Silencing and reactivation of urease in Yersinia pestis is determined by one G residue at a specific position in the ureD gene.

Yersinia pestis, the plague agent, is a naturally nonureolytic microorganism, while all other Yersinia species display a potent urease activity. In this report we demonstrate that Y. pestis harbors a complete urease locus composed of three structural (ureABC) and four accessory (ureEFGD) genes. Absence of ureolytic activity is due to the presence of one additional G residue in a poly(G) stretch, which introduces a premature stop codon in ureD. The presence of the same additional G in eight other Y. pestis isolates indicates that this mutation is species specific. Spontaneous excision of the extra G occurs at a frequency of 10(-4) to 10(-5) and restores a ureolytic phenotype to Y. pestis. The virulence of two independent ureolytic clones of Y. pestis injected either intravenously, subcutaneously, or intragastrically did not differ from that of the parental strain in the mouse infection model. Coinfection experiments with an equal number of ureolytic and nonureolytic bacteria did not evidence any difference in the ability of the two variants to multiply in vivo and to cause a lethal infection. Altogether our results demonstrate that variation of one extra G residue in ureD determines the ureolytic activity of Y. pestis but does not affect its virulence for mice or its ability to multiply and disseminate.

Molecular identification of Pasteurella dagmatis peritonitis in a patient undergoing peritoneal dialysis.

Pasteurella dagmatis was identified as the etiologic agent of peritonitis in a continuous ambulatory peritoneal dialysis patient by utilizing a molecular kit in our hospital's clinical laboratory. This method would appear a useful approach to identify a species of Pasteurella not included in the existing database of commercial identification kits when discrepancies exist between phenotypic tests.

Characterization of IS1541-like elements in Yersinia enterocolitica and Yersinia pseudotuberculosis.

We characterized Yersinia enterocolitica and Yersinia pseudotuberculosis insertion sequences related to insertion sequence 1541, recently identified in Yersinia pestis. For each of the two species, two insertion sequence copies were cloned and sequenced. Genetic elements from Y. pseudotuberculosis were almost identical to insertion sequence 1541, whereas these from Y. enterocolitica were less related. Phylogenetic analysis of the putative transposases encoded by insertion sequences from the three pathogenic members of the genus Yersinia showed that they clustered with those encoded by Escherichia coli and Salmonella enterica elements belonging to the insertion sequence 200/insertion sequence 605 group. Insertion sequences originating from Y. pestis and Y. pseudotuberculosis constitute a monophyletic lineage distinct from that of Y. enterocolitica.

Molecular characterization of IS1541 insertions in the genome of Yersinia pestis.

The genome of Yersinia pestis, the causative agent of plague, contains at least 30 copies of an element, designated IS1541, which is structurally related to IS200 (85% identity). One such element is inserted within the chromosomal inv gene (M. Simonet, B. Riot, N. Fortineau, and P. Berche, Infect. Immun. 64:375-379, 1996). We characterized other IS1541 insertions by cloning 14 different Y. pestis 6/69M loci carrying a single copy of this insertion sequence (IS) into Escherichia coli and, for each element, sequencing 250 bp of both flanking regions. In no case was this IS element inserted into large open reading frames; however, in eight cases, it was detected downstream (17 to 139 bp) of genes thought to be transcribed monocistronically or which constituted the last gene of an operon, and in only one case was it detected upstream (37 bp) of the first gene of an operon. Sequence analysis revealed stem-loop structures (deltaG, < -10 kcal) resembling rho-independent transcription terminators in 8 of the 14 insertion sites. These motifs might constitute hot spots for insertion of this IS1541 element within the Y. pestis genome.

[In vitro study of antibacterial activity of cefepime (Axepim) against gram negative bacteria: comparison with cephalosporins and other beta-lactams]. / Etude in vitro de l'activité antibactérienne du céfépime (axepim) sur les bacilles à gram négatif: comparaison avec les céphalosporines et les autres beta-lactamines.

The susceptibility to cefepime and to other beta-lactams of 1017 inducible cephalosporinase-producing enterobacteria, 897 Pseudomonas aeruginosa strains, and 295 Acinetobacter baumanii strains was studied over a two-year period (July 1, 1993 to June 30, 1995). The isolates were from patients in visceral surgery, intensive care, and clinical hematology wards. Cefepime was compared to other third-generation cephalosporins and to imipenem, aztreonam, and the piperacillin-tazobactam combination. Cefepime was more active than the other cephalosporins against Enterobacter cloacae, Serratia marcescens and Citrobacter freundii. Activity of cefepime on the study isolates was also greater than that of aztreonam and of the piperacillin-tazobactam combination. Cefepime exhibited outstanding activity against Pseudomonas aeruginosa strains except those with the O12 serotype.