Overdiagnosis of essential tremor

Abstract

2but it did not carry the large invasivity plasmid and was rough for its O-antigen. No Shiga toxin producing Ec o l i w e r e detected in the patient’s stool but the S sonnei isolate (named CB7888) showed toxicity to cultured Vero cells and was positive for Stx or Stx1 but negative for Stx2 in a latex agglutination assay (VTEC-RPLA). PCR amplification with primers KS7 and KS8 showed an stx or an s t x1 gene in this s t r a i n . 3 The nucleotide sequence of the entire s t x-gene present in CB7888 was determined (EMBL database, accession AJ132761). The DNA-sequence of the s t xA subunit was found to be completely identical to the sequence of the s t xA subunit found in S dysenteriae type 1 (accession M19437), whereas a one nucleotide difference was found between the coding regions for the s t xB subunit that does not alter the aminoacid residue. 4 An s t x-transducing bacteriophage was isolated from strain CB7888 after mitomycin C induction. The s t x-gene could be transduced by the bacteriophage to s t xnegative reference strains of S sonnei and to a toxin-negative E coli K-12 strain that became lysogenic for the bacteriophage. The lysogenic recipients became positive for production of verocytotoxin and the presence of the s t x-gene in the recipients was shown by PCR. In Shiga-toxin-producing E coli strains, the genes for production of s t x1 and s t x2 are commonly encoded by bacteriophages whereas the s t x-gene of S dysenteriae type 1 is chromosomally located. 5 Production of Stx was only reported for S dysenteriae type 1 5 and to our knowledge this is the first time that a functional s t x-gene was detected in S sonnei. In contrast to S dysenteriae type 1, the s t x-gene of S sonnei w a s found to be encoded by a bacteriophage that is able to transduce the gene to other strains of S sonnei and to E coli K 12. It seems likely that s t x-gene of strain CB7888 originates from S dysenteriae type 1 because the DNA sequences of the two coding regions of the s t xA subunit are identical and differ in three nucleotides from the s t x1A subunit of E coli. It appears thus possible that a transducing Shigella-bacteriophage has mobilised the s t x-gene of S dysenteriae type 1, which has now spread to S sonnei and possibly to other enterobacterial s p e c i e s .