Antibiotic resistance, virulence gene, and molecular profiles of Shiga toxin-producing Escherichia coli (STEC) non-O157 strains isolated from human stool samples, cow stool samples, and beef samples over a period of 2 years in Calcutta, India, were determined. Resistance to one or more antibiotics was observed in 49.2% of the STEC strains, with some of the strains exhibiting multidrug resistance. The dominant combinations of virulence genes present in the strains studied were stx 1 and stx 2 (44.5% of strains) and stx 1 , stx 2 , and hlyA (enterohemorrhagic E. coli hemolysin gene) (19% of strains). Only 6.4% of the STEC strains harbored eae. The diversity of STEC strains from various sources was assessed by random amplification of polymorphic DNA (RAPD). STEC strains that gave identical or nearly similar DNA fingerprints in RAPD-PCR and had similar virulence genotypes were further characterized by pulsed-field gel electrophoresis (PFGE). Identical RAPD and PFGE profiles were observed in four sets of strains, with each set comprising two strains. There was no match in the RAPD and PFGE profiles between strains of STEC isolated from cows and those isolated from humans. It appears that the clones present in bovine sources are not transmitted to humans in the Calcutta setting although these strains showed evolutionary relatedness. Maybe for this reason, STEC has still not become a major problem in India.During the past decade, Shiga toxin-producing Escherichia coli (STEC) has evolved from a clinical novelty to a global public health concern. STEC infections have been reported from over 30 countries and can cause a spectrum of human illness ranging from symptom-free carriage to severe bloody diarrhea and even life-threatening sequelae such as hemolyticuremic syndrome (HUS) (4, 31). STEC is a serologically diverse group of food-borne, zoonotic pathogens, of which the serotype O157:H7 has been epidemiologically significant worldwide because of its notoriety of being associated with lifethreatening disease (18). However, in some geographic areas, non-O157 strains are more commonly isolated from persons with diarrhea or HUS than are O157 STEC strains (40).The ability of STEC to cause serious disease in humans is related to the production of one or more Shiga-like toxins (Stx1, Stx2, or their variants), which inhibits protein synthesis of host cells, thus leading to cell death (26, 27). Additional virulence factors-including the presence of a pathogenicity island designated the locus of enterocyte effacement (LEE) and especially eae, one of the constituent genes of LEE, which is responsible for attaching and effacing lesions (17, 28)-are also shown to be necessary for STEC infection. The large plasmid of STEC O157 carries determinants characteristic for STEC that presumably harbor additional virulence factors:hlyA (the enterohemorrhagic E. coli hemolysin gene), which acts as a pore-forming cytolysin on eukaryotic cells (38); the bifunctional catalase peroxidase (KatP) (6); the etp gene cluster (36); and the secreted serin...
We investigated the prevalence of Shiga toxin-producing Escherichia coli (STEC) in hospitalized diarrhea patients in Calcutta, India, as well as in healthy domestic cattle and raw beef samples collected from the city's abattoir. Multiplex polymerase chain reaction using primers specific for stx1 and stx2 detected STEC in 18% of cow stool samples, 50% of raw beef samples, and 1.4% and 0.6% of bloody and watery stool samples, respectively, from hospitalized diarrhea patients. Various virulence genes in the STEC isolates indicated that stx1 allele predominated. Plasmid-borne markers, namely, hlyA, katP, espP, and etpD, were also identified. Bead enzyme-linked immunosorbent assay and Vero cell assay were performed to detect and evaluate the cytotoxic effect of the Shiga toxins produced by the strains. STEC is not an important cause of diarrhea in India; however, its presence in domestic cattle and beef samples suggests that this enteropathogen may become a major public health problem in the future.
Vibrio cholerae non-O1, non-O139 was isolated from natural surface waters from different sites sampled in diarrhea endemic zones in Kolkata, India. Twenty-one of these isolates were randomly selected and included in the characterization. The multiserogroup isolates were compared by their virulence traits with a group of clinical non-O1, non-O139 isolates from the same geographic area. Of the 21 environmental isolates, 6 and 14 strains belonged to Heiberg groups I and II, respectively. Three of the environmental isolates showed resistance to 2,2-diamine-6,7-diisopropylpteridine phosphate. All of the non-O1, non-O139 strains were positive for toxR, and except for one environmental isolate, none of them were positive for tcpA in the PCR assay. None of the isolates were positive for genes encoding cholera toxin (ctxA), heat-stable toxin (est), heat-labile toxin (elt), and Shiga toxin variants (stx) of Escherichia coli. Additionally, except for one environmental isolate (PC32), all were positive for the gene encoding El Tor hemolysin (hly). The culture supernatants of 86% (18 of 21) of the environmental isolates showed a distinct cytotoxic effect on HeLa cells, and some of these strains also produced cell-rounding factor. The lipase, protease, and cell-associated hemagglutination activities and serum resistance properties of the environmental and clinical isolates did not differ much. However, seven environmental isolates exhibited very high hemolytic activities (80 to 100%), while none of the clinical strains belonged to this group. The environmental isolates manifested three adherence patterns, namely, carpet-like, diffuse, and aggregative adherence, and the clinical isolates showed diffuse adherence on HeLa cells. Of the 11 environmental isolates tested for enteropathogenic potential, 8 (73%) induced positive fluid accumulation (>100) in a mouse model, and the reactivities of these isolates were comparable to those of clinical strains of non-O1, non-O139 and toxigenic O139 V. cholerae. Comparison of the counts of the colonized environmental and clinical strains in the mouse intestine showed that the organisms of both groups had similar colonizing efficiencies. These findings indicate the presence of potentially pathogenic V. cholerae non-O1, non-O139 strains in surface waters of the studied sites in Kolkata.Vibrio cholerae non-serogroup O1 strains are ubiquitous in aquatic environments (35) and have been recognized as the causative agents of sporadic cholera-like disease and outbreaks (5,34,39,43). In addition, environmental nontoxigenic, non-O1 strains play an important role in the evolution of toxigenic V. cholerae (19). However, only a minority of the strains of V. cholerae non-O1 seem to be enteropathogenic. The pathogenicity markers of vibrios are lacking in many species, including V. cholerae non-O1, non-O139 strains. The nature of virulence and the infective doses need to be determined for the establishment of guidelines for risk assessment of each species in surface water and food material earmarked for hu...
Among Escherichia coli strains isolated from stool specimens from patients with acute diarrhea, 1.4% were found to harbor cdtB by use of enrichment cytolethal distending toxin (CDT) PCR. These isolates were identified as being enteropathogenic E. coli (EPEC). In a retrospective study using a probe hybridization assay, 6 of 138 EPEC strains were found to harbor the cdtB locus. cdtB-positive isolates mostly belong to the O86a and O127a serogroups, with the former being associated with higher expression of CDT. Pulsed-field gel electrophoresis profiles showed that the EPEC strains harboring cdtB strains are genetically diverse.Cytolethal distending toxin (CDT) is a novel class of bacterial genotoxin that induces characteristic elongation of eukaryotic cells followed by progressive cellular distention and death (12,14,23). CDT is considered to be an important factor in intestinal pathogenesis (3), as this toxin is able to induce tissue damage and fluid accumulation in the descending colon of orally infected suckling mice (21). Three genes, cdtA, cdtB, and cdtC, arranged in an apparent operon are required for the production of active CDT (25). The deduced amino acid sequences of these genes from Escherichia coli strains E6468-62 (serogroup O86) and 9142-88 (serogroup O128) are 38, 56, and 37% homologous, respectively (24, 25), and the corresponding toxins are called . The amino acid sequence of Cdt-III from strain S5 (serogroup O15) has Ͼ90% homology to Cdt-II and 55 to 69% homology to . The presence of cdt in different bacterial species (8,20,24,28) and the results of analysis of its flanking regions suggest that this gene has been acquired from heterologous species by horizontal gene transfer (7,18,22) or through a phage (13). Even though the data on the structural and functional aspects of CDT are expanding, knowledge of the epidemiological association of E. coli harboring cdt remains scanty (1,15,17,19).To investigate the incidence of cdt-harboring E. coli, a total of 284 stool specimens collected from acute-diarrhea patients of all age groups admitted to the Infectious Diseases Hospital and B. C. Roy Memorial Hospital for Children (Calcutta, India) from May to July 2002 were examined. Relevant clinical information such as presence of fever, vomiting, dehydration status, and type and duration of diarrhea was recorded for each patient. For enrichment CDT PCR, overnight stool cultures in Luria-Bertani broth (Difco, Detroit, Mich.) were directly tested for the presence of the cdtB gene in a standard PCR assay. The primer pair used in this study was based on the cdt nucleotide sequence of E. coli (25) and had the sequences 5Ј-GATTTTGCCGGGTATTTCT-3Ј and 5Ј-CCCTCAACAG AGGAAGAA-3Ј. These primers are specific for Cdt-I. After a hot start at 94°C for 5 min, the DNA was subjected to 30 cycles of denaturation at 94°C for 30 s, annealing at 55°C for 30 s, and extension at 72°C for 1 min 30 s. The expected size of the PCR amplicon was 707 bp. The sensitivity of the CDT PCR assay was 10 3 CFU. For confirmation, a PCR amplicon...
Grid computing uses software to integrate computing resources, such as CPU cycles, storage, network bandwidth, and even applications, across a distributed and heterogeneous set of networked computers. It is now widely deployed by organizations and provides seamless temporary processing-capacity expansion to handle peak-period demand on e-commerce servers, distributed gaming, and content storage and distribution. We develop a market-based resource-allocation model that adds an economic layer to the current approach of treating resource allocation as primarily a scheduling issue. We design a value-elicitation and allocation scheme that provides the economic incentives for buyers and sellers of computing resources to exchange assets. We formulate the problem as a combinatorial call auction and present a portfolio of three solution approaches that trade off economic properties, such as allocative efficiency, incentive compatibility, and fairness in allocation, with computational efficiency. The first of these is an efficient solution that maximizes social welfare and yields incentive-compatible Vickrey-Clarke-Groves prices, but requires solving multiple instances of an NP-hard problem. For markets where having a commodity price is critical, we show how the addition of fairness constraints to the efficient model can somewhat reduce the computational burden and yet preserve incentive compatibility. Finally, for markets that require real-time fast solution techniques, we propose a time-sensitive fair Grid (tsfGRID) heuristic that relaxes the maximal allocation requirement of the welfare-maximizing fair solution. Its solution is not guaranteed to be incentive-compatible, but the heuristic is designed to be fast, maintain fairness in allocations, and yield commodity prices. Notably, while incentive compatibility is not guaranteed by tsfGRID, computational results comparing it with the efficient solution technique indicate that there are no significant differences in the expected-revenue and operational-allocative characteristics.
The muscles of some important marine fishes collected in and around Hooghly estuarine coastal areas were analyzed for the heavy metals Cu, Zn, Ni, Cd, Cr and Pb. The concentration range of Cu (16.22-47.97 ppm), Pb (12.40-19.96 ppm) and Zn (12.13-44.74 ppm) were recorded comparatively higher and were similar to that found in contaminated areas. On the other hand the ranges of Ni (2.20-3.69 ppm), Cr (0-3.89 ppm) and Cd (0.62-1.20 ppm) were almost equal to those carried out over a wide range of geographical areas. The degree of bioaccumulations was metal-specific as well as species-specific in nature. The toxic groups of metals (Pb and Cd) showed higher variability than the essential metals (Cu, Zn and Ni). The calculated intake value of metals (week⁻¹ kg⁻¹ body wt) varied from 14.88 to 27.60 of Pb, 0.87 to 1.68 of Cd, 0.0 to 5.45 of Cr, 22.70 to 137.16 of Cu, 3.08 to 5.17 of Ni and 16.98 to 62.60 of Zn through human consumption of these fishes and were compared with those of standard Provisional Tolerable Weekly Intake value (PTWI) per kg body weight as stipulated by WHO. The PTWI(Cal) values of Pb in some of the fishes recorded marginally excess values and may indicate a health risk through consumption of successive 7 days in a week.
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