scholarly journals Participation of Valine 171 in α-Helix 5 of Bacillus thuringiensis Cry1Ab δ-Endotoxin in Translocation of Toxin into Lymantria dispar Midgut Membranes

2010 ◽  
Vol 76 (23) ◽  
pp. 7878-7880 ◽  
Author(s):  
Oscar Alzate ◽  
Cristina Osorio ◽  
Alvaro M. Florez ◽  
Donald H. Dean
Keyword(s):  
Bacillus Thuringiensis ◽  
Protein Stability ◽  
Manduca Sexta ◽  
Lymantria Dispar ◽  
Fold Increase ◽  
Mutant Protein ◽  
Specific Mechanism ◽  
Α Helix

ABSTRACT The Cry1Ab δ-endotoxin V171C mutant protein exhibits a 25-fold increase in toxicity against Lymantria dispar, which correlates with a faster rate of partitioning into the midgut membrane and slightly decreased protein stability. This is an insect-specific mechanism; similar results were not observed in Manduca sexta, another Cry1Ab δ-endotoxin-susceptible insect.

scholarly journals Gut Bacteria Are Not Required for the Insecticidal Activity of Bacillus thuringiensis toward the Tobacco Hornworm, Manduca sexta

2009 ◽  
Vol 75 (15) ◽  
pp. 5094-5099 ◽  
Author(s):  
Paul R. Johnston ◽  
Neil Crickmore
Keyword(s):  
Bacillus Thuringiensis ◽  
Manduca Sexta ◽  
Insecticidal Activity ◽  
Lymantria Dispar ◽  
Pieris Rapae ◽  
Galleria Mellonella ◽  
Sublethal Concentration ◽  
Gut Bacteria ◽  
First Instar ◽  
Vanessa Cardui

ABSTRACT It was recently proposed that gut bacteria are required for the insecticidal activity of the Bacillus thuringiensis-based insecticide, DiPel, toward the lepidopterans Manduca sexta, Pieris rapae, Vanessa cardui, and Lymantria dispar. Using a similar methodology, it was found that gut bacteria were not required for the toxicity of DiPel or Cry1Ac or for the synergism of an otherwise sublethal concentration of Cry1Ac toward M. sexta. The toxicities of DiPel and of B. thuringiensis HD73 Cry− spore/Cry1Ac synergism were attenuated by continuously exposing larvae to antibiotics before bioassays. Attenuation could be eliminated by exposing larvae to antibiotics only during the first instar without altering larval sterility. Prior antibiotic exposure did not attenuate Cry1Ac toxicity. The presence of enterococci in larval guts slowed mortality resulting from DiPel exposure and halved Cry1Ac toxicity but had little effect on B. thuringiensis HD73 Cry− spore/Cry1Ac synergism. B. thuringiensis Cry− cells killed larvae after intrahemocoelic inoculation of M. sexta, Galleria mellonella, and Spodoptera litura and grew rapidly in plasma from M. sexta, S. litura, and Tenebrio molitor. These findings suggest that gut bacteria are not required for B. thuringiensis insecticidal activity toward M. sexta but that B. thuringiensis lethality is reduced in larvae that are continuously exposed to antibiotics before bioassay.

scholarly journals 1186. Cefazolin inoculum effect predicts reduced susceptibility to other antibiotics and patient outcomes in MSSA endovascular infections

2020 ◽  
Vol 7 (Supplement_1) ◽  
pp. S617-S617
Author(s):  
Dan Smelter ◽  
Sue McCrone ◽  
Warren Rose
Keyword(s):  
Infective Endocarditis ◽  
Mortality Rate ◽  
Patient Outcomes ◽  
Treatment Options ◽  
Fold Increase ◽  
Specific Mechanism ◽  
Research Support ◽  
High Burden ◽  
Low Toxicity ◽  
Inoculum Effect

Abstract Background MSSA Infective endocarditis (IE) is inherently a high-burden infection with up to a 30% mortality rate. Cefazolin is an appealing treatment option for IE with low toxicity and a favorable dosing scheme. However, cefazolin has been associated with treatment failure in IE, attributed to an inoculum effect. The specific mechanism underlying the cefazolin inoculum effect (CIE) remains undetermined, but CIE has been linked to both blaZ expression and agr dysfunction. This study aims to determine whether CIE is linked to reduced susceptibility to other antibiotics and worse outcomes regardless of therapy in MSSA endovascular infections. Methods Sixty-four MSSA strains were collected from patients with endovascular infections not treated with cefazolin. To determine CIE phenotype, strains were cultured and MICs assayed for cefazolin, nafcillin, and vancomycin at 107 CFU/mL for high-inocula (HI) and 105 CFU/mL for standard-inocula (SI). This study defined CIE as a ≥ 4-fold increase in MIC at HI compared to SI, with at least an MIC of 4 mg/L at HI. Nitrocefin disks identified blaZ expression, and beta lysin disks were used to determine hemolysin type and agr function. Patient outcomes of mortality and bacteremia duration were assessed across cohorts. Results Twenty-four strains exhibit a CIE (38%), with 10 strains having an MIC of ≥ 32mg/L at HI. Nafcillin and vancomycin also had an inoculum effect, uncoupled from the CIE and occurring at a lower frequency and amplitude at HI. Presence of CIE had a greater association with blaZ expression (71% vs 25%) than agr dysfunction (38% vs 20%). 50% (9/18) of CIE infections were cleared within 48 hours while 77% (20/26) of CIE-negative infections were cleared within 48 hours (P=0.106). However, presence of CIE was not associated with increased mortality (25% CIE-positive vs 35%; P=0.578) Conclusion Previous studies for CIE failed to enrich for isolates from endovascular sources, where inocula are known to be high. This study presents one of the largest endovascular source cohorts for CIE evaluation. It identifies that CIE prevalence (38%) is higher than reports from diverse infection sources (10-36%). CIE appears to predict bacteremia duration with other MSSA treatment options, suggesting mechanisms independent of blaZ and agr function for this phenomenon. Disclosures Warren Rose, PharmD, MPH, Merck (Grant/Research Support)Paratek (Grant/Research Support)

scholarly journals Effects of Selection to Diflubenzuron and Bacillus thuringiensis Var. Israelensis on the Overwintering Successes of Aedes albopictus (Diptera: Culicidae)

Insects ◽  
2021 ◽  
Vol 12 (9) ◽  
pp. 822
Author(s):  
Charalampos S. Ioannou ◽  
Christos Hadjichristodoulou ◽  
Varvara A. Mouchtouri ◽  
Nikos T. Papadopoulos
Keyword(s):  
Bacillus Thuringiensis ◽  
Aedes Albopictus ◽  
Selection Process ◽  
Mosquito Species ◽  
Fold Increase ◽  
Development Of Resistance ◽  
Control Programmes ◽  
Invasive Mosquito ◽  
In The Wild ◽  
Successive Generations

Aedes albopictus is an invasive mosquito species responsible for local transmission of chikungunya and dengue viruses in Europe. In the absence of available treatments, insecticides-based control remains one of the most important viable strategies to prevent emerging problems. Diflubenzuron (DFB) and Bacillus thuringiensis var. israelensis (Bti) are among the most commonly used larvicides for Ae. albopictus control with consequent concerns for the potential development of resistance. Studies on the resistance emergence in Ae. albopictus and its persistence in the wild to both DFB and Bti are essential for the efficient and sustainable planning of the control programmes. In this context, larvae from a recently laboratory established population were subjected to increasing selective pressure for nine successive generations using both DFB and Bti. The resistance levels and the overwintering success of the selected populations relative to control (colonies that received no selection) were determined. Results revealed an 8.5- and 1.6-fold increase on the resistance levels following selection with DFB and Bti, respectively. The selection process to both larvicides had no apparent impacts on the overwintering capability relative to control, suggesting the successful persistence of the selected individuals in the wild on an annual base.

Changes in microvilli and Golgi-associated membranes of lepidopteran cells induced by an insecticidally active bacterial δ-endotoxin

1989 ◽  
Vol 93 (2) ◽  
pp. 337-347
Author(s):  
NANCY J. LANE ◽  
J. B. HARRISON ◽  
W. M. LEE
Keyword(s):  
Bacillus Thuringiensis ◽  
Gap Junctions ◽  
Manduca Sexta ◽  
Golgi Complex ◽  
Intramembranous Particle ◽  
Structural Alterations ◽  
Particle Population ◽  
Consistent Increase ◽  
Columnar Cells ◽  
Anterior Midgut

The δ-endotoxin from Bacillus thuringiensis var. kurstaki was fed to late larvae of the tobacco hornworm, Manduca sexta, to determine its effect on the anterior midgut epithelium, which was examined ultrastructurally at intervals thereafter. The cells of the midgut are primarily of the columnar and goblet variety and the effects of the toxin were more pronounced on the former. Tissues examined after only 1–5 min of exposure to the toxin already revealed fine-structural alterations. These were most notably changes in the microvilli and membranes associated spatially with the Golgi complex: vacuoles associated with its maturing face became enlarged. This effect was intensified with more-extensive exposure to the toxin, resulting in an increase in both vacuoles and the number of lysosomal bodies, many containing myelin-like formations; some of these arose as autophagic vacuoles. There seemed to be no consistent increase in endocytotic activity at the apical border, however. The intramembranous particle population of the microvilli of the columnar cells showed some slight changes with toxin treatment; alterations in microvillar contours also occured. The intercellular septate and gap junctions on the lateral borders were sometimes disrupted and with time often became internalized. It seems, then, that the toxin initially modifies the microvillar membranes and subsequently the Golgi-associated saccules are affected, giving rise to vacuoles and lysosomes.

Electron probe X-ray microanalysis of the effects of Bacillus thuringiensis var kurstaki crystal protein insecticide on ions in an electrogenic K+-transporting epithelium of the larval midgut in the lepidopteran, Manduca sexta, in vitro

1985 ◽  
Vol 74 (1) ◽  
pp. 137-152
Author(s):  
B.L. Gupta ◽  
J.A. Dow ◽  
T.A. Hall ◽  
W.R. Harvey
Keyword(s):  
Bacillus Thuringiensis ◽  
Manduca Sexta ◽  
Goblet Cell ◽  
Electron Probe ◽  
Apical Membrane ◽  
Short Circuit ◽  
Short Circuit Current ◽  
X Ray ◽  
Elemental Concentrations

An alkaline hydrolysate of Bacillus thuringiensis var kurstaki HD1 (Btk) parasporal crystals was administered at 25 micrograms ml-1 (f.c.) to isolated, short-circuited, midguts of tobacco hornworm (Manduca sexta) larvae. The short-circuit current (s.c.c.), a precise measure of K+ active transport, was inhibited by 78% in 10 min in Btk-treated midguts as compared to controls. The elemental concentrations of K, together with Na, Mg, P, S, Cl and Ca, as well as the water content, were determined by electron probe X-ray microanalysis (EPXMA) in the muscle cells, columnar cells and goblet cells, as well as in the extracellular goblet cavity and the bathing media. The average K concentration in the goblet cell cavity was 129 mmol/kg wet wt in control midguts but only 37 mmol/kg wet wt in Btk-treated midguts. The elemental concentrations, including that of K, in other cell compartments were much less affected by Btk, but a rise in total cell calcium is suggested. It has been previously suggested that in vitro Btk acts specifically on limited regions of the apical membrane of the midgut epithelial cells. The simplest interpretation of the EPXMA results would be that initially Btk interacts specifically with the goblet cell apical membrane, which bounds the goblet cavity and contains the K+ pump responsible for the s.c.c. and high transepithelial potential difference (p.d.). Such interaction results in a rapid disruption of K+ transport across the goblet cell apical membrane, leading to dissipation of the K+ gradient and loss of p.d. The histopathological changes previously reported by other workers would then be a consequence of K+ pump inhibition causing changes in the intracellular pH, Ca2+ etc. Some possible molecular bases for these specific interactions between Btk and cell membrane are discussed.

scholarly journals Pore-forming properties of the Bacillus thuringiensis toxin Cry9Ca in Manduca sexta brush border membrane vesicles

2010 ◽  
Vol 1798 (6) ◽  
pp. 1111-1118 ◽  
Author(s):  
Jean-Frédéric Brunet ◽  
Vincent Vachon ◽  
Marc Juteau ◽  
Jeroen Van Rie ◽  
Geneviève Larouche ◽  
...  
Keyword(s):  
Bacillus Thuringiensis ◽  
Manduca Sexta ◽  
Brush Border ◽  
Brush Border Membrane ◽  
Membrane Vesicles ◽  
Brush Border Membrane Vesicles ◽  
Bacillus Thuringiensis Toxin
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