Resistance to beta-lactam antibiotics in Aeromonas hydrophila isolated from rainbow trout (Oncorhynchus mykiss). (57/265)

Bacterial infections caused by members of the genus Aeromonas, with a relatively high antibiotic resistance, are among the most common and troublesome diseases of fish raised in ponds with recirculation systems. In this study, carried out at an experimental aquaculture station in northern Portugal, 51 strains identified as belonging to the genus Aeromonas were isolated from 20 rainbow trout (Oncorhynchus mykiss) skin and kidney samples, as well as from raceway water samples. Macro- and microscopic examination of the fish tissues revealed lesions or cellular alterations in skin and kidney that seemed to correlate with the presence of those isolates. The sensitivity of all isolated strains to different groups of beta-lactam antibiotics (penicillins, cephalosporins, monobactams and carbapenems) was evaluated using the disc diffusion method. The highest rates of resistance were to amoxicillin, carbenicillin and ticarcillin. Unexpected resistance to imipenem, an antibiotic of clinical usage, was also detected, which suggests that resistance may have been transferred to the Aeromonas population from the environment.  (+info)

Complete type III secretion system of a mesophilic Aeromonas hydrophila strain. (58/265)

We have investigated the existence and genetic organization of a functional type III secretion system (TTSS) in a mesophilic Aeromonas strain by initially using the Aeromonas hydrophila strain AH-3. We report for the first time the complete TTSS DNA sequence of an Aeromonas strain that comprises 35 genes organized in a similar disposition as that in Pseudomonas aeruginosa. Using several gene probes, we also determined the presence of a TTSS in clinical or environmental strains of different Aeromonas species: A. hydrophila, A. veronii, and A. caviae. By using one of the TTSS genes (ascV), we were able to obtain a defined insertion mutant in strain AH-3 (AH-3AscV), which showed reduced toxicity and virulence in comparison with the wild-type strain. Complementation of the mutant strain with a plasmid vector carrying ascV was fully able to restore the wild-type toxicity and virulence.  (+info)

Enterotoxicity of clinical and environmental isolates of Aeromonas spp. (59/265)

Of 147 isolates of three species of Aeromonas, 54 were from clinical and 93 from environmental sources. When tested for enterotoxin production, most of the isolates (56%) caused accumulation of fluid in rabbit ileal loops (RILs). Although large proportions of clinical and environmental isolates of A. caviae (55% and 65%, respectively) elicited such a response in RILs, isolates of A. hydrophila and A. sobria produced significantly more fluid (p less than 0.05). Furthermore, the environmental strains of A. hydrophila and A. sobria produced more fluid than the clinical isolates (p less than 0.05). The strains of Aeromonas spp. that caused little or no fluid accumulation in the initial experiments became enterotoxin producers after 1-3 passages through RILs, regardless of their source, and showed gradual enhancement of fluid outpouring after each passage. The present study suggests that all strains of these species of Aeromonas are potentially enterotoxigenic, whether from clinical or environmental sources.  (+info)

Fatal aeromonas hydrophila infection of soft tissue after endoscopic injection sclerotherapy for gastric variceal bleeding. (60/265)

Aeromonas hydrophila, an anaerobic gram-negative bacillus, can cause severe infections in immune-compromised patients. We present a 45-year-old cirrhotic man who suffered from hematemesis and received emergency endoscopic injection sclerotherapy (EIS) for gastric variceal bleeding. Twenty-one hours after EIS, painful swelling of the bilateral lower extremities and fever occurred. Severe soft-tissue infections with emergence of hemorrhagic bullae over the bilateral lower extremities followed. Even under aggressive treatment, the patient died of overwhelming sepsis 42 hours after EIS. Cultures of the blood and serosanguineous fluid from the hemorrhagic bullae revealed Aeromonas hydrophila. To the best of our knowledge, this is the first case of fatal Aeromonas hydrophila infection after emergancy EIS for gastric variceal bleeding reported in the English literature. It is worth emphasizing that physicians should consider Aeromonas hydrophila infection in cirrhotic patients who develop soft-tissue infections after variceal bleeding whether emergency EIS has been performed or not.  (+info)

Structural analysis of the Laetiporus sulphureus hemolytic pore-forming lectin in complex with sugars. (61/265)

LSL is a lectin produced by the parasitic mushroom Laetiporus sulphureus, which exhibits hemolytic and hemagglutinating activities. Here, we report the crystal structure of LSL refined to 2.6-A resolution determined by the single isomorphous replacement method with the anomalous scatter (SIRAS) signal of a platinum derivative. The structure reveals that LSL is hexameric, which was also shown by analytical ultracentrifugation. The monomeric protein (35 kDa) consists of two distinct modules: an N-terminal lectin module and a pore-forming module. The lectin module has a beta-trefoil scaffold that bears structural similarities to those present in toxins known to interact with galactose-related carbohydrates such as the hemagglutinin component (HA1) of the progenitor toxin from Clostridium botulinum, abrin, and ricin. On the other hand, the C-terminal pore-forming module (composed of domains 2 and 3) exhibits three-dimensional structural resemblances with domains 3 and 4 of the beta-pore-forming toxin aerolysin from the Gram-negative bacterium Aeromonas hydrophila, and domains 2 and 3 from the epsilon-toxin from Clostridium perfringens. This finding reveals the existence of common structural elements within the aerolysin-like family of toxins that could be directly involved in membrane-pore formation. The crystal structures of the complexes of LSL with lactose and N-acetyllactosamine reveal two dissacharide-binding sites per subunit and permits the identification of critical residues involved in sugar binding.  (+info)

Microarray and proteomics analyses of human intestinal epithelial cells treated with the Aeromonas hydrophila cytotoxic enterotoxin. (62/265)

We performed microarray analyses on RNA from human intestinal epithelial (HT-29) cells treated with the cytotoxic enterotoxin (Act) of Aeromonas hydrophila to examine global cellular transcriptional responses. Based on three independent experiments, Act upregulated the expression of 34 genes involved in cell growth, adhesion, signaling, immune responses (including interleukin-8 [IL-8] production), and apoptosis. We verified the upregulation of 14 genes by real-time reverse transcriptase-PCR and confirmed Act-induced production of IL-8 by enzyme-linked immunosorbent assay on supernatants from nonpolarized and polarized HT-29 cells. Maximal production of IL-8 in response to Act required the presence of intracellular calcium, since chelation of calcium with BAPTA-AM significantly reduced Act-induced IL-8 production in HT-29 cells. We also examined activation of mitogen-activated protein kinases and, as demonstrated by Western blot analysis of apical side-treated polarized HT-29 cells, Act induced phosphorylation of p38, c-Jun NH(2)-terminal kinase, and extracellular signal-regulated kinase 1/2. In addition, KinetWorks proteomics screening of whole-cell lysates revealed Act-induced phosphorylation of cyclic AMP-response element binding protein (CREB), c-Jun, adducin, protein kinase C, and signal transducer and activator of transcription 3 (STAT3) and decreased phosphorylation of protein kinase Balpha, v-raf-1 murine leukemia viral oncogene homolog 1 (i.e., Raf1), and STAT1. We verified activation of CREB and activator protein 1 in polarized cells by gel shift assay. This is the first description of human intestinal epithelial cell transcriptional alterations, phosphorylation or activation of signaling molecules, cytokine production, and calcium mobilization in response to this toxin.  (+info)

Dramatic broadening of the substrate profile of the Aeromonas hydrophila CphA metallo-beta-lactamase by site-directed mutagenesis. (63/265)

Among class B beta-lactamases, the subclass B2 CphA enzyme is characterized by a unique specificity profile. CphA efficiently hydrolyzes only carbapenems. In this work, we generated site-directed mutants that possess a strongly broadened activity spectrum when compared with the WT CphA. Strikingly, the N116H/N220G double mutant exhibits a substrate profile close to that observed for the broad spectrum subclass B1 enzymes. The double mutant is significantly activated by the binding of a second zinc ion under conditions where the WT enzyme is non-competitively inhibited by the same ion.  (+info)

Identification and characterization of putative virulence genes and gene clusters in Aeromonas hydrophila PPD134/91. (64/265)

Aeromonas hydrophila is a gram-negative opportunistic pathogen of animals and humans. The pathogenesis of A. hydrophila is multifactorial. Genomic subtraction and markers of genomic islands (GIs) were used to identify putative virulence genes in A. hydrophila PPD134/91. Two rounds of genomic subtraction led to the identification of 22 unique DNA fragments encoding 19 putative virulence factors and seven new open reading frames, which are commonly present in the eight virulence strains examined. In addition, four GIs were found, including O-antigen, capsule, phage-associated, and type III secretion system (TTSS) gene clusters. These putative virulence genes and gene clusters were positioned on a physical map of A. hydrophila PPD134/91 to determine their genetic organization in this bacterium. Further in vivo study of insertion and deletion mutants showed that the TTSS may be one of the important virulence factors in A. hydrophila pathogenesis. Furthermore, deletions of multiple virulence factors such as S-layer, serine protease, and metalloprotease also increased the 50% lethal dose to the same level as the TTSS mutation (about 1 log) in a blue gourami infection model. This observation sheds light on the multifactorial and concerted nature of pathogenicity in A. hydrophila. The large number of putative virulence genes identified in this study will form the basis for further investigation of this emerging pathogen and help to develop effective vaccines, diagnostics, and novel therapeutics.  (+info)