Gene expression patterns of epithelial cells modulated by pathogenicity factors of Yersinia enterocolitica.

Epithelial cells express genes whose products signal the presence of pathogenic microorganisms to the immune system. Pathogenicity factors of enteric bacteria modulate host cell gene expression. Using microarray technology we have profiled epithelial cell gene expression upon interaction with Yersinia enterocolitica. Yersinia enterocolitica wild-type and isogenic mutant strains were used to identify host genes modulated by invasin protein (Inv), which is involved in enteroinvasion, and Yersinia outer protein P (YopP) which inhibits innate immune responses. Among 22 283 probesets (14,239 unique genes), we found 193 probesets (165 genes) to be regulated by Yersinia infection. The majority of these genes were induced by Inv, whose recognition leads to expression of NF-kappa B-regulated factors such as cytokines and adhesion molecules. Yersinia virulence plasmid (pYV)-encoded factors counter regulated Inv-induced gene expression. Thus, YopP repressed Inv-induced NF-kappa B regulated genes at 2 h post infection whereas other pYV-encoded factors repressed host cell genes at 4 and 8 h post infection. Chromosomally encoded factors of Yersinia, other than Inv, induced expression of genes known to be induced by TGF-beta receptor signalling. These genes were also repressed by pYV-encoded factors. Only a few host genes were exclusively induced by pYV-encoded factors. We hypothesize that some of these genes may contribute to pYV-mediated silencing of host cells. In conclusion, the data demonstrates that epithelial cells express a limited number of genes upon interaction with enteric Yersinia. Both Inv and YopP appear to modulate gene expression in order to subvert epithelial cell functions involved in innate immunity.

Fibronectin binding and cell surface hydrophobicity contribute to adherence properties of group B streptococci.

The matrix protein, fibronectin, which is detectable in various tissues, when present in the vaginal fluid of women in labour, indicates the rupture of membranes. It is known that many bacteria adhere to fibronectin, thus establishing a first step of infection. In women in labour, group B streptococci are common agents of chorioamnionitis. For group B streptococci, unspecific adherence mechanisms like negative net charge and hydrophobic interactions have already been discussed in literature. In the present study, group B streptococci isolates from 57 patients with premature rupture of membranes were studied for fibronectin binding activities, using a particle agglutination assay and for cell surface hydrophobicity, by testing adhesion to hydrocarbons. Particle agglutination assays and adhesion assays were done with strains grown on blood-containing media and media without blood. Fibronectin binding was shown to be present in 14 and 11 out of 57 isolates grown on Mueller-Hinton and Tryptic Soy agar, respectively. When the strains were grown on blood-containing media, fibronectin-binding was found to be concomitant with decreased hydrophobicity. According to the results obtained in a total of 57 strains, cell surface hydrophobicity is an unspecific adhesion factor in group B streptococci. Fibronectin binding seems to be an additional adherence factor in some of the strains and may be assumed to play a major role in establishing infectious processes.

Bacteroides fragilis adheres to laminin significantly stronger than Bacteroides thetaiotaomicron and other species of the genus.

The laminin binding properties of eight species of the genus Bacteroides were examined using latex particle agglutination assay. B. fragilis was found to bind strongly to laminin, whereas all other species tested showed no or only weak laminin adherence. The pronounced differences in laminin binding activity between B. fragilis on the one side and B. thetaiotaomicron and B. ovatus on the other were determined to be statistically significant (p < 0.001 and p < 0.01, respectively). With regard to the relevance of laminin adherence for bacterial pathogenicity and invasiveness, our results give a possible explanation for the well-known finding that B. fragilis is the most frequently isolated pathogen in anaerobic bacteremia.

Microbial flora of sinus tracts and root canals of non-vital teeth.

The occurrence of bacteria in 12 endodontically induced periodontal lesions associated with sinus tracts was examined. The microbial flora encountered in the sinus tract was compared with that of the root canal of the involved teeth which had not experienced any prior endodontic therapy. All microbiological samples taken from the sinus tract and from the root canal system contained bacteria. Seventy-one strains were detected in the extraradicular lesions. Of the anaerobic species, Fusobacterium nucleatum (7 strains), Prevotella intemedia (4 strains) and P. oralis (4 strains) were most frequently found. In the group of the facultative anaerobes Streptococcus spp. were predominant. Ninety-four strains were isolated from the root canal system of the 12 teeth. P. intermedia (6 strains), P. buccae (5 strains), F. nucleatum (5 strains) and Lactobacillus plantarum (5 strains) were most common. In 9 cases, species present in the root canal could be revealed in the extraradicular lesions. It was concluded that a variety of microorganisms were capable of colonizing endodontically induced, extraradicular lesions clinically characterized by sinus tracts.

Fibronectin and vitronectin binding of Bacteroides fragilis and eight other species of the genus.

The fibronectin and vitronectin bindings of 152 strains belonging in 9 Bacteroides species of different origins were tested by means of latex agglutination. 23% of the strains isolated from faeces exhibited fibronectin binding, as did 46% of the strains obtained from severe infections. Most of the strains displaying fibronectin binding belonged to the species Bacteroides fragilis or Bacteroides vulgatus. The binding could be inhibited by preincubation of the cells with an excess amount of fibronectin. Vitronectin binding was less common, but was always observed in parallel with fibronectin binding.

In vitro activity of meropenem compared with imipenem, metronidazole, ampicillin, and ampicillin/sulbactam against anaerobes.

The aim of the present study was to compare the in vitro activity of meropenem (ICI 194660, CAS 96036-03-2) with imipenem, metronidazole, clindamycin, ampicillin and ampicillin/sulbactam against a variety of anaerobic bacteria using an agar dilution method. 423 clinical isolates were tested belonging to 70 species of 15 anaerobic genera. They included Bacteroides fragilis (n = 62), Bacteroides thetaiotaomicron (n = 45), Prevotella bivia (n = 11), Fusobacterium nucleatum (n = 12), Clostridium perfringens (n = 15) and several rarely isolated species and genera, e.g. Selenomonas sputigena and Clostridium symbiosum. Bacteroides species were inhibited by meropenem at < or = 2.0 micrograms/ml, Clostridium species, including C. difficile, at < or = 4.0 micrograms/ml and all the other anaerobes at < or = 0.5 microgram/ml. Meropenem and imipenem were the most active substances, but often equal to, or only slightly better than, metronidazole, clindamycin or ampicillin/sulbactam, dependent on species. Meropenem was especially active against Bacteroides gracilis (MIC90 0.015 microgram/ml), Prevotella disiens (MIC90 0.03 microgram/ml), Fusobacterium nucleatum (MIC90 0.015 microgram/ml), Clostridium perfringens (MIC90 0.015 microgram/ml) and Veillonella parvula (MIC90 0.03 microgram/ml). The results obtained indicate that meropenem might be a useful adjunct to chemotherapy of anaerobic and mixed aerobic and anaerobic infections.

Comparison of the Cobas-Bact five-hour susceptibility testing system with the NCCLS agar diffusion and dilution methods.

The results of susceptibility tests performed by the Cobas-Bact system were compared with those of the NCCLS agar diffusion (Kirby-Bauer) and NCCLS agar dilution methods. A total of 998 clinical isolates were tested against 10 to 18 antimicrobial agents. Essential agreement (comprising full agreement and minor discrepancies) varied from 90.5% to 99.2% on comparison of Cobas-Bact with Kirby-Bauer results, depending on the bacterial group (mean for all 998 strains tested 95.7%). These figures ranged from 91% to 99.2% (mean 96.3%) for the Cobas-Bact/MIC comparison and from 95.2% to 99.7% (mean 98.7%) for the Kirby-Bauer/MIC comparison. The best results were found for Enterobacteriaceae and Staphylococcus aureus, whereas for enterococci and coagulase-negative staphylococci there was a lower rate of essential agreement in all three comparisons. In the case of Pseudomonas aeruginosa there was a good rate of essential agreement but many minor discrepancies, resulting in a disappointing rate of full agreement of between 67.5% and 78.9% in the three comparisons. The Cobas-Bact system would appear to provide satisfactory susceptibility test results in most cases, however there are still some major problems in the system which should be resolved.