Search

Resume Enterobacter aerogenes est aujourd’hui, l’une des bacteries les plus frequemment impliquees dans les infections respiratoires et urinaires nosocomiales. Les souches isolees en clinique appartiennent a un meme clone et peuvent deployer plusieurs mecanismes de resistance aux β-lactamines. Les plus efficaces et les plus frequents sont une β-lactamase a spectre elargi (BLSE) de type TEM-24 et une cephalosporinase chromosomique dereprimee. Ces enzymes sont responsables de la resistance des souches a toutes les β-lactamines excepte l’imipeneme. Certaines souches ont la capacite, en plus des mecanismes de resistance precedemment decrits, de developper un phenotype de multiresistance (MDR), caracterise par la surexpression de systemes d’efflux actifs associes ou non a la perte des porines de la membrane externe. Ces 2 mecanismes sont regules par des systemes genetiques communs. L’operon marRAB et le gene ram sont actuellement les 2 systemes qui ont ete identifies chez E. aerogenes comme impliques dans la regulation de la MDR. Ainsi dote de tels mecanismes, E. aerogenes est capable de devenir resistant a l’ensemble des antibiotiques.

Two immunogenic proteins of 27 (CBF1) and 29 (CBF2) kDa from enteropathogenic Campylobacter species appear to bind to mammalian cells. We purified these two proteins from a pathogenic and adherent Campylobacter jejuni strain to homogeneity by using acid extraction, preparative gel electrophoresis, and electroelution. Polyclonal rabbit antisera to these proteins were prepared. Immunologic studies indicate that CBF1 corresponds to the PEB1 and CBF2 corresponds to the PEB4 described by Pei et al. (Z. Pei, R. T. Ellison, and M. Blaser, J. Biol. Chem. 226:16363-16369, 1991). Immunogold labeling of a C. jejuni adherent strain with anti-CBF1, anti-CBF2, and anti-PEB1 suggested that CBF1 (PEB1) is surface exposed while CBF2 (PEB4) is not. Analysis of whole-cell extracts from 14 strains by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis with 7 M urea and immunoblotting with antisera to CBF1 and CBF2 suggests that CBF proteins from adherent and nonadherent strains are different. Use of purified proteins in a microassay of adherence to cellular membranes indicated that CBF1 was much more adherent than CBF2. Adherence of C. jejuni to viable HeLa cells was markedly reduced with the antiserum to CBF1, whereas the CBF2 antiserum was a poor inhibitor. Purified CBF1 competitively inhibited adherence of whole bacteria to HeLa cells, whereas purified CBF2 was no better a competitor than bovine serum albumin. Adherence of CBF2 was markedly reduced in the presence of Tween 20 or SDS, whereas adherence of CBF1 was reduced only by SDS. We conclude that (i) CBF1 (PEB1) is surface exposed and may be the key protein for C. jejuni adhesion and (ii) CBF2 (PEB4) may be complexed with CBF1 and may passively coadhere with CBF1 under certain experimental conditions. Adherent and nonadherent strains contain different isotypes of these two proteins which could be useful markers of C. jejuni adhesion.

A new case of Schnitzler's syndrome is reported in a 72-year old man hospitalized for severe deterioration of his general condition associated with recurrent ancient urticaria. Paraclinical examinations, which showed inflammatory syndrome, bone condensation and IgM monoclonal gammapathy, led to the diagnosis of Schnitzler's syndrome, first described in 1972. Twenty-two cases have now been published, characterized by vasculitic urticaria, osteosclerosis and IgM macroglobulinaemia. There is also severe inflammatory syndrome and the other immunological examinations are normal. Recent studies suggest the possibility of uncontrolled activity of interleukin-1 alpha. The condition is chronic and usually benign, but the fear of malignant transformation in the long term makes the therapeutic choice difficult.

The subcellular localization of beta-lactamase produced by a secretion-cloning vector pIN-III was studied by immunolabelling of frozen thin sections of Escherichia coli. Using double immuno-gold detections and internal reference proteins, it is shown here that beta-lactamase encoded by this vector can be exported and that its overproduction leads to aggregation within the periplasm. This aggregation induces the appearance of electron-dense areas immunolabelled by the antiserum directed against the beta-lactamase at the external side of the cytoplasmic membrane. The overproduced enzyme is also secreted to the medium in vesicles budding from the outer membrane of lpp strains.

Evidence is presented that two circumferential zones of cell envelope differentiation, the periseptal annuli, exist in E. coli as previously observed in S. typhimurium. The periseptal annulus is located at the division site of cells. A strain overproducing a periplasmic protein, PhoS (phosphate-binding protein) has been used to provide a landmark for the periseptal compartment. The zone of adhesion does not involve inner-outer membrane fusion. This zone does not provide a strong physical barrier to protein diffusion in the periplasmic space, at least under conditions of plasmolysis.

A mutant strain devoid of the colicin A protease activity (cpr) located at the external face of the outer membrane has been isolated. The location of the mutation (about 74 min on the genetic map), its pleiotropic effects concerning mainly the protein composition of the outer membrane and sensitivity to phages and colicins, are very similar in cpr and in tpo, envZ, perA strains that are affected in the ompB locus. Conditions resulting in inhibition of the colicin A protease activity also result in transcriptional regulation of OmpF, OmpC, and LamB protein synthesis. The possibility for this protease as an osmosensor of the cell's external environment is discussed.

Colicins are released into the spent medium from colicinogenic cells. The pathway of release has been investigated in this study. The localization in producing cells of colicins A, E3 and of cloacin DF13 has been determined at various times after mitomycin C addition: no transient accumulation in the periplasmic space of colicinogenic E. coli K12 strains was detected by electron microscopy for any of the bacteriocins tested. Furthermore, asynchronous induction in individual cells was detected for each bacteriocin tested. These results strongly suggest that colicins, as well as cloacin DF13, do not transit through the periplasmic space before release from colicinogenic cells.

Precursor forms of periplasmic and outer membrane proteins were accumulated in phenethyl-alcohol-treated cells in membrane fractions. After removal of phenethyl alcohol, maturation occurred in the absence but not in the presence of carbonylcyanide m-chlorophenylhydrazone (30 microM). The site and kinetics of processing were investigated for OmpA, LamB and OmpF proteins and for maltose binding protein and TEM beta-lactamase. With regard to sites of processing, no fundamental difference between outer membrane and periplasmic proteins was observed. For maltose binding protein and TEM beta-lactamase, maturation, like that of outer membrane protein precursors, occurred in membrane fractions. Processing of pro-OmpA protein was about as fast as that of pro-LamB protein whereas pro-OmpF protein appeared to mature more slowly. While carbonylcyanide m-chlorophenylhydrazone (30 microM) prevented processing of all precursor forms, arsenate, which alters formation of ATP even when it was used at 1 mM, did not totally prevent maturation occurring. These results are discussed with regard to the biosynthesis and assembly of exported proteins.