Identification and analysis of bacterial protein secretion inhibitors utilizing a SecA-LacZ reporter fusion system

Protein secretion is an essential process for bacterial growth, yet there are few if any antimicrobial agents which inhibit secretion. An in vivo, high-throughput screen to detect secretion inhibitors was developed based on the translational autoregulation of one of the central protein components, SecA. The assay makes use of a SecA-LacZ fusion reporter construct in Escherichia coli which is induced when secretion is perturbed. Several compounds, including two natural product extracts, which had the ability to induce the reporter fusion were identified and the MICs of these compounds for Staphylococcus aureus strain MN8 were found to be < or =128 microg/ml. Enzyme-linked immunosorbent assay, Western blotting, and immunoprecipitation techniques were used to analyze the affects of these compounds on protein secretion. Six representative compounds presented here appear to be bona fide secretion inhibitors but were found to have deleterious effects on membranes. It was concluded that, while the method described here for identifying inhibitors of secretion is valid, screens such as this, which are directed against the membrane-bound portion of a pathway, may preferentially identify compounds which affect membrane integrity.

Retrieval properties of a Hopfield model with random asymmetric interactions

The process of pattern retrieval in a Hopfield model in which a random antisymmetric component is added to the otherwise symmetric synaptic matrix is studied by computer simulations. The introduction of the anti-symmetric component is found to increase the fraction of random inputs that converge to the memory states. However, the size of the basin of attraction of a memory state does not show any significant change when asymmetry is introduced in the synaptic matrix. We show that this is due to the fact that the spurious fixed points, which are destabilized by the introduction of asymmetry, have very small basins of attraction. The convergence time to spurious fixed-point attractors increases faster than that for the memory states as the asymmetry parameter is increased. The possibility of convergence to spurious fixed points is greatly reduced if a suitable upper limit is set for the convergence time. This prescription works better if the synaptic matrix has an antisymmetric component.

Antibacterial leads from microbial natural products discovery

The accidental discovery of penicillin and the advent of sulfanilamide marked the beginning of the antibiotic era. Although synthetic compounds have continued to play important roles in the fight against bacterial infections, the contribution of microbial natural products cannot be underestimated. A vast majority of the antibacterial agents in clinical use today are either microbial natural products or one of their analogs. Finding novel chemical entities with new modes of action and optimizing their activities Microbial natural products have been a proven, rich source of novel compounds with diverse biological activities. The astounding success of the 'golden' period of the antibiotic era delivered several capable of meeting the needs of that period, and subsequently, a period of diminished commitment to finding new antibiotics was experienced. An interest in microbial natural products for other therapeutic applications continued however, and has proved rewarding. The recent increase in the emergence of antibiotic-resistant bacteria has forced many to shift their attention towards finding novel antibiotics and not surprisingly, microbial natural products are being seriously pursued as a source. New antibiotics are being isolated and the old libraries of under-exploited antibiotics are being re-examined. Novel bacterial targets are being exposed through genomics and microorganisms are being genetically engineered for novel metabolites.

Seasonality of Plasmodium vivax and P. falciparum in tribal villages in central India (1987-1995)

Microscopical examination of blood films produced from samples collected, over a 9-year period (1987-1995), from the inhabitants of four tribal villages of Mandla district, Madhya Pradesh (central India) revealed that malaria was highly endemic and probably transmitted perennially. Both Plasmodium vivax and P. falciparum were prevalent in all age-groups but their prevalence was highly seasonal: longitudinal studies showed an autumn (October-November) peak for P. falciparum and a summer (April-May) peak for P. vivax. However, both the incidence and prevalence of infection with each Plasmodium species showed inter-village variations. Analysis of the malariometric parameters investigated revealed that there had been no improvement in the malaria situation over the study period, and that, since 1992, there had been a shift in the predominant parasite, from P. vivax to P. falciparum, in each village.

Biological activity of guanacastepene, a novel diterpenoid antibiotic produced by an unidentified fungus CR115

Fermentation extracts of culture CR115, an unknown plant endophyte originally isolated from Costa Rica, were found to be active against antibiotic-resistant bacteria. The metabolite responsible for activity was identified as a novel diterpenoid antibiotic guanacastepene (mol. wt. 374.47 and mol. formula C22H30O5). Mechanistic studies done in an E. coli imp strain suggested membrane damage as the primary mode of bactericidal action. This compound also lysed human RBCs and caused leakage of intracellular potassium from E. coli imp.

Antibacterial diterpenoid acids from Azorella compacta

The two novel diterpenoid acids mulin-12,14-dien-11-on-20-oic acid (1) and mulin-12-ene-11,14-dion-20-oic acid (2) have been isolated from Azorella compacta. Their structures have been elucidated by 1D and 2D NMR methods. In contrast to the closely related known mulinolic acid (3) and its dehydration product (4) these new natural products have been shown to exhibit antimicrobial activity.

Phytochemical, morphological, and biological investigations of propolis from Central Chile

Propolis from central Chile was investigated for its plant origin by microscopical analysis of pollen grains and leaf fragments found in the sample. The pollen grains that appear with significant higher frequency in the sample corresponded to four native and two introduced species, whereas leaf fragments corresponded to four native species. Seventeen phenolic compounds that belong to the phenylpropane, benzaldehyde, dihydrobenzofuran, or benzopyran classes, were isolated from an organic extract that was found to have a moderate growth inhibitory activity against Mycobacterium avium, M. tuberculosis, and two strains of Staphylococcus aureus. The components responsible for activity were determined.

Immune responses to chloroquine--sensitive and resistant populations of Plasmodium berghei in mice

In order to elucidate the role of the host as a factor in the spread of chloroquine resistance, a study of the host's immune responses in chloroquine resistant (cqr) and chloroquine sensitive (cqs) Plasmodial infections is essential. Course of the infection and the nature of immune responses in mice infected with chloroquine resistant (R) and chloroquine sensitive (S) strains of Plasmodium berghei were compared. Crude parasite antigen activated T cells from both the groups of mice (R and S) and the parasite specific antibodies were detected in the sera of both the groups. The differences in immune responses between the control (uninfected) and infected mice were found to be significant. However, humoral and in vitro cellular responses obtained with T cells from chloroquine resistant P. berghei primed mice was lower in comparison with the responses obtained with T cells from the sensitive infections. Our studies therefore suggest that immunosuppression to parasite antigen is seen in mice primed with chloroquine resistant P. berghei, which may play a role in the development of resistance.

Nitric oxide-mediated augmentation of polymorphonuclear free radical generation after hypoxia-reoxygenation

Polymorphonuclear leukocytes (PMNLs), nitric oxide (NO), calcium, and free radicals play an important role in hypoxia/ischemia and reoxygenation injury. In the present study, NO donors, sodium nitroprusside (SNP), and diethylamine-NO (DEA-NO) at low concentrations (10 and 100 nmol/L) potentiated, while higher (10 micromol/L to 10 mmol/L) concentrations inhibited free radical generation response in the rat PMNLs. Free radical generation response was found to be significantly augmented when hypoxic PMNLs were reoxygenated (hypoxia-reoxygenation [H-R]). This increase in free radical generation after reoxygenation or SNP (10 nmol/L) was blocked in the absence of extracellular calcium. SNP (10 nmol/L) or H-R-mediated increases in the free radical generation were prevented by the pretreatment of PMNLs with NO scavenger (hemoglobin), the polyadenine diphosphate (ADP)-ribosylation synthase inhibitor (benzamide) or the calcium channel antagonist (felodipine). A significant augmentation in the nitrite and intracellular calcium levels was observed during hypoxia. Hemoglobin pretreatment also blocked the increase in intracellular calcium levels due to SNP (10 nmol/L) or hypoxia. Thus, increased availability of NO during SNP treatment or H-R, may have led to an ADP-ribosylation-mediated increase in intracellular calcium, thereby increasing the free radical generation from the rat PMNLs.

Wavelength selectivity of in-line fiber-optic filter devices

We present an analysis of the performance characteristics of in-line fiber-optic bandpass and band-stop wavelength filters. A planar waveguide model was used for numerical simulations of the device performance. It was recently reported that the band-stop and the bandpass characteristics of a filter device depend on the depth of polishing of a single-mode fiber. However, our numerical simulations show that both types of filter characteristic can be obtained with the same depth of polishing.

Hongoquercins, new antibacterial agents from the fungus LL-23G227: fermentation and biological activity

Two new antibiotics, hongoquercins A and B, were isolated from fermentation extracts of the unidentified fungus LL-23G227. In the optimum medium, titers of the A and B components reached approximately 2.1 g/liter and 0.02 g/liter, respectively. The optimum temperature for antibiotic production was approximately 22 degrees C. Growth was delayed at 15 degrees C but appeared to reach higher levels than was observed at 22 degrees C. Addition of dextrose to growth media increased hongoquercin B production. Hongoquercin A exhibited moderate activity against Gram-positive bacteria. Mechanistic studies conducted in an E. coli imp strain suggested membrane damage as the primary mode of bactericidal action. These compounds also lysed human red blood cells, suggesting a similar mode of action on eukaryotic cells.

Inhibition of platelet aggregation by a protein factor present in rat peripheral polymorphonuclear leukocyte supernatant

In the present investigation, effect of rat peripheral polymorphonuclear leukocyte (PMNL) supernatant was investigated on platelet aggregation. Rat PMNLs suspended in Hanks balanced salt solution (HBSS, pH 7.4) were incubated at 37 degrees C for different time intervals and cell-free supernatant was obtained by centrifugation. Supernatant was found to inhibit adenosine diphosphate (ADP), arachidonic acid (AA), and calcium ionophore-induced platelet aggregation. The inhibitory effect of PMNL supernatant on platelet aggregation was not blocked by methylene blue (10 microM) or adenosine deaminase (5 U ml(-1)) pretreatment, suggesting that the inhibitory effect of the supernatant on aggregation was not mediated by nitric oxide (NO) or ecto-ADPase. The effect of PMNL supernatant on platelet aggregation was abolished by preheating the supernatant at 95 degrees C for 5 minutes. Pretreatment of the supernatant with protease inhibitors abolished the inhibitory effect of supernatant on platelet aggregation suggesting that the factor may be a protein or peptide with protease activity. Partial purification of biologically active factor by fine particle liquid chromatography (FPLC) by using Superose 6B column yielded a peak with a molecular weight of approximately 30 kDa having antiaggregatory activity. The results obtained suggest that rat peripheral PMNLs release yet another factor(s) that inhibits platelet aggregation. The factor is a heat labile protein with a molecular weight of approximately 30 kDa.

Abdominal circumference in fetuses with congenital diaphragmatic hernia: correlation with hernia content and pregnancy outcome

To assess the value of abdominal circumference measurements in the second trimester as a predictor of mortality in fetuses with congenital diaphragmatic hernia, 34 fetuses with this condition who had had second trimester ultrasonographic evaluation were analyzed retrospectively for abdominal circumference measurements, content of the hernia, and pregnancy outcome. The abdominal circumference was below the fifth percentile in nine of the 27 fetuses (33%) with an isolated defect and in five of the seven fetuses (71%) with additional anomalies. In fetuses with isolated congenital diaphragmatic hernia, an abdominal circumference measurement below the fifth percentile was associated with the presence of the liver (P < 0.05) but not of the stomach in the chest. In 19 continuing pregnancies with an isolated defect, all five fetuses with an abdominal circumference below the fifth percentile either died prenatally (n = 1), soon after birth (n = 1), or after surgery (n = 3). In contrast, only six of the 14 fetuses (43%) with an abdominal circumference measurement within the normal range died, either soon after birth (n = 2) or after surgery (n = 4) (P < 0.05). We conclude that an abdominal circumference measurement below the fifth percentile in the second trimester appears to be a good predictor of a poor prognosis in fetuses with congenital diaphragmatic hernia.

SYN-1012: a new beta-lactamase inhibitor of penem skeleton

A new beta-lactamase inhibitor, SYN-1012, with a penem skeleton was synthesized and its biological activity compared with clavulanic acid, sulbactam, tazobactam and BRL-42715. The beta-lactamase inhibitory activity of SYN-1012 was comparable to BRL-42715. Clavulanate and penam sulphones (sulbactam and tazobactam) were more active against TEM-1 and OXA-1, but were less active against TEM-3 and cephalosporinase (Case) than SYN-1012. In combination with piperacillin, SYN-1012 exhibited comparable or slightly lower synergistic effects than BRL-42715 against all the Gram-positive and Gram-negative isolates tested with only exception of Pseudomonas aeruginosa. The separate combinations of SYN-1012 and BRL-42715 with ceftazidime and cefotaxime provided comparable results against Gram-negatives, but not against Gram-positive isolates. Tazobactam was inferior to SYN-1012 in all cases. In comparison to tazobactam, SYN-1012 and BRL-42715 were relatively unstable in human and mouse plasma, and in mouse liver and kidney homogenates. Serum level of SYN-1012 and BRL-42715 after an intravenous administration of 20 mg/kg in rabbit was undetectable after 1 hour.

The use of a dipstick antigen-capture assay for the diagnosis of Plasmodium falciparum infection in a remote forested area of central India

A study was carried out in a highly malarious forested belt of central India (Madhya Pradesh) to evaluate the usefulness of a dipstick antigen-capture assay (ParaSight F) as a diagnostic method for Plasmodium falciparum appropriate for field use. In all, 1,231 patients with fever were screened in parallel with the taking of thick blood smears. The sensitivity and specificity of the dipstick test for detection of P. falciparum were 93% and 92.5%, respectively. Results also indicate that the dipstick test result became negative within seven days after initiation of curative chemotherapy in the majority of cases (95%). Tribal populations in remote forested areas are important reservoirs of P. falciparum that are mostly resistant to standard antimalarial drugs and a source of malaria to the rest of the country. Control of malaria is limited by inaccessibility, lack of medical services, public ignorance of the disease, and other technical problems. In this population, the dipstick assay was found to be highly accurate, simple, and rapid, suggesting that it may be used in remote forested areas without the need for microscopic examination. The simplicity of the dipstick test enabled administration of more effective and expensive antimalarials preventing further buildup and dissemination of resistant parasites and a return of symptoms.

Magnitude of acute respiratory infections in under five children

A community based study was carried out in a rural area of Wardha district in Maharastra to measure the incidence of acute respiratory infections among children below 5 years age. 384 under five children were followed up fortnightly for one calendar year to estimate the incidence of acute respiratory infections (ARI). There were 1298 episodes of ARI averaging 3.67 episodes/child/year. The incidence of lower respiratory infections was 0.07 episodes/child/year. The incidence of ARI was found to be closely associated with nutritional status of the child, socio-economic status of the family, maternal literacy status and family size. Environmental factors like type of house, ventilation and fuel used for cooking were found to influence the incidence of ARI.

Early repair of inguinal hernia in preterm infants with oxygen-dependent bronchopulmonary dysplasia

Despite inguinal hernia being both common and problematic in a significant proportion of preterm infants with bronchopulmonary dysplasia (BPD), there has been a reluctance to intervene surgically for fear of exacerbating the underlying lung disease. We report our experience of early operation in 12 consecutive infants with varying degrees of oxygen-dependent BPD and investigate the effect of general anaesthesia and herniotomy on pulmonary function by measuring oxygen requirements prior to and following operation. Two infants who required oxygen in a concentration in excess of 95% failed to improve and died from the pulmonary disease 6 and 8 weeks following their operation. The remaining infants all showed a reduction in mean oxygen requirements in the weeks following operation. We conclude that, in the short term, hernia repair performed under general anaesthesia in infants with BPD of varying severity had no adverse effects on respiratory function, as determined by oxygen requirements. We suggest that in certain infants early repair may have been beneficial--potential mechanisms are explored.

Conformational characteristics of high affinity Sp1 binding enhancer elements of HIV-LTR by high resolution 2D-NMR

The understanding of early events in the expression of genes has vastly improved in recent years with the identification of a variety of gene- and sequence-specific DNA binding transcription factors. One such protein, Sp1, has been implicated in activating transcription of various cellular and viral genes including those of HIV, and SIV types of retroviruses. The basic recognition site for Sp1 has been identified as variants of a 10 base-pairs long GC-rich DNA, often containing a hexanucleotide segment 5'-GGGCGG (termed GC-box). However, variations in both the relative protein-DNA binding affinity and the nature of binding sequences have been noted. Two-dimensional 1H-NMR experiments (500 MHz) were employed for conformational studies of two decadeoxyribonucleotide duplexes, d(GAGGCGTGGC).d(GCCACGCCTC), termed Sp1-III, and d(GGGAGTGGCG).d(CGCCACTCCC), termed Sp1-I. These are two of the highest affinity Sp1 binding sites and consist of diverse positioning of the tri- and tetranucleotide segments GAG, GTG, GCG, GGCG, GTGG and GGAG, that occur frequently in other Sp1 binding sites as well, and may form specific contacts with the protein. Phase-sensitive nuclear Overhauser enhancement (2D-NOESY and MINSY) and correlation (COSY) spectra were obtained for the assignment of the exchangeable and nonexchangeable protons in a sequence-specific fashion. As a prelude to determination of the detailed solution structures of the selected sequences, numerous structural constraints were obtained from angle-dependent coupling constants and relative intensities of distance-dependent intra- and internucleotide NOEs. Overall, each duplex adopts a structure similar to B-DNA with predominantly C2'-endo/S-type sugar conformation and anti-glycosidic torsion angles. A selective disruption of sequential NOE connectivities at the GAG.CAC and GTG.CAC steps, irrespective of the flanking sequence, suggests that conformational changes at these sites may act as unique determinants of sequence specific recognition/binding of Sp1. Implications for a specific inhibition of Sp1-mediated transcription by minor groove binding class of drugs, designed to recognize GC-rich sequences, are also briefly discussed.