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Biomedical subjects

M S Islam

Publications and source records attributed to M S Islam.

At least 37 records · Page 2Linked to original sources
PubMed2001

Survival of Shigella dysenteriae type 1 on fomites.

Studies have shown that various objects, such as utensils, toys, and clothes, can serve as vehicles for transmission of Shigella spp. Shigellae can become viable but non-culturable (VBNC) when exposed to various environmental conditions as shown in earlier studies. The present study was carried out to detect VBNC Shigella dysenteriae type 1 on various fomites by direct viable counting, polymerase chain reaction (PCR), and fluorescent antibody methods. S. dysenteriae type 1 was inoculated onto cloth, wood, plastic, aluminum, and glass objects. Results showed that 1.5-4.0 hours after inoculation, S. dysenteriae type 1 became non-culturable, and after five days, non-culturable but viable S. dysenteriae type 1 could be detected by both PCR and fluorescent antibody techniques. Fomites can be considered an important potential route of transmission of VBNC S. dysenteriae type 1 and a significant factor in the epidemiology of shigellosis.

Bangladesh↗
PubMed2001

Modification of the multiplex PCR for unambiguous differentiation of the El Tor & classical biotypes of Vibrio cholerae O1.

BACKGROUND & OBJECTIVES: Biotyping of Vibrio cholerae O1 using multiplex PCR (ctxA-tcpA) exploits the nucleotide sequence differences of the major subunit protein of the toxin co-regulated pilus (TCP) gene (tcpA) to differentiate between the classical and El Tor biotypes. However, the presence of classical biotype specific tcpA amplicon with the El Tor strains often complicates the interpretation. The effect of PCR variables on the amplification of biotype specific tcpA in the multiplex PCR has been investigated. METHODS: Reference strains of toxigenic V. cholerae O1 belonging to classical and El Tor biotypes were selected to optimize the PCR variables for the unambiguous biotype determination by multiplex PCR. RESULTS: In the multiplex PCR assay, a reduction in the reaction volume from 100 microliters to 25 microliters and the annealing temperature of 64 degrees C, the El Tor strain produced ctxA amplicon (302 bp) along with tcpA amplicons of 618 bp and 472 bp which are specific for classical and El Tor tcpA respectively. The simplex PCR with biotype specific tcpA primer pairs showed the amplification of either 472 bp or 618 bp tcpA amplicon with El Tor template. With the classical biotype strain, the specific primer pair yielded tcpA amplicon of the expected size. Lowering of PCR annealing temperature from 64 to 60 degrees C resulted in the elimination of the amplification of the nonspecific tcpA amplicon with El Tor strain. INTERPRETATION & CONCLUSION: A comparison of the theoretical melting temperature (Tm) values of the reacting primers, and their alignment to the biotype specific tcpA revealed the basis of unambiguous biotyping of V. cholerae O1 at a PCR annealing temperature of 60 degrees C.

Bacterial Outer Membrane Proteins↗
PubMed2000

Fetal pancreatic islets express functional leptin receptors and leptin stimulates proliferation of fetal islet cells.

OBJECTIVE: Previous studies have demonstrated that leptin can stimulate proliferation of insulin-secreting tumor cell lines. The objective of this study was to characterize whether leptin could stimulate proliferation of primary beta-cells too. Since adult beta-cells have very limited capacity for replication, we examined the effect of leptin on islets of Langerhans obtained from fetal rats, in a tissue culture system. METHODS: Leptin receptor mRNA and c-fos mRNA were measured by RT-PCR. Proliferation of fetal rat islet cells was measured by a WST-1 colorimetric assay and [3H]-thymidine incorporation assay. RESULTS: Leptin stimulated proliferation of serum-deprived fetal rat islet cells, as indicated by increased formation of formazan dye from a tetrazolium salt WST-1. Leptin stimulated DNA synthesis in islet cells, as indicated by increased [3H]-thymidine incorporation into DNA. The effect of leptin on islet cell proliferation was on average 39-50% of the effect obtained with 10% fetal bovine serum. Leptin increased c-fos mRNA expression by 2.8-fold in isolated fetal islets after 30 min treatment. In fetal pancreatic islets, both the common extracellular portion (OB-R) and the intact long form (OB-Rb) of the leptin receptor were readily detected by reverse transcriptase polymerase chain reaction. CONCLUSION: Functional leptin receptors are expressed in pancreatic islet cells, as early as during the fetal stage of development of these microorgans. Leptin stimulates proliferation of fetal islet cells and might play a role in determining islet cell mass at birth.

Animals↗
PubMed2000

Prevalence of enterotoxin genes in Aeromonas spp. isolated from children with diarrhea, healthy controls, and the environment.

Aeromonads are causative agents of a number of human infections. Even though aeromonads have been isolated from patients suffering from diarrhea, their etiological role in gastroenteritis is unclear. In spite of a number of virulence factors produced by Aeromonas species, their association with diarrhea has not been clearly linked. Recently, we have characterized a heat-labile cytotonic enterotoxin (Alt), a heat-stable cytotonic enterotoxin (Ast), and a cytotoxic enterotoxin (Act) from a diarrheal isolate of Aeromonas hydrophila. Alt and Ast are novel enterotoxins which are not related to cholera toxin; Act is aerolysin related and has hemolytic, cytotoxic, and enterotoxic activities. We studied the distribution of the alt, ast, and act enterotoxin genes in 115 of 125 aeromonads isolated from 1, 735 children with diarrhea, in all 27 aeromonads isolated from 830 control children (P = 7 x 10(-4) for comparison of rates of isolation of aeromonads from cases versus those from controls), and in 120 randomly selected aeromonads from different components of surface water in Bangladesh. Aeromonas isolates which were positive only for the presence of the alt gene had similar distributions in the three sources; the number of isolates positive only for the presence of the ast gene was significantly higher for the environmental samples than for samples from diarrheal children; and isolates positive only for the presence of the act gene were not found in any of the three sources. Importantly, the number of isolates positive for both the alt and ast genes was significantly higher for diarrheal children than for control children and the environment. Thus, this is the first study to indicate that the products of both the alt and ast genes may synergistically act to induce severe diarrhea. In 26 patients, Aeromonas spp. were isolated as the sole enteropathogen. Analysis of clinical data from 11 of these patients suggested that isolates positive for both the alt and ast genes were associated with watery diarrhea but that isolates positive only for the alt gene were associated with loose stools. Most of the isolates from the three sources could be classified into seven phenospecies and eight hybridization groups. For the first time, Aeromonas eucrenophila was isolated from two children, one with diarrhea and another without diarrhea.

Aeromonas↗
PubMed1999

Is radiosensitive cell line cross-sensitive to heat?: Effect of heat on two rat yolk sac tumor cell lines with different radiosensitivity.

The differences between two rat yolk sac tumor cell lines, which are of the same origin but differ in their response to irradiation, in thermal sensitivity and development of thermotolerance were investigated. A radiosensitive cell line NMT-1 is consistently less heat sensitive than the radioresistant cell line NMT-1R. The thermotolerances in NMT-1 and in NMT-1R preheated at 43 degrees C for 30 min, respectively, reached peaks at 6 h and at 12 h, but did not completely disappear at 48 h. Thermotolerance with a good correlation between both cell lines with HSP70 accumulation was observed in a different time course after a primary heating.

Animals↗
PubMed1999

Cross-reaction between a strain of Vibrio mimicus and V. cholerae O139 Bengal.

Of 200 isolates of Vibrio mimicus screened, one from water (N-57) agglutinated with V. cholerae O139 polyclonal antiserum (absorbed with a rough strain of V. cholerae only) and not with O139 polyclonal diagnostic antiserum (absorbed with the rough strain and V. cholerae O22 and O155). The antigenic relationship between V. cholerae 0139 and N-57 is of a,b-a,c type, where a is the common antigenic epitope and b and c are unique epitopes. Strain N-57 was assigned to a new serogroup of V. cholerae O194. It gave negative results in a monoclonal antibody-based rapid test and a PCR test specific for V. cholerae O139. It did not possess the ctx gene or produce cholera toxin. Antiserum to strain N-57 cross-protected infant mice against cholera on challenge with V. cholerae O139. Structural studies of the surface polysaccharides and studies of the rfb genes will shed more light on the extent of relatedness between V. mimicus N-57 and V. cholerae O139.

Agglutination Tests↗
PubMed1999

Pulsed electromagnetic fields for the treatment of bone fractures.

The effectiveness of electrical stimulation and Pulsed Electro Magnetic Field (PEMF) stimulation for enhancement of bone healing has been reported by many workers. The mechanism of osteogenesis is not clear, therefore, studies look for empirical evidence. The present study involved a clinical trial using low amplitude PEMF on 19 patients with non-union or delayed union of the long bones. The pulse system used was similar in shape to Bassett's single pulse system where the electric voltage pulse was 0.3 mSec wide repeating every 12 mSec making a frequency of about 80 Hz. The peak magnetic fields were of the order of 0.01 to 0.1 m Tesla, hundred to thousand times smaller than that of Bassett. Among the 13 who completed this treatment schedule the history of non-union was an average of 41.3 weeks. Within an average treatment period of 14 weeks, 11 of the 13 patients had successful bone healing. The two unsuccessful cases had bone gaps greater than 1 cm following removal of dead bone after infection. However, use of such a low field negates Bassett's claim for a narrow window for shape and amplitude of wave form, and justifies further experimental study and an attempt to understand the underlying mechanism.

Adolescent↗
PubMed1998

Cell signaling by the type IV pili of pathogenic Neisseria.

Neisseria gonorrhoeae and Neisseria meningitidis are Gram-negative bacterial pathogens that infect human mucosal epithelia. Type IV pilus-mediated adherence of these bacteria is a crucial early event for establishment of infection. In this work, we show that the type IV pili transduce a signal into the eucaryotic host cell. Purified adherent pili, but not pili from a low binding mutant, trigger an increase in the cytosolic free calcium ([Ca2+]i) in target epithelial cells, a signal known to control many cellular responses. The [Ca2+]i increase was blocked by antibodies against CD46, a putative pilus receptor, suggesting a role for this protein in signal transduction. Pilus-mediated attachment was inhibited by depletion of host cell intracellular Ca2+ stores but not by removal of extracellular Ca2+. Further, kinase inhibition studies showed that pilus-mediated adherence is dependent on casein kinase II. In summary, these data reveal a novel function of the type IV pili, namely induction of signal transduction pathways in host cells.

Antigens, CD↗
PubMed1998

In situ activation of the type 2 ryanodine receptor in pancreatic beta cells requires cAMP-dependent phosphorylation.

Molecular mechanisms that regulate in situ activation of ryanodine receptors (RY) in different cells are poorly understood. Here we demonstrate that caffeine (10 mM) released Ca2+ from the endoplasmic reticulum (ER) in the form of small spikes in only 14% of cultured fura-2 loaded beta cells from ob/ob mice. Surprisingly, when forskolin, an activator of adenylyl cyclase was present, caffeine induced larger Ca2+ spikes in as many as 60% of the cells. Forskolin or the phosphodiesterase-resistant PKA activator Sp-cAMPS alone did not release Ca2+ from ER. 4-Chloro-3-ethylphenol (4-CEP), an agent that activates RYs in other cell systems, released Ca2+ from ER, giving rise to a slow and small increase in [Ca2+]i in beta cells. Prior exposure of cells to forskolin or caffeine (5 mM) qualitatively altered Ca2+ release by 4-CEP, giving rise to Ca2+ spikes. In glucose-stimulated beta cells forskolin induced Ca2+ spikes that were enhanced by 3,9-dimethylxanthine, an activator of RYs. Analysis of RNA from islets and insulin-secreting betaTC-3-cells by RNase protection assay, using type-specific RY probes, revealed low-level expression of mRNA for the type 2 isoform of the receptor (RY2). We conclude that in situ activation of RY2 in beta cells requires cAMP-dependent phosphorylation, a process that recruits the receptor in a functionally operative form.

Animals↗
PubMed1998

Effects of ryanodine receptor agonist 4-chloro-m-cresol on myoplasmic free Ca2+ concentration and force of contraction in mouse skeletal muscle.

In single mouse skeletal muscle fibers injected with fluorescent Ca2+ indicator Indo-1, 4-chloro-m-cresol (chlorocresol, 4-CmC) and its lipophilic analogue 4-chloro-3-ethylphenol (4-CEP) increased resting myoplasmic free [Ca2+] ([Ca2+]i) in a dose-dependent manner. In this regard, 4-CEP was more potent than 4-CmC and both were more potent than caffeine. High concentrations of 4-CmC (1 mM) or 4-CEP (500 microM) caused large and irreversible increase in resting [Ca2+]i leading to contracture. 4-CmC potentiated the [Ca2+]i increase and force of contraction induced by tetanic stimulation. Unlike caffeine, 4-CmC did not affect the activity of sarcoplasmic reticulum Ca2+ pump or the myofibrillar Ca2+ sensitivity. A low concentration of 4-CEP (20 microM) had no effect on resting [Ca2+]i on its own, but it enhanced the resting [Ca2+]i increase induced by caffeine and also potentiated the [Ca2+]i increase and contraction induced by tetanic stimulation. However, a relatively high concentration of 4-CEP (200 microM) inhibited tetanic stimulation-induced [Ca2+]i increase and contraction. Dantrolene, a muscle relaxant, inhibited 4-CmC-induced [Ca2+]i increase under resting conditions. However, when 4-CEP was applied in the presence of dantrolene, there was an exaggerated increase in [Ca2+]i. We conclude that 4-CmC and 4-CEP are potent agonists that can increase [Ca2+]i rapidly and reversibly by activating ryanodine receptors in situ in intact skeletal muscle fibers. These compounds, specially 4-CmC, may be useful for mechanistic and functional studies of ryanodine receptors and excitation-contraction coupling in skeletal muscles.

Animals↗
PubMed1998

Detection of Shigellae from stools of dysentery patients by culture and polymerase chain reaction techniques.

In Bangladesh, the isolation rates of Shigella spp. range from 11% to 12% by the conventional culture technique. Since the sensitivity of this technique is low, the polymerase chain reaction (PCR) technique was used for detecting small number of Shigellae from patients' stools. Sensitivity and specificity of the two techniques were also compared. Stool samples were collected from 41 patients with dysentery who attended the Clinical Research and Service Centre of the ICDDR,B: Centre for Health and Population Research. All stool specimens were directly plated onto MacConkey, Salmonella-Shigella, Xylose lysin deoxycholate and Hectoen enteric agar media, and Shigellae were detected following standard procedures. DNA was extracted from the stool samples, and the target sequence of invasive plasmid antigen (ipa)H locus was amplified by PCR with 130 ng each of two primers (primer H8 [5'-GTTCCTTGACCGCCTTTCCGATAC-3'] and primer H15 [5'-GCCGGTCAGCCACCCTA-3']) following standard procedures. The amplified product was hybridized using an ipaH probe. The isolation rates of Shigella dysenteriae type 1, S. flexneri, S. sonnei, and S. boydii were, respectively, 17.1%, 19.5%, 4.9% and 2.4% by the conventional method. The results of the PCR technique showed that 700 bp fragment was generated in 18 of the 18 culture-positive and in 7 of the 23 culture-negative stools. One hundred twenty-three strains of Escherichia coli were also tested by PCR for identifying the enteroinvasive E. coli, but none of them yielded any positive result. This study showed that the sensitivity of the culture technique is 72% and specificity is 100%, when the PCR technique was considered as gold standard. Therefore, the PCR may be considered a more sensitive and specific technique than the conventional culture technique and has the potential to be employed in routine diagnosis of dysentery in clinical centres as well as in epidemiologic studies.

Bacteriological Techniques↗
PubMed1998

Susceptibility of the malaria vectors to insecticides in Bangladesh.

Insecticide susceptibility tests with diagnostic dosages of 4% DDT and 5% malathion concentrations conducted at field sites on the two important principal malaria vectors namely, Anopheles dirus and An. philippinensis have been reported. They are found to be susceptible to DDT and malathion. The implication of the use of insecticides in controlling malaria is also discussed.

Animals↗
PubMed1997

Rat insulinoma-derived pancreatic beta-cells express a functional leptin receptor that mediates a proliferative response.

In addition to its interaction at hypothalamic sites to affect feeding and energy expenditure, leptin has been shown to exhibit a proliferative response in erythropoietic cells. The functional leptin receptor is also present in pancreatic islets and we now demonstrate that a commonly used clonal insulin secreting beta-cell line, RINm5F, expresses high levels of the Ob-Rb mRNA. Leptin causes an increase in tyrosine phosphorylation of a number of intracellular proteins and a dose related (10 nM-200 nM) increase in expression of the immediate-early gene, c-fos. This precedes a leptin induced proliferative response in serum-deprived RINm5F cells, which suggests that leptin might be involved in the complex regulation of proliferation of the pancreatic beta-cell.

Animals↗
PubMed1997

Thiol oxidation by 2,2'-dithiodipyridine causes a reversible increase in cytoplasmic free Ca2+ concentration in pancreatic beta-cells. Role for inositol 1,4,5-trisphosphate-sensitive Ca2+ stores.

2,2'-Dithiodipyridine (2,2'-DTDP), a reactive disulphide that mobilizes Ca2+ from ryanodine-sensitive Ca2+ stores in muscle, induced a biphasic increase in cytoplasmic free Ca2+ concentration ([Ca2+]i) in pancreatic beta-cells loaded with fura 2. This increase consisted of an early transient followed by a second, slower, rise. The [Ca2+]i transient was dependent on extracellular Ca2+ and disappeared on treatment with nimodipine. The reactive disulphide caused plasma membrane depolarization, as studied by the perforated-patch configuration of the patch-clamp technique. Hence membrane depolarization and opening of the L-type voltage-gated Ca2+ channels were responsible for the first transient in [Ca2+]i. The second slower increase in [Ca2+]i was prolonged but readily reversed by the disulphide-reducing agent 1,4-dithiothreitol. This increase in [Ca2+]i was not decreased by nimodipine or by omission of extracellular Ca2+, but was eliminated when the Ins(1,4,5)P3-sensitive Ca2+ pool was first depleted by carbachol. Ryanodine or its beta-alanyl analogue did not release Ca2+ from intracellular stores, and a high concentration of ryanodine did not inhibit Ca2+ release by 2,2'-DTDP. The disulphide compound suppressed glucose metabolism and decreased the mitochondrial inner-membrane potential. We conclude that thiol oxidation by 2,2'-DTDP affects Ca2+ homeostasis in beta-cells by multiple mechanisms. However, unlike the situation in muscle, in beta-cells 2,2'-DTDP releases Ca2+ from intracellular pools by mechanisms that do not involve activation of ryanodine receptors. Instead, in these cells the Ins(1,4,5)P3-sensitive intracellular Ca2+ store comprises an alternative target for the Ca(2+)-mobilizing action of the reactive disulphide compound.

2,2'-Dipyridyl↗
PubMed1997

Characterization of Aeromonas spp. isolated from humans with diarrhea, from healthy controls, and from surface water in Bangladesh.

Aeromonas isolates from patients with diarrhea in Bangladesh (n = 69), from healthy controls (n = 11), and from surface water (n = 40) were analyzed with respect to their hybridization groups (HGs) by the aid of fatty acid methyl ester (FAME) characterization and DNA fingerprinting by AFLP, biochemical phenotypes (Phe-nePlate [PhP] types), and the production of hemolysin and cytotoxin. The aim of the investigation was to find out whether certain strains carrying virulence factors predominated among patient isolates. According to FAME and/or AFLP analysis, most human isolates were allocated to DNA HGs 4 (Aeromonas caviae) and 1 (A. hydrophila). Most environmental strains were allocated to HG8 (A. veronii biogroup sobria) and HG4 (A. caviae), and only one was of HG1. According to PhP typing, the diversity among patient isolates was lower than that among other strains, and two dominating PhP types (types BD-1 and BD-2) were identified in 29 and 30% of the patient isolates, respectively. PhP type BD-1 was also common among the environmental isolates, whereas PhP type BD-2 was only identified in two of the other isolates. Twenty-five of 26 isolates belonging to HG1 were of the same PhP type (BD-2), whereas isolates of other common HGs were more diverse according to their PhP types. Hemolytic and cytotoxin-producing strains occurred more frequently among the environmental isolates than among patient isolates. However, the hemolytic and cytotoxic activities among human isolates was strongly correlated to the HG1/BD-2 type, which, in addition, showed high cytotoxin titers (median values, 1/512 compared to 1/128 for cytotoxin-positive isolates belonging to other types). Thus, the HG1/BD-2 type may represent a pathogenic A. hydrophila type that is able to produce diarrhea in humans.

Aeromonas↗