Formulation of a flowable liquid concentrate of Bacillus thuringiensis serotype H-14 spores and crystals as mosquito larvicide

A.O. EJIOFOR AND N. OKAFOR. 1991. Bacillus thuringiensis serotype H-14 spores and crystals, produced in 5 1 fermenters, were centrifuged and resuspended in emulsified palm olein to give 3.2 × 10¹¹ colony forming units (cfu)/ml. The suspension was mixed with a cassava—molasses—palm olein—charcoal (CMPC-2) mixture which served as the carrier, adhesive, dispersant and protectant. The final concentration of the formulation was 3.2 × 10⁹ cfu/ml. The lethal concentrations capable of killing 50% of the test population (LC₅₀) of CMPC-2 during 0, 1 and 2 years of storage at 32 ± 4.C were 0.056, 0.058 and 0.058 mg/ml respectively as against 0.054, 0.051 and 0.054 mg/ml for the Institut Pasteur Standard—1978 (IPS-78) during the corresponding period. The² tests showed that the results were homogeneous at P = 0.05. The relative potencies of the preparation were 964.3, 879.3 and 931 International toxic units (ITU) Aedes aegypti as compared with the 1000 ITU assigned to IPS-78. At 95% confidence limits there was no significant difference between the potencies of CMPC-2 and IPS-78. Field tests showed that CMPC-2 provided between 87.5 and 100% control of natural populations of Aedes spp. and Cutex spp. Sedimentation tests showed that CMPC-2 settled markedly during storage. This, therefore, required that the product be thoroughly shaken before use.     

Immobilization in alginate as a technique for the preservation of Bacillus thuringiensis var. israelensis for long-term preservation

Technique for immobilization using sodium alginate as the matrix to preserve Bacillus thuringiensis var. israelensis isolates for long time storage was developed. Two strains of B. thuringiensis var. israelensis viz., VCRC B-17 and WHO standard strain IPS-82 were immobilized in alginate matrix and preserved at 4 degrees C and when tested both were found to have maintained excellent viability and mosquito larvicidal activity for 10 years. Mosquito larvicidal activity of B-17 and IPS-82 alginate beads, in term of LC(50) values before storage was 72.07 ng/ml and 47.07 ng/ml, respectively and after storage at 4 degrees C for a period of 1 to 10 years the values ranged from 69.88 to 73.86 ng/ml with a mean of 72.38 ng/ml and 45.32 to 48.60 ng/ml with a mean of 47.49 ng/ml, respectively. Similarly spore count of the beads of the respective strains was 4.37 x 10(8) and 3.33 x 10(10) CFU/mg before storage. After storage at 4 degrees C for a period of 1 to 10 years the counts of the beads of the respective strains ranged from 4.23 x 10(8) to 4.83 x 10(8) CFU/mg (mean of 4.49 x 10(8) CFU/mg) and 3.2 x 10(10) to 3.87 x 10(10) CFU/mg (mean of 3.54 x 10(10) CFU/mg). The alginate matrix immobilization technique has many advantages over free cells are that they enhance the stability of both spores and toxin against several physicochemical conditions and confer reduced susceptibility to contamination.     

Efficacy of Czechoslovak and Soviet Bacillus thuringiensis (serotype H-14) formulations against mosquito larvae

Laboratory and field comparisons were made with two wettable powder formulations of Bacillus thuringiensis serotype H-14 (B. t. H-14) prepared in Czechoslovakia ("Moskitur") and the USSR ("Baktokulicid"). Expressed in the international Aedes aegypti toxic units (TU X mg-1) the potency of these two test formulations was greater than that of the Institute Pasteur Standard IPS-78 (= 1,000 TU X mg-1), i.e. Moskitur had a potency of about 1,500 TU X mg-1 and the Soviet Baktokulicid 2,000 TU X mg-1. The Baktokulicid and Moskitur LC 90 values for laboratory-reared Aedes aegypti larvae were, respectively, 0.11 and 0.16 mg X l-1. The range of LC 90 values for the Czechoslovak wild-caught mosquito species of the genera Aedes and Culex was 0.14-0.31 mg X liter-1 with Moskitur, 0.11-0.41 mg X l-1 with Baktokulicid, and 0.16-0.48 mg X l-1 with IPS-78. The susceptibility of laboratory Anopheles stephensi larvae was close to that of Aedes aegypti, larvae of An. messeae required many times as much Baktokulicid (1.6 mg X l-1) and Moskitur (more than 6.4 mg X l-1) for 90% mortality as did other mosquito species. The aim of outdoor assays was to establish the minimum Moskitur and Baktokulicid rates giving a 100% control of mosquito larvae. For Ae. cantans breeding habitat in flood plain forest areas these rates ranged between 0.1-0.5 mg X l-1 (0.2-1.0 kg X ha-1), for Ae. vexans control on artificially irrigated meadows between 0.8-2.0 mg X l-1 (1.2-3.0 kg X ha-1). Consistently with laboratory bioassays, Baktokulicid gave 100% control of An. messeae 4th instar larvae at a dose as high as 3.2 mg X l-1, Moskitur gave 23.1% kill at 6.4 mg X l-1. The effect of Moskitur and Baktokulicid formulations was immediate, larvae that hatched 7-14 days posttreatment survived. The efficacy of B. t. H-14 outdoor treatments tended to markedly decrease with the larval densities exceeding 100 larvae per 1 dm2. Species of nontarget aquatic organisms, including the Diptera Chaoborus crystallinus, Mychlonyx sp. and Dixidae, were not noticeably affected by treatments with B. t. H-14 formulations used.     

A new black fly isolate of Bacillus thuringiensis autoagglutinating strain highly toxic to Simulium pertinax (Kollar) (Diptera, Simuliidae) larvae

Formulations containing the entomopathogenic Bacillus thuringiensis serovar israelensis strain IPS-82 has been widely applied for mosquito control around the world. Strain IPS-82 is highly active against Aedes aegypti but less active against other well-known vectors such as Culex quinquefasciatus and Simulium spp. larvae. Eighteen strains of B. thuringiensis were isolated from Simulium pertinax larvae naturally occurring in rivers of Southeast Brazil with one demonstrating special toxic effects. Simulated field tests against S. pertinax larvae showed that the native Brazilian autoagglutinating B. thuringiensis (LFB-FIOCRUZ 1035) has an LC50 at least 25 times lower than the standard IPS-82 strain. The same bacterial preparation was also tested against Ae. aegypti larvae in laboratory trials and the LC50 values obtained with LFB-FIOCRUZ 1035 were at least three times lower than the one for the IPS 82 strain. The results indicate that this strain is more toxic than the standard B. thuringiensis serovar israelensis (H14) in the two Dipteran species tested. It is noteworthy that differences between LC50 values were more pronounced in S. pertinax larvae, the source of the original isolation.     

Studies onBacillus thuringiensis H-14 strains isolated in Egypt—I. Screening for active strains

Screening for spore-forming bacteria to use against dipterous insects, namelyMusca domestica, Aedes aegypti andCulex pipiens from Egypt, led to two isolates, M1 and S128, being found which were highly toxic to bothAedes andCulex strains. They had calculated international Toxicity Units (ITU) valdes of 17,467 and 20,065 ITU/mg, respectively, as compared with 15,000 ITU/mg forBacillus thuringlensis H-14 IPS-82 Reference Standard. They were taxonomically classilled asBacllus thuringlensis H-14. Their sensitivity to a number ofBacillus phages is also described.

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Résumé Le criblage pour des bactéries sporulantes à utiliser contre des insecles diptères, notammentMusea domestica, Aedes aegypti, etCulex pipiens d'Egypte, a conduit à deux isolats, M1 et S128, dont on a montré la forte toxicité tant pour des souches deAedes que deCulex. Elles avaient des valeurs calculées d'Unités Internationales de Toxicité (UIT) respectivement de 17 467 et de 20 065 UIT par mg, ce qu'il faut comparer aux 15 000 UIT par mg chezBacillus thurigiensis H-14, standard de référence IPS-82. On les a classifiées sur le plan taxonomique commeBacillus thurigiensis H-14. On décrit également leur sensibillté à un certain nombre de phages deBacillus.

     

Susceptibility of zebra fish Danio rerio to infection by Flavobacterium columnare and F. johnsoniae

Flavobacterium columnare is a serious pathogen in a wide range of fish species. F. johnsoniae is an opportunistic pathogen of certain fish. Both are gliding bacteria. These species were tested for their ability to infect the zebra fish Danio rerio. Both injection and bath infection methods were tested. The results indicate that F. johnsoniae is not an effective pathogen in D. rerio, but that F. columnare is an effective pathogen. F. johnsoniae did not cause increased death rates following bath infection, but did cause increased death rates following injection, with an LD50 (mean lethal dose) of approximately 3 x 10(10) cfu (colony-forming units). Non-motile mutants of F. johnsoniae produced a similar LD50. F. columnare caused increased death rates following both injection and bath infections. There was considerable strain variation in LD50, with the most lethal strain tested producing an LD50 of 3.2 x 10(6) cfu injected and 1.1 x 10(6) cfu ml(-1) in bath experiments, including skin damage. The LD50 of F. columnare in zebra fish without skin damage was > 1 x 10(8), indicating an important effect of skin damage.     

Infection of barramundi Lates calcarifer with Streptococcus iniae: effects of different routes of exposure

The use of various challenge techniques has allowed the formation of a hypothesis for the mode of infection of Streptococcus iniae in barramundi. A bacterial dose of 1 x 10(3) colony forming units (cfu), corresponding to the LD50, delivered orally to barramundi could initiate the sub-acute form of the disease observed at the farms. The acute form of the disease could be initiated through bath exposure to the pathogen. S. iniae was equally as infective in freshwater, saltwater or when fish were subject to skin trauma prior to exposure, with LD50 values of 3.2 x 10(4), 2.0 x 10(4), 3.2 x 10(4) cfu, respectively, when observed over a 10 d period. It is suggested that sub-acute infection occurs orally, with mass mortalities occurring through the increased presence of the bacterium in the environment.     

Bifidobacterium longum ATCC 15707 cell production during free- and immobilized-cell cultures in MRS-whey permeate medium

Bifidobacterium longum ATCC 15707 cell production was studied in MRS medium supplemented with whey permeate (MRS-WP) during free-cell batch fermentations and continuous immobilized-cell cultures. Very high populations were measured after 12 h batch cultures in MRS-WP medium controlled at pH 5.5 (1.7+/-0.5x10(10) cfu/ml), approximately 2-fold higher than in non-supplemented MRS. Our study showed that WP is a low-cost source of lactose and other components that can be used to increase bifidobacteria cell production in MRS medium. Continuous fermentation in MRS-WP of B. longum immobilized in gellan gum gel beads produced the highest cell concentrations in the effluent (4.9+/-0.9x10(9) cfu/ml) at a dilution rate (D) of 0.5 h(-1). However, maximal volumetric productivity (6.9+/-0.4x10(9) cfu ml(-1)h(-1)) during continuous cultures was obtained at D =2.0 h(-1), and was approximately 9.5-fold higher than during free-cell batch cultures at an optimal pH of 5.5 (7.2x10(8) cfu ml(-1)h(-1)).     

Treatment of sanitary-important bacteria by bacteriocin substance V24 in cattle dung water

Quantification of sanitary-important bacteria (e.g. Enterobacteriaceae), as well as indicators of environmental contamination, was assessed in samples of cattle dung from 25 cattle farms in 15 north-eastern Slovakia districts. The inhibitory effect of crude bacteriocin extract CBE V24 from Enterococcus faecalis V24 against Listeria monocytogenes Ohio and Yersinia enterocolitica YE85 was examined in cattle dung water with the aim of finding a new way of eliminating the health risk of the animal slurry. The following bacterial groups were quantified: Salmonella spp., Shigella-like spp. , Proteus spp., Enterobacter spp., Citrobacter spp., Pseudomonas spp. , Escherichia coli, Listeria spp., staphylococci, streptococci and enterococci (the average count ranged from 102 up to 104 cfu ml-1). Antagonistic effect of the crude bacteriocin from Enterococcus faecalis V24 in the range of 100-600 Arbitrary units per ml (AU ml-1) was shown against the following bacteria: Enterobacter cloacae, Ent. asburiae, Proteus spp., Salmonella spp., Acinetobacter lwoffi, L. monocytogenes as well as Y. enterocolitica YE85. During tests performed to study the inhibitory effect of the crude bacteriocin CBE V24 (concentration 800, 1600 AU ml-1) against L. monocytogenes Ohio and Y. enterocolitica YE85 in experimentally contaminated cattle dung, a reduction of 2.03 and 1.44 log cfu ml-1, respectively, was already noted after 1 h after crude bacteriocin CBE V24 addition.     

Construction and characterization of a recombinant Bacillus thuringiensis subsp. israelensis strain that produces Cry11B

The mosquitocidal bacterium Bacillus thuringiensis subsp. israelensis (Bti) produces four major endotoxin proteins, Cry4A, Cry4B, Cry11A, and Cyt1A, and has toxicity in the range of many synthetic chemical insecticides. Cry11B, which occurs naturally in B. thuringiensis subsp. jegathesan, is a close relative of Cry11A, but is approximately 10-fold as toxic to Culex quinquefasciatus. To determine whether the addition of Cry11B to Bti would improve its toxicity, we produced this protein in Bti. High levels of Cry11B synthesis were obtained by expression of the cry11B gene under the control of cyt1A promoters and the STAB-SD sequence. This construct was cloned into the shuttle vector pHT3101, yielding the derivative plasmid pPFT11Bs, which was then transformed by electroporation into acrystalliferous (4Q7) and crystalliferous (IPS-82) strains of Bti. Synthesis of Cry11B in Bti 4Q7 produced crystals approximately 50% larger than those produced with its natural promoters without STAB-SD. However, less Cry11B was produced per unit culture medium with this construct than with the wild-type construct, apparently because the latter construct produced more cells per unit medium. Nevertheless, the Bti IPS-82 strain that produced Cry11B with pPFT11Bs was twice as toxic as the parental IPS-82 strain (LC(50) = 1.4 ng/ml versus 3.3 ng/ml, respectively) to fourth instars of C. quinquefasciatus. Against fourth instars of Aedes aegypti, no statistically significant difference between parental Bti IPS-82 (LC(50) = 4.7 ng/ml) and the Bti IPS-82 recombinant producing Cry11B (LC(50) = 3.5 ng/ml) was found in toxicity.     

Characterization of lactic acid bacteria isolated from the one humped camel milk produced in Morocco

One hundred and twenty (120) strains of lactic acid bacteria (LAB) were enumerated and isolated from raw dromedary milk in Morocco using various cultured media. Strains isolated were characterized by phenotypic, physiological and biochemical properties. Results showed that high counts of LAB were found. Presumptive lactobacilli counts ranged from 2.5x10(2) to 6x10(7)cfu/ml, presumptive lactococci levels varied from 5x10(2) to 6x10(7)cfu/ml, presumptive streptococci counts varied from 4.2x10(2) to 8x10(7)cfu/ml, presumptive leuconostoc levels ranged from 5.4x10(2) to 5.4x10(7)cfu/ml. Results showed also that Lactobacillus and Lactococcus were the predominant genera with 37.5% and 25.8%, respectively. The dominated species found were Lactococcus lactis subsp. lactis (17.5%), Lactobacillus helveticus (10%), Streptococcus salivarius subsp. thermophilus (9.20%), Lactobacillus casei subsp. casei (5.80%) and Lactobacillus plantarum (5%). This is the first report on the characterization of LAB strains isolated from the one humped camel milk produced in Morocco.     

Preparation of a flowable liquid bacterial insecticide based on Bacillus sphaericus

Fermenter-produced Bacillus sphaericus 2362 was formulated into a thick, dark flowable liquid concentrate containing 4.8×10⁹ c.f.u./ml and charcoal as protector against ultraviolet light. The potencies of the formulation against L₄ Culex pipiens quinquefasciatus before and after storage for 2 years were 5714 and 5862 International Toxic Units (ITU), respectively, when compared with a standardized B. sphaericus from the WHO at 1000 ITU. In field trials, treatment at 1.01/ha gave 96 to 100% control of mosquito larvae. B. sphaericus could be re-isolated in 5% of the samples 9 months after application.The authors are at the Department of Applied Microbiology & Brewing, Anambra State University of Technology, P.M.B. 5025, Awka, Nigeria.     

Efficacy of the biocontrol yeast Pichia anomala during long-term storage of moist feed grain under different oxygen and carbon dioxide regimens

The yeast Pichia anomala inhibits the spoilage mold Penicillium roqueforti in laboratory experiments with high-moisture wheat in malfunctioning airtight storage. The ability of P. anomala to prevent mold growth during 14 months of grain storage was evaluated in outdoor silos with different air permeabilities. Freshly harvested wheat in 160-kg portions was inoculated with 10(2) colony-forming units (cfu) g(-1) P. roqueforti, alone or together with 10(4) cfu g(-1) P. anomala. During the first month P. anomala increased to about 10(6) cfu g(-1) in the treated silos to reach 10(7) cfu g (-1) after 9 months. Naturally occurring P. anomala in the untreated silos increased from 10(2) to about 10(3) cfu g(-1) during the first month and reached the same level as the treated silos after 9 months. Oxygen levels were reduced below the detection limit within 1 day, while carbon dioxide levels increased to 80-90% during the first month. P. roqueforti did not grow in wheat treated with P. anomala, regardless of silo permeability, but had increased to 10(5) cfu g(-1) in the untreated silos after 14 months of storage.     

Isolation and characterization of heterotrophic,aerobic bacteria from oil storage caverns in northern Germany

Aerobic heterotrophic bacteria were enriched and isolated from three oil storage caverns of the German national oil reserve at different distances from the oil/brine interface. Microscopically no bacteria were found in the original samples, but colony counts showed more than 100 colony-forming units (cfu)/ml in two samples, whereas 0 to 4 cfu/ml were found in the other samples. Enrichments using defined mineral salts medium or complex medium revealed culturable organisms in all samples. All colony types were isolated and further separation of organisms during isolation was completed microscopically. Enrichments in media containing complex organic compounds led to higher numbers of isolates in samples near the oil/brine interface than enrichments with oil as the sole source of carbon. Micro-organisms that could utilize oil as the sole source of carbon were isolated from all enrichment cultures. Identification of the isolates revealedBacillus strains in all samples and coryneform bacteria in the samples from cavern 123.     

Efficacy of standard disinfectant test methods for contact lens-care solutions

Two disinfection systems based on hydrogen peroxide (0.5, 1.5 and 3%) and chlorhexidine gluconate (0.004%) were challenged in suspension tests using a modification of a standard method, with inocula containing 10⁶ or 10⁸ cfu/ml of the standard organisms Serratia marcescens, Pseudomonas aeruginosa and Staphylococcus warneri. The effect of an organic load on the shapes of microbial inactivation curves was also investigated. Although there were rapid declines in viability of 1–2 log units (cfu/ml) within the first minute of challenge in all cases, declines in viability subsequently levelled out rapidly, and with hydrogen peroxide viable counts increased slightly thereafter. These increases are unexplained, but may in part be attributable to disruption of cell clumps during challenge.     

Nutrient recovery from domestic wastewater using a UASB-duckweed ponds system

The pilot-scale wastewater treatment system used in this study comprised a 40-l UASB reactor (6-h HRT) followed by three duckweed ponds in series (total HRT 15 days). During the warm season, the treatment system achieved removal values of 93%, 96% and 91% for COD, BOD and TSS, respectively. Residual values of ammonia, TKN and total phosphorus were 0.41 mg N/l, 4.4 mg N/l and 1.11 mg P/l, with removal efficiencies of 98%, 85% and 78%, respectively. The system achieved 99.998% faecal coliform removal during the warm season with final effluent containing 4 x 10(3) cfu/100 ml. During the winter, the system was efficient in removing COD, BOD and TSS but not nutrients. The system was deficient in the removal of faecal coliforms during the winter, producing effluent with 4.7 x 10(5) cfu/100 ml. During the warm season, the N removal consisted of 80% by plant uptake, 5% by sedimentation and 15% unaccounted for. A duckweed production rate of 33 t dry matter per hectare per 8 months was achieved.     

Operational characteristics of an antibody-immobilized QCM system detecting Salmonella spp

A quartz crystal microbalance (QCM) system detecting Salmonella spp. was developed by an anti-Salmonella antibody immobilization onto one gold surface of a piezoelectric quartz crystal surface with sulfosuccinimidyl 6-[3-(2-pyridyldithio)propionamido]hexanoate (sulfo-LC-SPDP) thiolation. The optimum temperature and pH for the antibody-immobilized sensor were 35 degrees C and 7.2, respectively. The frequency shifts obtained were correlated with the Salmonella concentrations in the range 3.2 x 10(6)-4.8 x 10(8) CFU per ml. The system was quite specific to Salmonella spp. and applicable for repetitive use after a regeneration step employing 1.2 M NaOH. A model sample measurement was done for a market milk spiked with Salmonella typhimurium.     

Lipase activity in stallion seminal plasma and the effect of lipase on stallion spermatozoa during storage at 5 degrees C

Previous studies have demonstrated a detrimental effect of seminal plasma on the maintenance of motility of cooled equine spermatozoa; however, the mechanism for the adverse effect of seminal plasma during cooled storage remains undetermined. In goats, a glycoprotein component of bulbourethral gland secretion contains lipase activity that is detrimental to sperm motility when stored in skim milk-based extenders. The objective of the current study was to determine the amount of lipase activity in stallion seminal plasma and to determine the effect of added lipase on spermatozoal motility during cooled semen storage. In the first experiment, seminal plasma (1.0 ml) was assayed for lipase activity based upon hydrolysis of triglycerides (olive oil substrate) into free fatty acids and subsequent titration of pH change (SigmaDiagnostic Lipase Kit). Lipase activity in stallion seminal plasma was 0.36 +/- 0.02 Sigma units/ml, (mean + S.E.M.; n = 16 ejaculates from six stallions). In the second experiment, equine semen (three ejaculates from each of four stallions) was divided into five treatment aliquots. In Treatment 1, semen was extended 1:3 with nonfat dried skim milk extender (NFDSM). In treatment groups 2 through 5, spermatozoa were washed by centrifugation (300 x g for 15 min) and resuspended in NFDSM to a final concentration of 25 x 10(6) spermatozoa/ml. Porcine pancreatic lipase (pPL) was added to Treatment 3 (10 pPL units/ml), Treatment 4 (100 pPL units/ml) and Treatment 5 (100 pPL units/ml, heat inactivated at 100 degrees C for 5 min) while Treatment 2 had no pancreatic lipase added and served as the control. Samples were cooled slowly to 5 degrees C, and stored at 5 degrees C until evaluation. Sperm motility was evaluated at time 0, 24, 48 and 72 h by computerized semen analysis, and data were analyzed via repeated measures ANOVA. The addition of 100 units/ml but not 10 units/ml of pPL decreased (P < 0.01) total and progressive motility of stored sperm. Heat-inactivated pPL (Treatment 5) did not significantly decrease motility of spermatozoa during storage. Because the lipase activity assayed (Sigma units) and the lipase activity added to cooled semen (pPL units) were not equivalent, pPL was assayed in the Sigma Diagnostic Lipase assay. The relationship between Sigma Units (Y) and pPL units (X) appeared to be a log-linear relationship with log(Y) = -0.912 + 0.007X; R2 = 0.90. Mean lipase activity assayed in stallion seminal plasma was equivalent to approximately 64 pPL units/ml. These data suggest that endogenous lipase activity in stallion seminal plasma may be a factor in the adverse effects of seminal plasma on cooled spermatozoa in some stallions.     

Survival of Brucella abortus strain RB51 lyophilized and as liquid vaccine under different storage conditions.

Brucella abortus strain RB51 (SRB51) is a new cattle vaccine that is approved for use in the U.S. for prevention of brucellosis. At the present time, other countries are implementing or considering the use of SRB51 vaccine in their brucellosis control programs. In the current study, the effect of three stabilizing media, two fill volumes (1 and 3 ml), and three storage temperatures (-25, 4 and 25 degrees C) on the viability of lyophilized SRB51 over a 52 week period was determined. The effects of three concentrations of bacteria (5 x 10(8), 1 x 10(9), or 5 x 10(9) cfu/ml) and two storage temperatures (4 or 25 degrees C) on viability of liquid SRB51 vaccine were also determined. For lyophilized strain RB51 vaccine, fill volume did not influence viability (P> 0.05) during lyophilization. Although fill volume did not influence viability during storage in World Health Organization (WHO) media or media containing both WHO and Lactose Salt (LS) media, 1 ml fill volumes of SRB51 in LS media had greater (P< 0.05) viability when compared to 3 ml fill volumes. Lyophilized SRB51 vaccine stored at 25 degrees C had a more rapid decline in viability (P< 0.05) when compared to vaccine stored at -25 or 4 degrees C. With the exception of the 3-ml fill volumes of LS media, all three stabilizing media were similar in maintaining viability of SRB51 at -25 degrees C storage temperatures. However, when compared to WHO or WHO/LS media, stabilization in LS media was associated with a more rapid decline in viability during storage at 4 or 25 degrees C (P< 0.05). Initial SRB51 concentration in liquid vaccine did not influence (P> 0.05) viability during storage at 4 or 25 degrees C. When compared to liquid SRB51 vaccine stored at 25 degrees C, storage at 4 degrees C was associated with a slower decline in viability (P< 0.05) during 12 weeks of storage. Biochemical and morphological characteristics of SRB51 were stable under the storage conditions utilized in the present study. This study suggests that viability of SRB51 can be readily maintained during storage as a lyophilized or liquid brucellosis vaccine.     

Rapid and sensitive magnetoelastic biosensors for the detection of Salmonella typhimurium in a mixed microbial population

In this article, we report the results of an investigation into the performance of a wireless, magnetoelastic biosensor designed to selectively detect Salmonella typhimurium in a mixed microbial population. The Langmuir-Blodgett (LB) monolayer technique was employed for antibody (specific to Salmonella sp.) immobilization on rectangular shaped strip magnetoelastic sensors (2 x 0.4 x 0.015 mm). Bacterial binding to the antibody on the sensor surface changes the resonance parameters, and these changes were quantified as a shift in the sensor's resonance frequency. Response of the sensors to increasing concentrations (5 x 10(1) to 5 x 10(8) cfu/ml) of S. typhimurium in a mixture of extraneous foodborne pathogens (Escherichia coli O157:H7 and Listeria monocytogenes) was studied. A detection limit of 5 x 10(3) cfu/ml and a sensitivity of 139 Hz/decade were observed for the 2 x 0.4 x 0.015 mm sensors. Binding kinetics studies have shown that the dissociation constant (K(d)) and the binding valencies for water samples spiked with S. typhimurium was 435 cfu/ml and 2.33 respectively. The presence of extraneous microorganisms in the mixture did not produce an appreciable change in the biosensor's dose response behavior.