Tilivalline- and Tilimycin-Independent Effects of Klebsiella oxytoca on Tight Junction-Mediated Intestinal Barrier Impairment

Klebsiella oxytoca causes antibiotic-associated hemorrhagic colitis and diarrhea. This was attributed largely to its secreted cytotoxins tilivalline and tilimycin, inductors of epithelial apoptosis. To study whether Klebsiella oxytoca exerts further barrier effects, T84 monolayers were challenged with bacterial supernatants derived from tilivalline/tilimycin-producing AHC6 or its isogeneic tilivalline/tilimycin-deficient strain Mut-89. Both preparations decreased transepithelial resistance, enhanced fluorescein and FITC-dextran-4kDa permeabilities, and reduced expression of barrier-forming tight junction proteins claudin-5 and -8. Laser scanning microscopy indicated redistribution of both claudins off the tight junction region in T84 monolayers as well as in colon crypts of mice infected with AHC6 or Mut-89, indicating that these effects are tilivalline/tilimycin-independent. Furthermore, claudin-1 was affected, but only in a tilivalline/tilimycin-dependent manner. In conclusion, Klebsiella oxytoca induced intestinal barrier impairment by two mechanisms: the tilivalline/tilimycin-dependent one, acting by increasing cellular apoptosis and a tilivalline/tilimycin-independent one, acting by weakening the paracellular pathway through the tight junction proteins claudin-5 and -8.

1H, 13C, 15N resonance assignment of the C-terminal domain of the bifunctional enzyme TraI of plasmid R1

Transfer of genetic material is the main mechanism underlying the spread of antibiotic resistance and virulence factors within the bacterial community. Conjugation is one such process by which the genetic material is shared from one bacterium to another. The DNA substrate is processed and prepared for transfer by a multi-protein complex called the relaxosome .The relaxosome of plasmid R1 possesses the most crucial enzyme TraI which, both nicks and unwinds the dsDNA substrate. TraI comprises 1765 residues and multiple functional domains, including those catalyzing the DNA trans-esterase (relaxase) on the dsDNA designated for a conjugative transfer and DNA helicase activities. Structural and functional studies have been reported for most of the TraI except the C-terminal domain spanning from residue 1630 to 1765. This region is the least understood part of TraI and is thought to be highly disordered and flexible. This region, being intrinsically disordered, is hypothesized to be serving as an interacting platform for other proteins involved in this DNA transfer initiation mechanism. In this work, we report the ¹H, ¹³C, ¹⁵N resonance assignment of this region as well as the secondary structure information based on the backbone chemical shifts.

Causes of hematochezia and hemorrhagic antibiotic-associated colitis in children and adolescents

Diseases causing hematochezia range from benign to potentially life-threatening. Systematic pediatric data on the causes of hematochezia are scarce. We studied the underlying causes and long-term outcome of hematochezia in children. We further investigated the relevance of antibiotic-associated hemorrhagic colitis in children, especially if caused by Klebsiella oxytoca.Infants, children, and adolescents with hematochezia were recruited prospectively. Patients were grouped according to age (<1 year, 1-5 years, 6-13 years, >14 years). In addition to routine diagnostics, K oxytoca stool culture and toxin analysis was performed. We collected data on history, laboratory findings, microbiological diagnostic, imaging, final diagnosis, and long-term outcome.We included 221 patients (female 46%; age 0-19 years). In 98 (44%), hematochezia was caused by infectious diseases. Endoscopy was performed in 30 patients (13.6%). No patient died due to the underlying cause of hematochezia. The most common diagnoses according to age were food protein-induced proctocolitis in infants, bacterial colitis in young children, and inflammatory bowel disease in children and adolescents. Seventeen (7.7%) had a positive stool culture for K oxytoca. Antibiotic-associated colitis was diagnosed in 12 (5%) patients: 2 caused by K oxytoca and 2 by Clostridium difficile; in the remaining 8 patients, no known pathobiont was identified.Infections were the most common cause of hematochezia in this study. In most patients, invasive diagnostic procedures were not necessary. Antibiotic-associated hemorrhagic colitis caused by K oxytoca was an uncommon diagnosis in our cohort. Antibiotic-associated colitis with hematochezia might be caused by pathobionts other than C difficile or K oxytoca.

The Toxin-Producing Pathobiont Klebsiella oxytoca Is Not Associated with Flares of Inflammatory Bowel Diseases

BACKGROUND

Alterations in the intestinal microbiota are thought to be involved in the pathogenesis of inflammatory bowel diseases (IBD). Klebsiella oxytoca is an intestinal pathobiont that can produce a cytotoxin (tillivaline).

AIM

We aimed to elucidate the pathogenetic relevance of toxin-producing K. oxytoca in patients with IBD flares and investigated the clonal relationship of K. oxytoca isolates from IBD patients using multilocus sequence typing (MLST).

METHODS

Fecal samples of 235 adult IBD patients were collected from January 2008 to May 2009 and were tested for K. oxytoca, C. difficile toxin, and other pathogens by standard microbiological methods. Clinical data and disease activity scores were collected. K. oxytoca isolates were tested for toxin production using cell culture assays. A total of 45 K. oxytoca isolates from IBD patients, healthy, asymptomatic carriers and from patients with antibiotic-associated hemorrhagic colitis in part from our strain collection were tested for their clonal relationship using MLST.

RESULTS

The prevalence of K. oxytoca in IBD overall was 4.7%. Eleven K. oxytoca isolates were detected. Two of 11 isolates were tested positive for toxin production. There was no significant difference in the distribution of K. oxytoca isolates between the groups (active vs. remission in UC and CD). MLST yielded 33 sequence types. K. oxytoca isolates from IBD did not cluster separately from isolates from asymptomatic carriers.

CONCLUSIONS

Our data demonstrate that toxin (tilivalline)-producing K. oxytoca is not associated with IBD flares.

Antibiotic-associated hemorrhagic colitis caused by cytotoxin-producing Klebsiella oxytoca

Klebsiella oxytoca was recently described as the causative organism for antibiotic-associated hemorrhagic colitis (AAHC). It is currently not known if this novel gastrointestinal infection exists in children. AAHC is usually preceded by antibiotic treatment with penicillins, which are frequently prescribed for pediatric patients. In contrast to colitis caused by Clostridium difficile, colitis caused by K oxytoca is usually segmental and located predominantly in the right colon. Patients with AAHC typically present with abdominal pain and almost always bloody diarrhea. We present here the case of an adolescent patient who developed acute abdominal pain and bloody diarrhea after antibiotic treatment for acute urinary infection with amoxicillin-clavulanate. Right-sided colitis was verified by abdominal sonography. Stool culture tested negative for common gastrointestinal pathogens but yielded K oxytoca. Toxin production of the isolated strain was verified in a cell-culture assay. Cessation of the causative antibiotic treatment led to rapid improvement and cessation of bloody diarrhea within 3 days. We report here the first (to our knowledge) pediatric case of K oxytoca infection causing AAHC. Establishing the diagnosis of AAHC by culturing K oxytoca and demonstrating right-sided colitis with noninvasive imaging studies might prevent unnecessary invasive procedures in children with bloody diarrhea.

Variable-density flow in heterogeneous porous media--laboratory experiments and numerical simulations

Konz, M., Ackerer, P., Younes, A., Huggenberger, P., Zechner, E., 2009a. 2D Stable Layered Laboratory-scale Experiments for Testing Density-coupled Flow Models. Water Resources Research, 45. doi:10.1029/2008WR007118., a series of laboratory-scale 2D tank experiments were conducted and accurately simulated for density driven flow problems on homogeneous porous media. In the present work, we extended the numerical and experimental studies to heterogeneous problems. The heterogeneous porous medium was constructed with a low permeability zone in the centre of the tank and had well-defined parameters and boundary conditions. Concentration distributions were measured in high resolution using a photometric method and an image analysis technique. The numerical model used for the simulations was based on efficient advanced approximations for both spatial and temporal discretizations. The Method Of Lines (MOL) was used to allow higher-order temporal discretization. Three different boundary conditions, corresponding to different localizations of the inflow and the outflow openings at the opposite edges of the tank, were applied to investigate different flow scenarios in the heterogeneous porous medium flow tank. Simulation results of all three density coupled experiments revealed a density-dependent behavior of dispersion. Thus, a reduction of dispersivites was required to obtain a good matching of the experimental data. The high quality of the experiments enabled a detailed testing of numerical variable-density flow codes under heterogeneous conditions. Therefore, the experiments were considered to be reliable benchmark tests.