Characterisation of Listeria ivanovii isolates from the UK using pulsed-field gel electrophoresis

Forty-three Listeria ivanovii isolates were collected in the UK between 1991 and 1997 from: 35 animal infections; two human infections; five foods; and one environmental source. A further two type strains of L. ivanovii (subsp. ivanovii and subsp. londoniensis) were obtained from a culture collection. These bacteria were characterised by conventional phenotypic methods and by pulsed-field gel electrophoresis (PFGE) using ApaI and SmaI. Forty-two of the isolates from the UK were identified as L. ivanovii subsp. ivanovii and the remaining culture as L. ivanovii subsp. londoniensis. Six and four PFGE profiles were obtained using ApaI and SmaI digestion respectively; six composite profiles were obtained combining the results for both enzymes. The PFGE profile of the UK L. ivanovii subsp. londoniensis (isolated from processed shrimps) was similar to the type strain of this subspecies and differed from all of the L. ivanovii subsp. ivanovii tested. The majority of isolates (38 out of 45) belonged to one profile showing that the UK population of this bacterium is much less genetically diverse than similar studies have shown for Listeria monocytogenes.