Classification of Ralstonia pickettii biovar 3/'thomasii' strains (Pickett1994) and of new isolates related to nosocomial recurrent meningitis as Ralstonia mannitolytica sp nov.

Strains isolated independently from two patients could be recognized as Ral stonia pickettii biovar 3/' thomasii'. The 16S rDNA sequences of these stra ins and two other strains of R, pickettii biovar 3/' thomasii' clustered at less than 98% similarity versus all other described Ralstonia species and at less than 97% versus the two other R, pickettii biovars. The separate sp ecies status of R. pickettii biovar 3/' thomasii' was confirmed by DNA-DNA hybridization, indicating less than 60% DNA homology with the R, pickettii biovars Va-1 and Indicating less than 60% DNA homology with the R, picketti i biovars Va-1 Va-2 and with two as-yet unclassified but biochemically simi lar Ralstonia strains. Phenotypically, this Ralstonia species can be distin guished from all described Ralstonia species by its acidification of D-arab itol and mannitol and by its lack of nitrate reduction and of alkalinizatio n of tartrate and from two as-yet unclassified Ralstonia strains only by it s lack of nitrate reduction. The name Ralstonia mannitolytica sp, nov. is p roposed, reflecting the characteristic acidification of mannitol, Resistanc e to desferrioxamine is another difference from R, pickettii and Ralstonia solanacearum. Although several nosocomial outbreaks have been associated wi th R, mannitolytica, life-threatening infections have not yet been reported , possibly due to misidentification as Pseudomonas fluorescens or Burkholde ria cepacia, In at least one of the two cases reported here, the R, mannito lytica isolate was found to be clinically relevant, causing recurrent nosoc omial meningitis, with an infected implanted catheter as the source. The ty pe strain of R, mannitolytica is NCIMB 10805(T) (= LMG 6866T), which was is olated during the first described outbreak as 'Pseudomonas thomasii' at St Thomas' Hospital, London, UK, in 1971.