The possibility for identification of Salmonella enterica serotypes by sequence analysis of the 16S to 23S rRNA internal transcribed spacer was investigated by direct sequencing of polymerase chain reaction-amplified DNA from all operons simultaneously in a collection of 25 strains of 18 different serotypes of S. enterica, and by sequencing individual cloned operons from a single strain. It was only possible to determine the first 117 bases upstream from the 23S rRNA gene by direct sequencing because of variation between the rrn operons. Comparison of sequences from this region allowed separation of only 15 out of the 18 serotypes investigated and was not specific even at the subspecies level of S. enterica. To determine the differences between internal transcribed spacers in more detail, the individual rrn operons of strain JEO 197, serotype IV 43:z 4 ,z 2 3 :-, were cloned and sequenced. The strain contained four short internal transcribed spacer fragments of 382-384 bases in length, which were 98.4-99.7% similar to each other and three long fragments of 505 bases with 98.0-99.8% similarity. The study demonstrated a higher degree of interbacterial variation than intrabacterial variation between operons for serotypes of S. enterica.
Variation des sequences de la region 16S-23S ARNr d'espace intergenique chez Salmonella enterica.La possibilite d'identification des serotypes de S. enterica par analyse sequentielle des espaces intergeniques transcrits (ARNr de 16S a 23S) a ete etudiee grace a un sequencage direct de l'ADN, amplifie par PCR, de tous les operons d'une collection de 25 souches appartenant a 19 serotypes de S. enterica, et par un sequencage individuel des operons clones a partir d'une seule souche. Il est possible de determiner seulement les 117 premieres bases en amont du gene de ARNr 23S, par sequencage direct, car il y a des variations entre les operons rrn. La comparaison des sequences de cette region a permis de distinguer seulement 15 des 18 serotypes analyses et elle n'est pas specifique, meme au niveau des sous-especes de S. enterica. Pour determiner les differences plus detaillees entre les espaces intergeniques transcrits, les operons rrn individuels de la souche JEO 197 serotype IV 43:z 4 , z 2 3 :-, ont ete clones et sequences. Cette souche contient quatre fragments d'espaces intergeniques transcrits, de 382-384 bases et ayant 98,4 a 99,7<space>% de similarite entre eux, et trois fragments longs, de 505 bases et ayant 98,0 a 99,8<space>% de similarite. Ces resultats montrent que les variations entre bacteries sont plus grandes que les variations intrabacteriennes entre operons de serotypes divers de S. enterica. (C) 2000 Editions scientifiques et medicales Elsevier SAS