Browsing by Author "D.V. Singh"

Now showing 1 - 20 of 26

Adherence of haemagglutinating and non-haemagglutinating clinical and environmental isolates of Aeromonas.
(1993) D.V. Singh; R.S. Dubey; S.C. Sanyal
Twelve haemagglutinating and non-haemagglutinating isolates of Aeromonas spp., comprising 6 each of clinical and environmental origin, were examined for their ability to adhere to rabbit intestinal epithelium, for inhibition of adhesion with sugars, and for delineation of the portion of intestine, jejunum, or ileum that is most susceptible to adhesion. Although the environmental isolates of Aeromonas haemagglutinated human erythrocytes that were inhibited by D-mannose and/or L-fucose, the majority of the clinical isolates of Aeromonas adhered to rabbit intestinal epithelium in almost equal proportions regardless of their haemagglutination (HA) properties, species designation, and source of isolation. Adhesion of both haemagglutinating and non-haemagglutinating isolates of Aeromonas was inhibited by sugars; however, the ability of sugar inhibition to adhere was similar to that observed with HA. This study suggests that adhesion is probably mediated by a variety of pilus or non-pilus colonisation factors which may or may not be a haemagglutinin. The jejunum was found to be more susceptible to adhesion than the ileum. However, no appreciable difference was observed in the number of adhered bacteria to adjacent loops.
Antibiotic resistance in clinical and environmental isolates of aeromonas spp
(1994) D.V. Singh; S.C. Sanyal
[No abstract available]
Attachment of non-culturable toxigenic Vibrio cholerae O1 and non-O1 and Aeromonas spp. to the aquatic arthropod Gerris spinolae and plants in the River Ganga, Varanasi
(1995) B.N. Shukla; D.V. Singh; S.C. Sanyal
Non-cultivable, pathogenic O1 and non-O1 Vibrio cholerae and Aeromonas spp. were resuscitated from aquatic arthropods and plant homogenate respectively, by rabbit ileal loop (RIL) assay. These organisms adhered to the aquatic arthropod Gerris spinolae and various species of phytoplankton in the River Ganga, but failed to grow after direct inoculation on artificial media except for only 10 homogenates of the arthropod. The number of non-O1 V. cholerae and Aeromonas recovered on direct inoculation of G. spinolae homogenates were in the order of 105-106 whereas those of the Ganga water were 102-103 ml-1. A total of 119 strains of O1 and non-O1 V. cholerae and Aeromonas spp. (69 isolates from G. spinolae and 50 from aquatic plants) were recovered from the loop contents. The results indicate that production of the enzyme chitinase by O1 and non-O1 V. cholerae and Aeromonas spp. might facilitate their adsorption and multiplication on different species of zoo- and phyto-plankton. Most of the isolates were enterotoxic, haemolytic and resistant to different antibiotics. This study suggests that species of zoo- and phyto-planktons, until now not reported to be associated with O1 and non-O1 V. cholerae, may act as reservoirs of these organisms as well as different species of Aeromonas in a fresh-water riverine ecosystem. © 1995.
Biochemical characteristics and enterotoxicity of Aeromonas species isolated from man and environment.
(1992) D.V. Singh; S.C. Sanyal
A total of 147 isolates of Aeromonas spp., of which 54 were isolated from children and adults with diarrhoea, 44 from variety of water sources and 49 from environmental sources, were tested for enterotoxin production and its correlation with biochemical characters. Lysine was decarboxylated by 38% of A. hydrophila, 35% of A. sobria and 20% of A. caviae. Majority strains were unable to utilise citrate as the sole source of carbon except one of A. hydrophila, 8 of A. sobria and 6 of A. caviae. Beta-haemolysis was shown by 108 isolates that included 79% of A. hydrophila, 76% of A. sobria and 70% A. caviae. About 56% of Aeromonas strains including A. caviae caused fluid accumulation in the rabbit ileal loop in the initial tests and the remaining did so after 1-3 consecutive passages. Enterotoxin production did not correlate with the positive biochemical characters such as Voges-Prauskauer reaction, lysin decarboxylation, haemolysin production, citrate utilisation and failure to ferment arabinose either singly or in combination. This study indicates that enterotoxicity of Aeromonas may not be correlated with any of the biochemical characters either singly or in combination.
Candidate live oral cholera vaccine strains produce a new cholera toxin
(1996) D.V. Singh; Anjali Tikoo; S.C. Sanyal
When six candidate live oral cholera vaccine strains deleted for one or all known virulence factors are tested for enterotoxin production, two of them caused fluid accumulation in the initial rabbit ileal loop (RIL) test, the others did so after 1-3 serial passages through RIL. Culture filtrates also showed similar secretory response. Ten times concentrated culture filtrates of these strains gave precipitin band against anti-new cholera toxin showing reaction of identity. These observations clearly indicate that vaccine strains produce a secretogen antigenically similar to the new cholera toxin.
Characterization of Vibrio cholerae O139 belonging to multiple ribotypes and isolated from diarrhoeal patients in Kerala, southern India
(2011) M.H.U. Turabe Fazil; R. Bhanumathi; H.P. Pandey; D.V. Singh
Twenty-four Vibrio cholerae O139 strains isolated from Kerala, southern India were characterized by PCR, CTX typing and ribotyping; all of which, except three strains, carried the core of the CTX genetic element, colonization-toxin co-regulated pilus, the adherence outer membrane protein, haemolysin, central regulatory protein encoded toxR, SXT genetic element, and produced cholera toxin and biofilm. Results of RFLP analysis revealed twenty-one of the O139 strains possess two copies of CTXΦ and pre-CTXF{cyrillic} always preceded by tandemly arranged RS1 element; one had two copies of pre-CTXΦ and two a single copy of pre-CTXΦ. Nucleotide sequencing detected classical ctxB in CTXETΦ and CTXCalcF{cyrillic} with additional change at 28th amino acid position of CTXCalcF{cyrillic}. Ribotype analysis revealed the presence of multiple ribotypes, including B-I and B-II, and new ribotypes designated B-VIIIa, B-VIIIb and B-IX, not reported earlier among V. cholerae O139 strains. These observations thus indicate that genetic recombination or mutations had occurred in conserved rrn operon and variations in CTXΦ may have implications on the evolution of the organism. © 2010 Elsevier B.V.
Development of an improved synthetic medium for a better production of the new cholera toxin and its immunological relationship with the toxin produced by Vibrio cholerae O139 strains
(Blackwell Publishing Ltd, 1996) Anjali Tikoo; D.V. Singh; B.N. Shukla; S.C. Sanyal
An improved synthetic medium (M4) comprising syncase medium supplemented with sodium chloride (1%) and sucrose (0.5%) pH adjusted to 7.4 was developed for a better production of the new cholera toxin (NCT). The culture filtrates prepared in the M4 medium caused significantly (P < 0.05) more fluid accumulation than that in syncase medium. Crude toxin, prepared in the M4 medium with V. cholerae O1 strains (X-392 and 2740-80) caused a reaction similar to that of the same amount of NCT (32 μg) prepared in the syncase medium. The neutralization of the optimal loop reacting dose of the NCT prepared in the M4 medium by anti-NCT raised against syncase prepared toxin indicates the release of the same kind of toxin in both media. These observations indicate that the modified M4 medium may be used for NCT preparation and further characterization All the strains of Vibro cholerae O139 used in this study produced a toxin-antigenically similar to NCT.
Enteropathogenicity of Aeromonas jandaei and A. trota
(1997) D.V. Singh; S.C. Sanyal
An experimental study of five isolates of Aeromonas jandaei and 12 of A. trota was carried out to examine if they produced an enterotoxic substance, and if so, to characterise that factor and to see if it caused any mucosal damage. Only two of the A. trota strains caused fluid accumulation in the initial rabbit ileal loop (RIL) tests. The remaining strains did so only after one to five sequential passages through RILs and once they caused a secretory response they showed a gradual enhancement of fluid outpouring after each subsequent passage. Inocula of ~ 1 x 105 viable cells and 0.25 ml of culture filtrate caused fluid accumulations comparable to those of toxigenic C. cholerae 569B. The enterotoxic factors of both organisms were inactivated when held at 56°C for 20 min or 65°C for 10 min and showed biological activity over a wide range of pH. The only histopathological change observed in the ileal loop was depletion of mucus from the goblet cells. These data thus indicate that strains of A. jandaei and A. trota may produce a heat-labile and pH-stable diarrhoeagenic substance that causes little or no damage to the intestinal mucosa, like that of other known heat-labile enterotoxins.
Enterotoxicity of clinical and environmental isolates of Aeromonas spp.
(1992) D.V. Singh; S.C. Canyal
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 < 0.05). Furthermore, the environmental strains of H. hydrophila and A. sobria produced more fluid than the clinical isolates (p < 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.
Enterotoxicity, haemolytic activity and antibiotic susceptibility of Aeromonas eucrenophila strains isolated from water and infected fish
(1997) D.V. Singh; S.C. Sanyal
Strains of A. eucrenophila isolated from fresh water (2 strains) and infected fish (4 strains) were tested for haemolytic activity and enterotoxicity and any correlation between them. Also, the resistance patterns of A. eucrenophila were tested especially in relation to ampicillin. None of the A. eucrenophila strains caused fluid accumulation in the initial tests, however, they did so only after one to four sequential passages through the gut of a susceptible host. All the strains of A. eucrenophila showed β-haemolytic activities. Production of β-haemolysin could be correlated with enterotoxicity. Since all the strains of A. eucrenophila were resistant to ampicillin, media containing this antibiotic may be used for their isolation from diverse sources.
Haemagglutinating activity, serum sensitivity and enterotoxigenicity of Aeromonas spp.
(1993) D.V. Singh; S.C. Sanyal
Of 97 isolates of Aeromonas spp. that were examined for haemagglutination (HA) and enterotoxigenicity, 35 were from clinical and 62 from environmental sources; 66 of them were also screened for sensitivity to normal human serum (NHS). HA was caused by 44 isolates (45%); it was unrelated to the source of the strain, but it was caused by a higher proportion of the isolates of A. hydrophila than of A. sobria or A. caviae. Of the haemagglutinating strains, 82% were enterotoxigenic, whereas most of the non-haemagglutinating strains were non-toxigenic when tested initially. All the latter became enterotoxin producers after serial passage through rabbit ileal loops, but without change in HA. Most (64%) of the isolates, including 68% of A. caviae (72% of clinical and 65% of environmental), were resistant to the bactericidal action of NHS. Most (92%) of the serum-sensitive strains were killed by activation of both the classical and alternate pathways of complement, the others only by the alternate pathway. Most (74%) of the serum-resistant strains caused fluid accumulation in the initial tests in ileal loops, regardless of species or source. Haemagglutinating and serum-resistant strains caused significantly more accumulation of fluid (p < 0.05) than non-haemagglutinating and serum-sensitive strains. This study shows partial correlation between HA or serum sensitivity and enterotoxigenicity, but the properties are probably not genetically linked.
Haemolysin and enterotoxin production by Aeromonas caviae isolated from diarrhoeal patients, fish and environment.
(1992) D.V. Singh; S.C. Sanyal
Beta-haemolytic activity was shown by 46 (63%) of the 73 Aeromonas caviae strains isolated from diverse sources, such as diarrhoeal stools, fish ulcers and water in titres of 16-64 HU/ml. Only 2 strains showed alpha-haemolytic activity and the remaining 27% of them were nonhaemolytic. Live cells and culture filtrates of 60.3% of the A. caviae isolates caused accumulation of fluid in rabbit gut loops in the initial set of experiments. Of the 46 strains showing beta-haemolytic activity only 34 gave positive ileal loop reactions in the initial experiments. One of the 2 strains showed alpha-haemolytic activity and 9 of the 20 nonhaemolytic strains also caused fluid accumulation in the same set of experiments. Those strains that showed beta-haemolytic activity caused significantly more (p less than 0.01) fluid outpouring than the alpha- or nonhaemolytic isolates regardless of their sources of origin. Twenty-nine (39.7%) strains that showed alpha-, beta-, and nonhaemolytic activity and caused little or no fluid accumulation in initial experiments did so after 1-3 consecutive passages through rabbit gut. The nontoxic strain showing alpha- and non-haemolytic activity switched over to production of beta-haemolytic activity once their live cells gave positive loop reactions. However, on repeated subcultures or on preservation in the laboratory for 2-3 weeks, all of them reverted back to their original nontoxic haemolytic types, i.e. alpha- or nonhaemolytic activity.
Haemolysin produced by Vibrio cholerae non-O1 is not enterotoxic
(Microbiology Society, 1996) D.V. Singh; B.N. Shukla; S.C. Sanyal
Of 28 isolates of Vibrio cholerae non-O1 (10 from diarrhoeal patients and 18 from environmental sources) examined for haemolytic activity and its correlation, if any, with enterotoxic activity, 24 showed haemolysis. The four non-haemolytic isolates showed haemolysis after consecutive passages through rabbit ileal loops (RILs). The titres of haemolytic activity were 4-64 HU/ml irrespective of their source. Eight (28.5%) of the non-O1 isolates caused fluid accumulation; six (25%) were haemolytic and two (50%) non-haemolytic. The remaining isolates showed enterotoxic activity after one-to-three consecutive passages through RILs irrespective of their haemolytic character and source. Environmental isolates caused significantly more fluid accumulation than the diarrhoeal isolates. All these isolates reverted to their original non-toxigenic character on repeated subculture or on storage in the laboratory, but continued to show haemolytic activity. The results of the present study indicate that V. cholerae non-O1 strains are potentially enterotoxigenic independent of their haemolytic character and source, and enterotoxin, not haemolysin, is the factor most likely to be responsible for their enterotoxic activity.
Identification of host plant resistant to Dolichos Yellow Mosaic Virus (DYMV) in Dolichos bean (Lablab purpureus)
(2012) P.K. Singh; Ashish Kumar; N. Rai; D.V. Singh
Three hundred Dolichos bean (Lablab purpureus) genotypes were screened against Dolichos Yellow Mosaic Virus (DYMV) disease. Initial screening was done under field conditions where disease incidence was calculated for each genotype. Subsequently, selfed progenies of 34 symptomless lines were challenged by sap inoculation under field conditions, out of which only three genotypes, viz. VRSEM-894, VRSEM-887 and VRSEM-860 did not show any symptoms. Using root stalk of susceptible genotype (Ankur Goldy), these three putative symptomless genotypes were further challenged by grafting. The resistant reactions of VRSEM-894, VRSEM-887 and VRSEM-860 were confirmed as even after 60 days of successful grafting, no viral symptom appeared on all the grafted plants of these genotypes. When subjected to PCR amplification with DYMV coat protein gene specific primer, these three symptomless genotypes did not show any amplification, suggesting that there was no infection of Dolichos Yellow Mosaic Virus in those genotypes.
Impact of urea on spatio-temporal distribution of methanotrophic bacteria in rainfed rice agro ecosystem
(2011) B. Singh; D. Katiyar; D.V. Singh; A.K. Kashyap; A.M. Lall
Rice fields are one of the major biogenic sources of atmospheric methane. Apart from this contribution to the greenhouse effect, rice paddy soil represents a suitable model system to study fundamental aspects of microbial ecology, such as diversity, structure and dynamics of microbial communities as well as structure function relationships between microbial groups. The present study was conducted in rainfed rice fields planted to rice (Oryza sativa) cultivar, NDR-97, to evaluate the variation of population of Methane Oxidizing Bacteria (MOB) in different soil type (Bare, Bulk and rhizosphere) over a period of 13 weeks. Urea was the only fertilizer applied, at a rate of 100 kg N ha -1 in three split doses. The experiment was laid out in a randomized complete block design with three replicate plots for treatments. The soil exhibited higher numbers of MOB in control plots of bulk and rhizospheric (37.4xl0 6 and 58.87xl0 6 cells g -1 dry soil) than in plots treated with urea (28.6xl0 6 and 51.9x10 6 cells g -1 dry soil) at 80 Days after Sowing (DAS) and were highest in the rhizospheric soil (58.87xl0 6 cells g -1 dry soil) followed by bulk (37.4xl0 6 cells g -1 dry soil) and bare (2.2xl0 6 cells g -1 dry soil) in unfertilized soil but bare (control) soil was attained highest MOB (2.7xl0 6 cells g -1 dry soil) on 40 DAS and MOB significantly decreased in fertilized soil. The concentrations of NH 4 +-N were significantly (p<0.05) lower in the rhizosphere (1.3 μg g -1 soil) than in bulk (3.7 μg g -1 soil) and bare soils (4.1 μg g -1 soil) on 80 DAS in unfertilized plots. In fertilized soil NH 4 +-N concentration were increased due to lower number of population at different day's intervals. The study suggests that the development of the rice rhizosphere brings about a spatial pattern in the distribution of methanotrophic bacteria which increases in size, over time; within the rhizosphere and adjoining bulk soil and that the rhizosphere is a potential microsite of methanotrophic bacterial activity. © 2011 Academic Journals Inc.
Influence of animal passage on haemolysin and enterotoxin production in Vibrio cholerae O1 biotype El Tor strains
(Microbiology Society, 1994) A. Tikoo; D.V. Singh; S.C. Sanyal
Of 43 strains of Vibrio cholerae O1 biotype El Tor isolated over a span of almost three decades (1964-1990) from stools of children and adults with diarrhoea (25 isolates) and from sewage (three) and water from the river Ganges (15) examined for production of haemolysin and its correlation with enterotoxin production, 17 isolates showed haemolysis. The majority of isolates (26), including 68% of diarrhoeal and 50% of environmental origin, were non-haemolytic. The titre of haemolysin produced was 4-16 HU/ml, irrespective of the source of isolation. Haemolytic strains caused significantly more fluid accumulation than the non-haemolytic strains in the rabbit ileal loop (RIL) test. Twenty nine (67.4) V. cholerae biotype El Tor isolates-all the haemolytic and most (61.5%) of the non-haemolytic isolates tested-caused fluid accumulation. The remaining non-haemolytic strains that caused little or no accumulation of fluid did so after one to four consecutive passage(s) through RIL without change in haemolytic character; these strains required more consecutive passage through rabbit gut to show haemolysis. All these strains reverted to their original non-haemolytic character on repeated subculture or on storage in the laboratory but continued to show enterotoxic activity. The present study indicated that El Tor haemolysin is not responsible for fluid accumulation in rabbit gut.
Influence of NaCl on photosynthesis and nitrogen metabolism of cyanobacterium Nostoc calcicola
(Maik Nauka Publishing / Springer SBM, 2015) V. Singh; K.D. Pandey; S. Mesapogu; D.V. Singh
Nostoc calcicola, a halotolerant alkaliphilic, nitrogen-fixing cyanobacterium, was grown under various NaCl concentrations (from 500 to 2000 mM) at alkaline pH. In cyanobacteria, physiological and biochemical responses were correlated with the external salt stress. The optimal condition for cell growth of N. calcicola isolated from alkaline ‘Usar’ soils of northern India was 500 mM NaCl at pH 10.5, accompanied with an increase in photosynthetic O2 evolution, carbohydrate content and activities of nitrate reductase, glutamine synthetase, photosystem I and photosystem II. Under salt stress conditions above 500 mM NaCl, cell growth and carbohydrate contents reduced. The results indicate that production of carbohydrates under salinity stress at alkaline pH acts as major mechanism of salt tolerance in cyanobacteria. © 2015, Pleiades Publishing, Inc.
Isolation and characterization of salinity resistant mutant of a nitrogen‐fixing cyanobacterium, Anabaena doliolum
(1991) D.V. Singh; A.K. Tripathi; H.D. Kumar
D.V. SINGH. A.K. TRIPATHI AND H.D. KUMAR. 1991. Sodium chloride, up to 20 mmol/l concentration, had a positive effect on acetylene reducing activity and photosynthetic oxygen evolution of a paddy field cyanobacterium, Anabaena doliolum. Beyond 20 mmol/l level of salinity adverse effects appeared. A mutant resistant to 200 mmol/l NaCl was isolated by nitrosoguanidine mutagenesis. The mutant, NaCl‐R200, showed about 20–25% more nitrogenase activity and photosynthetic oxygen evolution than the parent. Better capacity of nitrogen fixation and photosynthesis possibly could help the mutant in synthesis of osmotic stabilizer to resist the salinity stress. Copyright © 1991, Wiley Blackwell. All rights reserved
Molecular characterization of Vibrio cholerae O139 Bengal isolated from water and the aquatic plant Eichhornia crassipes in the River Ganga, Varanasi, India
(2003) R. Bhanumathi; F. Sabeena; Sree Renjini Isac; B.N. Shukla; D.V. Singh
A collection of ten strains of Vibrio cholerae O139, comprising six isolates from Eichhornia crassipes, two from water of the River Ganga, and one each from a well and a hand pump, were characterized. All the strains carried the CTX genetic element (ctxA, zot, and ace) except for the st gene and carried structural and regulatory genes for toxin-coregulated pilus (tcpA, tcpI, and toxR), adherence factor (ompU), and accessory colonization factor (acfB); all produced cholera toxin (CT). These strains were resistant to trimethoprim, sulfamethoxazole, streptomycin, and to the vibriostatic agent pteridine. Results obtained by ribotyping and enterobacterial repetitive intergenic consensus sequence-PCR fingerprint analysis indicate that multiple clones of toxigenic-pathogenic V. cholerae O139 were present in the aquatic environment.
Production of chitinase by enterotoxigenic Aeromonas species isolated from clinical and environmental sources.
(1992) D.V. Singh; S.C. Sanyal
Thirty-six isolates of Aeromonas, 13 from children and 23 from the environment were tested for production of chitinase in culture supernatants. Thirty-four isolates of the three species (91% clinical and 96% environmental) produced constitutive chitinase. The environmental isolates elaborated significantly more (p < 0.005) of the enzyme than those from the children. Four of the environmental isolates also produced inducible chitinase. All isolates of Aeromonas were enterotoxic, however, the isolates producing inducible chitinase showed significantly higher enterotoxic activity. This study indicates that there is correlation between production of enterotoxin and chitinase in Aeromonas species.