living in contact with a child with sporadic HUS, as carriers of Shiga toxin-producing Escherichia coli (STEC) strains. Duplicate rectal swab samples were taken weekly from the household cat and dog at the home of a patient with HUS. Samples were plated on MacConkey and sorbitol MacConkey-CT agar. Confluent growth from each plate was screened for the presence of stx1, stx2 and rfbO157 gene by PCR assays. Up to 300 individual colonies taken from positive plates at screening were retested by PCR. The strain from the cat belonged to the highly virulent serotype O145:NM. Although this strain differed antigenically from the strain isolated from a child with HUS living in the same house, both carried the stx2, eae and ehxA virulence genes. The strain isolated from the dog belonged to the serotype O178:H19. An asymptomatic household cat may harbour the high virulent STEC strain, such as O145:NM, the second most frequently STEC serotype associated with HUS in Argentina. Companion animals are probably exposed to the same sources as the humans. More studies are needed to establish dogs and cats as sources of infection in the epidemiological cycle of infections caused by STEC strains, and to develop effective control strategies for this pathogen.