Advances in receptor-mediated resistance mechanisms of Lepidopteran insects to Bacillus thuringiensis toxin / 生物工程学报

Bacillus thuringiensis is widely used as an insecticide which is safe and environmentally friendly to humans and animals. One of the important insecticidal mechanisms is the binding of Bt toxins to specific toxin receptors in insect midgut and forming a toxin perforation which eventually leads to insect death. The resistance of target pests to Bt toxins is an important factor hampering the long-term effective cultivation of Bt crops and the continuous use of Bt toxins. This review summarizes the mechanism of insect resistance to Bt toxins from the perspective of important Bt toxin receptors in midgut cells of Lepidopteran insects, which may facilitate the in-depth study of Bt resistance mechanism and pest control.

Expression of cry1Ab gene from a novel Bacillus thuringiensis strain SY49-1 active on pest insects

ABSTRACT In this study, the cry1Ab gene of previously characterized and Lepidoptera-, Diptera-, and Coleoptera-active Bacillus thuringiensis SY49-1 strain was cloned, expressed and individually tested on Ephestia kuehniella (Lepidoptera: Pyralidae) and Plodia interpunctella (Lepidoptera: Pyralidae) larvae. pET-cry1Ab plasmids were constructed by ligating the cry1Ab into pET28a (+) expression vector. Constructed plasmids were transferred to an Escherichia coli BL21 (DE3) strain rendered competent with CaCl2. Isopropyl β-D-1-thiogalactopyranoside was used to induce the expression of cry1Ab in E. coli BL21(DE3), and consequently, ∼130 kDa of Cry1Ab was obtained. Bioassay results indicated that recombinant Cry1Ab at a dose of 1000 µg g-1 caused 40% and 64% mortality on P. interpunctella and E. kuehniella larvae, respectively. However, the mortality rates of Bt SY49-1 strains' spore-crystal mixture at the same dose were observed to be 70% on P. interpunctella and 90% on E. kuehniella larvae. The results indicated that cry1Ab may be considered as a good candidate in transgenic crop production and as an alternative biocontrol agent in controlling stored product moths.

Optimization of the RNeasy Mini Kit to obtain high-quality total RNA from sessile cells of Staphylococcus aureus

Biofilm formed by Staphylococcus aureus is considered an important virulence trait in the pathogenesis of infections associated with implantable medical devices. Gene expression analyses are important strategies for determining the mechanisms involved in production and regulation of biofilm. Obtaining intact RNA preparations is the first and most critical step for these studies. In this article, we describe an optimized protocol for obtaining total RNA from sessile cells of S. aureus using the RNeasy Mini Kit. This method essentially consists of a few steps, as follows: 1) addition of acetone-ethanol to sessile cells, 2) lysis with lysostaphin at 37°C/10 min, 3) vigorous mixing, 4) three cycles of freezing and thawing, and 5) purification of the lysate in the RNeasy column. This simple pre-kit procedure yields high-quality total RNA from planktonic and sessile cells of S. aureus.

Impact of brief exposure to antifungal agents on the post-antifungal effect and hemolysin activity of oral Candida albicans

AbstractPost-antifungal effect (PAFE) of Candida and its production of hemolysin are determinants of candidal pathogenicity. Candida albicans is the foremost aetiological agent of oral candidosis, which can be treated with polyene, azole, and echinocandin antifungals. However, once administered, the intraoral concentrations of these drugs tend to be subtherapeutic and transient due to the diluent effect of saliva and cleansing effect of the oral musculature. Hence, intra-orally, Candidamay undergo a brief exposure to antifungal drugs.Objective Therefore, the PAFE and hemolysin production of oral C. albicans isolates following brief exposure to sublethal concentrations of the foregoing antifungals were evaluated.Material and Methods A total of 50 C. albicans oral isolates obtained from smokers, diabetics, asthmatics using steroid inhalers, partial denture wearers and healthy individuals were exposed to sublethal concentrations of nystatin, amphotericin B, caspofungin, ketoconazole and fluconazole for 60 min. Thereafter, the drugs were removed and the PAFE and hemolysin production were determined by previously described turbidometric and plate assays, respectively.Results Nystatin, amphotericin B, caspofungin and ketoconazole induced mean PAFE (hours) of 2.2, 2.18, 2.2 and 0.62, respectively. Fluconazole failed to produce a PAFE. Hemolysin production of these isolates was suppressed with a percentage reduction of 12.27, 13.47, 13.33, 8.53 and 4.93 following exposure to nystatin, amphotericin B, caspofungin, ketoconazole and fluconazole, respectively.Conclusions Brief exposure to sublethal concentrations of antifungal drugs appears to exert an antifungal effect by interfering with the growth as well as hemolysin production of C. albicans.

Application of statistical experimental design for optimisation of bioinsecticides production by sporeless Bacillus thuringiensis strain on cheap medium

In order to overproduce bioinsecticides production by a sporeless Bacillus thuringiensis strain, an optimal composition of a cheap medium was defined using a response surface methodology. In a first step, a Plackett-Burman design used to evaluate the effects of eight medium components on delta-endotoxin production showed that starch, soya bean and sodium chloride exhibited significant effects on bioinsecticides production. In a second step, these parameters were selected for further optimisation by central composite design. The obtained results revealed that the optimum culture medium for delta-endotoxin production consists of 30 g L-1 starch, 30 g L-1 soya bean and 9g L-1 sodium chloride. When compared to the basal production medium, an improvement in delta-endotoxin production up to 50% was noted. Moreover, relative toxin yield of sporeless Bacillus thuringiensis S22 was improved markedly by using optimised cheap medium (148.5 mg delta-endotoxins per g starch) when compared to the yield obtained in the basal medium (94.46 mg delta-endotoxins per g starch). Therefore, the use of optimised culture cheap medium appeared to be a good alternative for a low cost production of sporeless Bacillus thuringiensis bioinsecticides at industrial scale which is of great importance in practical point of view.

Mecanismo de acción de la toxina alfa hemolisina de Escherichia coli / Action mechanism of Escherichia coli alpha-hemolysin toxin / Mecanismo de ação da toxina alfa-hemolisina de Escherichia coli

Escherichia coli es una de las bacterias anaerobias facultativas más predominantes en el intestino, siendo, en la mayoría de los casos, inocua para el huésped. Existen cepas que traslocan al torrente sanguíneo causando enfermedades extraintestinales como infecciones urinarias, septicemia y meningitis. Dentro de éstas se encuentran las cepas uropatogénicas (Uropathogenic Escherichia coli: UPEC), que secretan varios factores de virulencia. Estos últimos incluyen: toxinas, sistemas de adquisición de hierro, adhesinas y antígenos capsulares. Las principales toxinas secretadas son: alfa-hemolisina (HlyA) y el factor necrotizante citotóxico 1 (CNF-1). En esta revisión se presenta una descripción exhaustiva de HlyA, incluyendo su síntesis, maduración y exportación desde la bacteria. La acilación de la proteína en dos residuos internos de lisina la convierte en una toxina muy virulenta al exponer regiones intrínsecamente desordenadas que son esenciales en diferentes pasos del mecanismo de acción de la misma. Específicamente, la exposición de estas regiones está involucrada en interacciones proteína-proteína dentro del proceso de oligomerización. La formación del oligómero es responsable de la permeabilidad inducida en las células blanco. Finalmente, basado en los conocimientos acerca de las características estructurales y funcionales de HlyA, se presentan potenciales usos de HlyA en terapias basadas en toxinas.

Escherichia coli is one of the predominant species of facultative anaerobes in the human gut, and in the majority of the cases it is harmless to the host. Some strains of this species can translocate to blood and cause infection such as urinary infection, septicemia and meningitis. These are the uropathogenic E. coli strains (UPEC) that secrete a number of virulence factors. The latter include a number of secreted toxins, iron-acquisition systems, adhesins, and capsular antigens. Secreted toxins include HlyA, the cytotoxic necrotizing factor-1 (CNF-1). In this review an exhaustive description of the toxin has been delineated, including its synthesis, maturation, and export from the bacteria. The acylation of the protein at two internal lysine residues gives the toxin its virulence, by exposing intrinsic disordered regions that are essential in different steps of the toxin's mechanism of action. The further exposure of regions involved in the protein-protein interaction within the oligomerization process is responsG-ible for the permeability induced in all the target cells. Based on the already known structural and functional characteristics of HlyA, the potential use in toxin-based therapy is presented.

Escherichia coli é uma das bactérias anaérobias facultativas mais predominantes no intestino, sendo na maioria dos casos inócua para o hóspede. Há cepas que passam ao torrente sanguíneo causando doenças extraintestinais como infecção urinária, septicemia e meningite. Dentro destas se encontram as cepas uropatogênicas (Uropathogenic Escherichia coli: UPEC) que secretam varios fatores de virulência. Estos últimos incluem: toxinas, sistemas de aquisição de ferro, adesinas e antígenos capsulares. As principais toxinas secretadas são: alfa hemolisina (HlyA) e o fator necrotizante citotóxico 1 (CNF-1). Nesta revisão apresenta-se uma descrição exaustiva de HlyA incluindo sua sintese, seu amadurecimento e exportação a partir da bactéria. A acilação da proteína em dois residuos internos de lisina a transforma numa toxina muito virulenta ao expor regiões intrinsecamente desordenadas que são essenciais em diferentes passos do mecanismo de ação da mesma. Especificamente, a exposição destas regiões esta envolvida em interações proteína-proteína dentro do processo de oligomerização. A formação do oligômero é responsável pela permeabilidade induzida nas células alvo. Finalmente, com base nos conhecimentos acerca das características estruturais e funcionais de HlyA, apresentam-se potenciais usos de HlyA em terapias baseadas em toxinas.

The role of C-terminus carbohydrate-binding domain of Vibrio cholerae haemolysin/cytolysin in the conversion of the pre-pore β-barrel oligomer to a functional diffusion channel.

Background & objectives: Vibrio cholerae cytolysin/hemolysin (VCC) is a 65 kDa pore-forming toxin (PFT) secreted by O1 El Tor and non-O1 strains. The purified toxin, which contains two C-terminus carbohydrate-binding domains in addition to the cytolytic domain at the core, causes lysis of a wide spectrum of eukaryotic cells at picomolar concentrations, apoptogenesis of intestinal and immune cells and accumulation of fluid in rabbit ligated ileal loop. Therefore, it may potentially complement the action of cholera toxin (CT) in diarrheagenic strains that do not produce CT. We showed earlier that β1-galactosyl-terminated glycoconjugates are strong inhibitors of its pore-forming activity, though carbohydrates are not functional receptors of VCC. Here, we investigate how the 15 kDa C-terminus β-prism lectin domain contributed to pore formation in erthrocytes. Methods: VCC was isolated from the culture supernatant of late log phase grown bacteria and purified to homogeneity by chromatography. The 50 kDa truncated variant was generated by restricted proteolysis. Liposome was prepared by sonication of a suspension of phospholipids and calceine release assay was done by spectrofluorometric monitoring of the released dye trapped in liposome. Formation of β-barrel oligomers in erythrocyte stroma was monitored by scanning electron microscopy. Results: Proteolytic truncation of the C-terminus β-prism lectin domain decreased hemolytic activity of the toxin by ~800-fold without causing a significant change in pore-forming activity toward synthetic lipid vesicles devoid of incorporated glycoproteins/glycolipids. Truncation at the C-terminus did not impair membrane-binding or assembly to the oligomeric pore. Interpretation & conclusions: Our data indicated that the C-terminus domain played a critical role in translocation of the pre-pore oligomeric assembly from the cell surface or lipid-water interface to the hydrocarbon core of the membrane bilayer, signaling the formation of functional diffusion channels.

Verotoxic Escherichia coli (STEC) from beef and its products.

In the present investigation, out of 27 (24.10%) strains of Escherichia coli isolated from 112 beef samples comprising raw meat (45), kabab (36) and kofta (31), 9 (33.33%) belonging to 7 different serotypes were verotoxic as tested by vero cell cytotoxic assay. Serotype O145 was the predominant STEC in raw meat. Interestingly, one STEC-O157 strain was also detected. All the STEC strains were positive for Stx genes by polymerase chain reaction showing stx2 (77.78%) to be most predominant followed by stx1 (22.22%). Phenotypic enterohaemolysin production on washed sheep blood agar supplemented with CaCl2 revealed 6 (66.67%) STEC strains to be positive. Presence of STEC in cooked beef products, viz., kabab and kofta appeared to be a matter of concern and potential threat to public health.

Phenotypic characters of urinary isolates of Pseudomonas aeruginosa & their association with mouse renal colonization.

BACKGROUND & OBJECTIVE: Very few studies regarding production of virulence factors in different predominant serotypes of uropathogenic Pseudomonas aeruginosa are available and they have not been correlated to in vivo pathogenicity in the urinary tract. This study was carriedout with the objective to analyze the phenotypic characters of uroisolates of P. aeruginosa in vitro and to study the association of these virulence traits with their ability to cause nephropathogenicity in mouse model of ascending urinary tract infection (UTI). METHODS: Protease, elastase, alginate, haemolysin, pyochelin, pyoverdin and phopholipase C were measured using standard protocols in 18 uroisolates of P. aeruginosa isolated from patients suffering from complicated UTIs. An ascending model of pyelonephritis was established in Swiss Webster (LACA) female mice with these isolates. Quantitative bacterial count and histopathological evaluation of mouse renal tissue was done which were then assessed for a possible association with elaboration of virulence factors. RESULTS: All isolates of P. aeruginosa were able to colonize renal tissue of mice. However, renal counts varied amongst different isolates producing different virulence factors. Isolates producing high levels of haemolysin along with other virulence factors were able to colonize and multiply more in mouse renal tissue as compared to those producing low levels of haemolysin. INTERPRETATION & CONCLUSION: The findings of this study indicated an association between haemolysin production and renal colonization. High level of haemolysin production in vitro could be used as surrogate information for assessing pyelonephritic potential of P. aeruginosa.

Some virulence characteristics of uropathogenic Escherichia coli in different patient groups.

BACKGROUND & OBJECTIVE: Uropathogenic Escherichia coli have virulence properties, that are absent in non pathogenic E. coli. The distribution of these markers can vary according to patient populations. Hence, a study was undertaken to describe the presence of virulence factors like Pfimbriae, type 1 fimbriae and haemolysin in E.coli causing urinary infections in three groups of patients. Antibiogram was also recorded to determine differences, if any, between the groups. METHODS: E. coli isolated from three groups of subjects, in counts of >10(5) CFU/ml and in pure growth were tested for mannose resistant haemagglutination (MRHA) to indicate P fimbriae and mannose sensitive haemagglutination (MSHA) to indicate type 1 fimbriae. Haemolysin production and antimicrobial susceptibility patterns were also recorded. RESULTS: Significantly more isolates from antenatal and postnatal women possessed P fimbriae compared to groups with urologic abnormalities (P=0.05). Haemolysin production was also significantly higher (P<0.001) in this group. Greater proportions of isolates from pregnant women were susceptible to commonly used antimicrobials. However, resistance to third generation cephalosporins was present even in these isolates from community infections. INTERPRETATION & CONCLUSION: In patients with urological abnormality, E. coli with lower virulence can cause infections. Isolates from these patients exhibited greater drug resistance. In pregnant women and in community acquired infections, simple antimicrobial drugs like nitrofurantoin might still be useful. However, urgent and stringent policies for antimicrobial use and infection control in hospitals are required in India.

Haemolytic Escherichia coli in etiopathogenesis of pyelonephritis in rats--an experimental study.

Of the 26 urinary E. coli strains employed in the present study, 16 were haemolytic and 10 were non haemolytic in character. Of the 16 haemolytic strains injected through the exposed femoral vein of the rats, 12 showed the lesions of pyelitis, pyelonephritis and proliferation of glomerular tuft while 2 showed only the lesions of pyelitis and pyelonephritis. It was interesting to note that none of the nonhaemolytic strains produced any lesion in the animal. The data demonstrated a positive correlationship between haemolytic activity of E. coli and pyelonephritis in rats.

The effect of subminimal inhibitory concentrations of penicillin on growth rate and haemolysin activity of group G Streptococcus

The influence of the subminimal inhibitory concentrations (1/3 and 1/4 of the MIC) of penicillin on growth rate and on haemolysin production of a strain of group G Streptococcus was studied. It was shown that 1/3 of the MIC almost completely inhibited the bacterial growth, but it was not able to inhibit haemolysin activity in the culture supernate. The generation time of bacteria grown in 1/4 of the MIC was approximately twice longer than that of the control culture. In all cultures, the haemolysin, after being produced (or liberated), reached a peak and decreased to low levels, which could suggest that group G Streptococcus produces some end products of metabolism that are able to inhibit haemolysin activity

Hemolisinas bacterianas / Bacterial hemolysins

Hemolytic activity has been reported in bacteria of different genera. They were associated with a cytotoxic effect on erythrocytes by means of membrane damage which can results in a rearragement and disruption of the bilayer; in this case, they are considred cytilysins. They action mechanism of a hemilysins group is done by phospholipase activity on hydrophobic regions of membranes, this enzymatic action causes a pertubation that lyses erythrocytes of different animal species. The behavior of other bacterial hemolysins tends to resemble that detergents, bacause they have a very strong activity on surface, they have relatively low hemolytic effect and exhibit a broad spectrum of sensitive cells, without preference for a particularerythrocyte species. A third group of hemolysins encloses the lysins activated by SH compounds, sometimes called "oxygen-labile emolysins", they share common properties; all of them are irreversibly inactivated by low concentrations of cholesterol, the oxygen effect can be abolished by reducing agents, they are inmunologically related to one another and the temperature reduces their activity. The SF form of these lysins is active. -S-S-form obtained by oxydation us ubactuve abd does not interact with erythrocytes. Cholesterol represents the primary lysin acceptor of membrane, but there are some differences among the thiol-dependent cystolysins in: the reversibility of binding to membrane, the activity at -C and the damage caused in membranes with distinct leakage of cytoplasmic material ino the surrounding medium. The biggest group of hemolysins includes then lysins with an unknown mode of action, it comprises cytolysins of Gram-negative and Gram-positive bacteria. Althought the mechanisms of cell damage were studied by many investigators, the majority of hemolysins action mechanisms must be discovered. In the last years it was proposed that some bacterial lysins can act like other substances that pertub the membrane integrith by an important and very widespread mechanism of formation of transmembrane pores, with insertation of alien proteins into the lipid bilayer. When more hemolysins will be detected new characteistics and mode of actions will be more hemolysins will be detected new characteristics and mode of actions will be described, and the role if hemolysins in pathogeny will be best understood

Actividad hemolítica de Klebsiella pneumoniae sobre glóbulos rojos de conejo / Hemolytic activity of Klebsiella pneumoniae on rabbit erythrocytes

Se investigó la actividad hemolítica de Klebsiella pneumoniae, empleando cepas de referencia y cepas aisladas de infecciones. Todas las bacterias estudiadas resultaron hemolíticas en forma selectiva sobre eritrocitos de conejo. El frío intensificó el efecto lítico sobre los glóbulos rojos. Se estimó la capacidad hemolítica de las cepas mediante el diámetro de los halos producidos alrededor de orificios inoculados con 5 micron**l de suspensiones bacterianas. Cuando se realizó la detección de hemolisis en medios líquidos, sólo fue posible evidenciar lisis franca al tratar los cultivos con ciertos agentes reductores; de los cuales el más efectivo resultó el 2 mercaptoetanol. A la misma concentración los demás agentes químicos utilizados dieron menor porcentaje de eritrocitos lisados. La actividad hemolítica apareció en los cultivos durante la fase exponencial del crecimiento bacteriano y al cabo de 24 horas disminuyó al 33% del valor máximo alcanzado. Tanto la hemolisina cruda como la purificada reqirieron SH-activación y fueron inhibidas por suero