Broth Suspension Research Articles

Production and Evaluation of Antibodies and Phage Display-Derived Peptide Ligands for Immunomagnetic Separation of Mycobacterium bovis

This study describes the development and optimization of an immunomagnetic separation (IMS) method to isolate Mycobacterium bovis cells from lymph node tissues. Gamma-irradiated whole M. bovis AF2122/97 cells and ethanol-extracted surface antigens of such cells were used to produce M. bovis-specific polyclonal and monoclonal antibodies in rabbits and mice. They were also used to generate M. bovis-specific peptide ligands by phage display biopanning. The various antibodies and peptide ligands obtained were used to coat MyOne tosyl-activated Dynabeads (Life Technologies), singly or in combination, and evaluated for IMS. Initially, M. bovis capture from Middlebrook 7H9 broth suspensions (concentration range, 10 to 10(5) CFU/ml) was evaluated by IMS combined with an M. bovis-specific touchdown PCR. IMS-PCR results and, subsequently, IMS-culture results indicated that the beads with greatest immunocapture capability for M. bovis in broth were those coated simultaneously with a monoclonal antibody and a biotinylated 12-mer peptide. These dually coated beads exhibited minimal capture (mean of 0.36% recovery) of 12 other Mycobacterium spp. occasionally encountered in veterinary tuberculosis (TB) diagnostic laboratories. When the optimized IMS method was applied to various M. bovis-spiked lymph node matrices, it demonstrated excellent detection sensitivities (50% limits of detection of 3.16 and 57.7 CFU/ml of lymph node tissue homogenate for IMS-PCR and IMS-culture, respectively). The optimized IMS method therefore has the potential to improve isolation of M. bovis from lymph nodes and hence the diagnosis of bovine tuberculosis.

TiO2and N-Doped TiO2Induced Photocatalytic Inactivation ofStaphylococcus aureusunder 405 nm LED Blue Light Irradiation

Irradiation source has been a serious impediment to induce photocatalytic bacterial inactivation which was taken as an advanced indoor air purification technique. Here we reported the synergistic effects of 405 nm LED light and TiO2photocatalyst in inactivation process ofStaphylococcus aureus(S. aureus). In this work, TiO2and N-doped TiO2particles were, respectively, suspended into the nutrient broth suspension withS. aureus. Then, the mixed system was exposed to a 405 nm LED light source with energy density of about 0.2 W/cm2for 3 hours. Irradiated suspension was then scanned by UV-vis spectrophotometer for bacteria survive/death rate statistics. Subsequently, the inactivation efficiency was calculated based on the difference of the absorption optical density between experimental and controlled suspensions. Results showed that both TiO2and N-doped TiO2particles exhibit potential bacterial inactivation effects under similar experimental conditions. Specifically, N-doped TiO2with the concentration of 5 g/L displayed enhanced inactivation efficiency againstS. aureusunder 405 nm LED light irradiation. Thus, it is a promising indoor air purification technique by using N-doped TiO2particles under the LED light irradiation.

Effect of Low Dose γ-Irradiation on the Fate and Cell Envelope of Bacillus cereus, Escherichia coli, and Salmonella Typhimurium

This study investigated the effect of low dose <TEX>${\gamma}$</TEX>-irradiation on the damage of the cell envelopes and antibiotic sensitivity profiles of Bacillus cereus, Escherichia coli, and Salmonella Typhimurium. The bacteria suspension in tryptic soy broth was exposed to the <TEX>${\gamma}$</TEX>-irradiation doses of 0, 1, 1.5, 3, and 5 kGy, and then stored at <TEX>$0^{\circ}C$</TEX> for 24 h. A viability test, an antimicrobial sensitivity profile, and an electron microscopy were performed to observe the effects due to <TEX>${\gamma}$</TEX>-irradiation treatment. B. cereus could survive the <TEX>${\gamma}$</TEX>-irradiation up to 5 kGy while E. coli and S. Typhimurium were all deactivated at 1.5 kGy and 5 kGy, respectively. At 5 kGy, the cell count of B. cereus was significantly reduced, and the survived bacteria cells retained their important features. There were no significant changes observed in the antimicrobial sensitivity profile (p>0.05) for the recovered bacteria after irradiation treatment. Low dose <TEX>${\gamma}$</TEX>-irradiation below 3 kGy was found to be insufficient to achieve decontamination of B. cereus and S. Typhimurium. Cell envelope damage and deactivation of different bacteria did not occur in the same manner; thus, deferent doses of <TEX>${\gamma}$</TEX>-irradiation may be required for deactivation of different bacteria.

Bacterial translocation across ePTFE vascular graft surfaces

Vascular graft infections arise from bacterial colonization of either the external or internal graft surfaces. We assessed whether methicillin-resistant Staphylococcus aureus (MRSA) and Escherichia coli could translocate through pores of ePTFE grafts. To assess translocation from the internal to the external surface, we placed 10(5) cfu of bacterial suspension inside ePTFE graft segments and suspended them in sterile broth for 72 h. To assess translocation from the external to the internal surface, we placed sterile broth inside ePTFE segments, and incubated them for 72 h in a bacterial suspension (10(5) cfu/mL). At 72 h, in addition to culturing the sterile broth and bacterial suspensions, the external and internal surfaces were first qualitatively cultured separately and then quantitatively cultured by sonication. At 72 h, the sterile broth remained sterile. The bacterial suspensions yielded 10(7)-10(9) cfu/mL. Graft cultures indicated that colonization of one surface with either organism did not result in bacterial translocation to the other surface. Quantitative bacterial counts of the external vs. internal surfaces were significantly different (p < 0.01). MRSA and E. coli do not translocate across ePTFE graft surfaces. These in-vitro findings help elucidate the pathogenesis of graft infections and prompt conduction of validation studies in-vivo.

Effect of the enrichment time and immunomagnetic separation on the detection of Shiga toxin-producing Escherichia coli O26, O103, O111, O145 and sorbitol positive O157 from artificially inoculated cattle faeces

The purpose of this study was to evaluate the effect of enrichment time and immunomagnetic separation (IMS) on the efficiency of a method to isolate non-O157 Shiga toxin-producing Escherichia coli (STEC) serotypes O26, O103, O111, O145 and sorbitol positive (s+) O157 from artificially inoculated cattle faeces. Cattle faecal samples were inoculated with varying amounts (20–90 cfu/25 g and 200–900 cfu/25 g) of clinical STEC strains (including serotypes O26, O103, O111, O145 and O157 (s− and s+)), and recovered using a selective enrichment step of either 6 or 24 h, followed by plating on selective agars either preceded by IMS or not. Two types of IMS beads were used (Dynabeads ® and Captivate™ beads), and evaluated on pure broth suspensions of STEC. The 6-h enrichment instead of 24-h, had no significant effect on the recovery rate, only for serotype O145 a positive trend was observed. Using direct plating after enrichment, recovery rates were influenced by the inoculated serotype and the inoculation level. Using IMS (Dynabeads ® or Captivate™ beads), recovery of serotype O157 (s− and s+) was significantly improved, whereas for O26, O103, O111, and O145 no significant effect was observed. Results of IMS performed on pure suspensions of STEC, explained these serotype-depended findings in faeces; loss-making factors in the IMS procedure of some beads and the influence of the type of bead were shown. The method combining both enrichment periods with direct plating and IMS followed by plating, yielded a detection limit of 20–90 cfu/25 g. But, if only certain serotypes have to be investigated, the protocol can be simplified.

Microfungal Alkylation and Volatilization of Selenium Adsorbed by Goethite

Selenium adsorbed in the oxyanionic form by Fe-oxides like goethite is considered of benefit for long-term stabilization of (79)Se under near field conditions of radionuclide waste disposal sites. However, microbe-mediated volatilization of the uranium fission product (79)Se has not yet been considered for risk assessment based on the use of the water-solid distribution coefficient K(D). We have performed incubation experiments in a ternary system selenium-microbe-goethite and show that mycobiota including the common black microfungi genera Alternaria alternata are capable of volatilizing the Se even if immobilized by goethite. The microfungi were incubated in a standardized nutrient broth suspension with 10 g L(-1) of the oxide target under defined conditions. Volatile organic selenium (VOSe) species formed in the head space of the culture flasks were sampled and measured directly by a cryotrapping cryofocusing gas chromatographic system coupled with ICP-MS detection (CT-CF-GC-ICP-MS). Alkylated VOSe species were found at the tens to hundreds ng m(-3) levels dominated by dimethyl selenide (DMSe) and dimethyl diselenide (DMDSe). The total amount of DMSe released into the 80-mL headspace volume within the 21 days of incubation was up to 1.12 +/- 0.17 nmol and 0.48 +/- 0.12 nmol for systems without and with goethite amendment, respectively. Alkylation rates of up to 0.1 mumol Se per day and g biomass cannot be neglected as a potential fission product mobilization pathway, unless the inherent radioactivity is proven to prevent any such microbial activity on the long-term. Otherwise it may lead to an onsite accumulation of (79)Se through evapoconcentration in the enclosed underground caverns.

Inactivation of Listeria innocua in tryptic soy broth and poultry meat samples by high pressure processing

Efficiency of high-pressure processing (HP) on the inactivation of Listeria innocua (ATTC 33090) suspensions in culture medium or inoculated into poultry samples was studied. First, the baroresistance of L. innocua in a tryptic soy broth suspension at a concentration of 108–109 Colony forming units (CFU)/ml was tested under varying cycles of pressurization in the range of 200–350 MPa (15 min total in each treatment) at 4 °C. In addition, the effect of HP on L. innocua inoculated in poultry (103 or 105/CFU/g) was examined. The results of these studies demonstrate the requisite treatment conditions and efficacy of pressure cycles in destroying L. innocua in poultry.

Pseudomonas viridiflava Causing Necrotic Leaf Spots and Defoliation on Hebe spp. in Northern Spain.

Hebe spp. is gaining interest as an ornamental crop in Spain. In October of 2003, plants of Hebe spp. (cv. Pink Paradise, Recurva, and Topiaria) grown in a nursery located in a northern region of Spain (Principality of Asturias) developed dark reddish spots in leaves. The spots (favored by high-humidity conditions) appeared initially in internal and lower leaves, but eventually progressed to the rest of the plant causing extensive defoliation. Samples from symptomatic leaves were processed for microbiological analysis. From the samples, Stemphylium sp. and fluorescent Pseudomonas sp., identified by conventional microbiological methods (1,3), were consistently recovered. Two isolates of the fungi and two of the bacterium (LPPA 365 and LPPA 366) were used in artificial inoculations of healthy plants (cv. New Zeeland) and all were performed in duplicate. A Stemphylium sp. was inoculated by irrigation of four seedlings with a suspension obtained by homogenization of the mycelium collected from two plates of potato dextrose agar in 100 ml of sterile distilled water. An equal number of seedlings were sprayed with a bacterial suspension (108 CFU/ml) in yeast extract peptone glucose broth. The same methods were used to inoculate all four combinations of fungi and bacteria. The seedlings were maintained at 22°C during 1 month with a 16/8-h photo-period, but in inoculations with bacteria they were initially kept under transparent plastic bags for 48 h to facilitate entry. Seedlings treated with sterile distilled water were included as controls. Although a powdery film of sooty mold was observed in some of the leaves irrigated with one of the two Stemphylium sp. strains, rusty lesions and defoliation did not occur on plants inoculated with the fungal isolates alone. In contrast, symptoms comparable with those observed in the field developed in plants inoculated with the bacteria, either alone or together with the fungus. Reisolation of fluorescent Pseudomonas sp. from symptomatic leaves taken from inoculated plants confirmed pathogenicity on Hebe spp. The pathogenic isolates were tentatively identified as atypical Pseudomonas viridiflava on the basis of biochemical tests (2,3), and their identity was then confirmed by sequencing of the gene encoding the 16S rRNA (3; GenBank Accession Nos. AM182933 and AM182934 for LPPA 365 and 366, respectively). To our knowledge, this is the first report of P. viridiflava as the cause of necrotic leaf spots and defoliation in Hebe spp.

Antibiotic Susceptibility Tests Directly on Urine Samples Using Uro-Quick, A Rapid Automated System

During the period June 2003-March 2004, 12,579 urine samples were examined employing the Uro-Quick system. Positive samples (1,948) were subsequently Gram-stained and processed by standard procedures for microorganism identification and antibiotic susceptibility determination by the disk diffusion method. Results of this latter test were compared with those obtained employing the new rapid Uro-Quick method. Antibiotics were introduced in vials containing 2 ml of Mueller-Hinton broth, then 0.5 ml of urine or a bacterial suspension in broth were added; a vial without drug was used as control. After 3 and 5 hours of incubation (for Gram-negative and Gram-positive strains respectively) the instrument showed the results. No growth and a growth curve like the control indicated susceptible and resistant strains respectively. Overall 1,590 Gram-negative strains were tested against ciprofloxacin, nitrofurantoin, amoxicillin-clavulanate, ceftazidime, fosfomycin, imipenem, amikacin, trimethoprim-sulfamethoxazole, and piperacillin-tazobactam, while 358 Gram-positive bacteria were assessed against ciprofloxacin, nitrofurantoin, amoxicillin-clavulanate, ampicillin, fosfomycin, gentamicin, oxacillin and trimethoprim-sulfamethoxazole. Against the major urinary tract pathogens (Escherichia. coli, enterococci, Klebsiella spp. and Proteus spp.) agreement between the Uro-Quick system and the disk diffusion test generally was >90% for all antibiotics tested. On the basis of these results the system appears useful not only for bacteriuria screening, but also to rapidly test the antibiotic susceptibility of common uropathogens.

Inactivation of Staphylococcus aureus and Salmonella enteritidis in tryptic soy broth and caviar samples by high pressure processing

We studied the action of high pressure processing on the inactivation of two foodborne pathogens, Staphylococcus aureus ATCC 6538 and Salmonella enteritidis ATCC 13076, suspended in a culture medium and inoculated into caviar samples. The baroresistance of the two pathogens in a tryptic soy broth suspension at a concentration of 10(8)-10(9) colony-forming units/ml was tested for continuous and cycled pressurization in the 150- to 550-MPa range and for 15-min treatments at room temperature. The increase of cycle number permitted the reduction of the pressure level able to totally inactivate both microorganisms in the tryptic soy broth suspension, whereas the effect of different procedure times on complete inactivation of the microorganisms inoculated into caviar was similar.

Investigation of the impact of simulated commercial centrifugation and microfiltration conditions on levels of Mycobacterium avium ssp. paratuberculosis in milk

The potential for physical removal of Mycobacterium avium ssp. paratuberculosis (M. paratuberculosis) from milk by centrifugation and microfiltration was investigated by simulating commercial processing conditions in the laboratory by means of a microcentrifuge and syringe filters, respectively. Results indicated that both centrifugation of preheated milk (60°C) at 7000 × g for 10 s, and microfiltration through a filter of pore size 1.2 µm, were capable of removing up to 95–99.9% of M. paratuberculosis cells from spiked whole milk and Middlebrook 7H9 broth suspensions, respectively. Centrifugation and microfiltration may therefore have potential application within the dairy industry as pretreatments to reduce M. paratuberculosis contamination of raw milk.

An in vitro Study on the Active Conversion of Flucytosine to Fluorouracil by Microorganisms in the Human Intestinal Microflora

Background: Investigation of the rate of active conversion of flucytosine to fluorouracil by microorganisms in the intestinal microflora. Methods: Active conversion of flucytosine was investigated using viable and nonviable Escherichia coli at different flucytosine concentrations. Additionally, flucytosine conversion was studied in fecal specimens from 3 neutropenic patients at the start of the antimicrobial/antifungal prophylaxis (C/A regimen) and 1 week later. Results: Flucytosine levels decreased by an average of 72, 71 and 72% flucytosine after incubation for 48 h of 10¹⁰ viable E. coli/ml suspension in broth containing 13, 130 and 1,300 mg/l flucytosine, respectively. The decreasing flucytosine levels corresponded approximately to an identical increase in fluorouracil levels. Also, a 44% decrease of flucytosine levels occurred when nonviable E. coli were used, indicating that bacterial viability is not necessary for this conversion. When fecal specimens of 2 patients were investigated prior to the C/A regimen, significant flucytosine conversion occurred, whereas this conversion was not observed in the corresponding fecal specimens after 1 week of C/A regimen. Conclusion: These in vitro experiments showed that extensive flucytosine conversion can occur in the human intestinal microflora by E. coli. Consequently, fluorouracil exposure and fluorouracil-related toxicity may occur in the flucytosine-treated patient.

Application-dependent, laboratory-based validation of an enzyme-linked immunosorbent assay for Aeromonas salmonicida

A heterologous, noncompetitive, sandwich, enzyme-linked immunosorbent assay (ELISA) has been developed for the detection of Aeromonas salmonicida. This paper reports the initial, laboratory validation of the applications of this assay to the study of the ecology of A. salmonicida in the effluents of freshwater hatcheries, marine sediments and in fish. The selectivity of the assay was investigated by the use of four (one core and three application-dependent) control panels of bacteria. No false-negative and two false-positive reactions were detected in the core panel that contained 108 strains of the target species, 100 strains of nontarget mesophilic aeromonads and 19 miscellaneous strains. The two false-positive reactions were generated by strains of Staphylococcus aureus. In the 74-strain panel for application to fish tissues and the 150 strain panel for freshwater sediment applications, no false positives were detected. Two false positives were, however, detected in the 150-strain panel for applications to marine sediments. Nine samples of environmental matrices, which the proposed applications of this assay might require to be examined, were used in an investigation of performance characteristics of the assay in spiked and unspiked matrices. The matrices exerted a slight influence of the baseline values generated by the assay and reduced the intra- and interassay precision; however, in all cases, these changes were within acceptable limits. The applied lower detection limits for A. salmonicida in spiked environmental matrices were in the range 1–4×10 3 cfu/ml and were slightly higher than the limits detected in broth suspensions of the organism. The ELISA was also demonstrated to have the ability to detect A. salmonicida in studies of incurred freshwater and sediments. The laboratory experiments reported here failed to detect any evidence that would argue against the initiation of full-scale validation studies of this method under field conditions.

Sensitivity of Two Disjunct Bacterioplankton Communities to Exudates from the Cyanobacterium Microcystis aeruginosa Kützing.

Microcystis aeruginosa Kützing releases a variety of bioactive compounds during growth. This study determined whether bacteria from communities co-occurring (M+) or not (M-) with this cosmopolitan cyanobacterium respond similarly to its products. Fifty M+ bacteria from a M. aeruginosa bloom site (Western Basin of Lake Erie) and 50 M- bacteria from a Microcystis-free site (East Twin Lake, Portage Co., OH) were isolated and grown on Standard Methods Agar. Three levels of testing were performed: chemotaxis, antibiotic response, and 48-h cell abundance. Chemotaxis was compared using capillary tubes placed in contact with bacterial, Standard Methods Broth (SMB) suspensions. The capillary choices were conditioned SMB, M. aeruginosa exudate, and BG-11. M+ bacteria showed significantly greater (Tukey's test, p < 0.005) positive chemotaxis to M. aeruginosa exudate compared to control conditions and to M-strains. The latter showed a negative chemotactic response to M. aeruginosa exudate compared to control conditions. Antibiotic response was tested by sensitivity disk assays, first using M. aeruginosa exudates, whole cells, and homogenized cells, and then placing the disks on bacterial lawns of each strain. M+ bacteria were significantly more resistant to inhibition than M- bacteria (chi-square test, p < 0.01). M. aeruginosa exudate, BG-11 algal medium, SMB, and distilled water effects on 48-h abundance of the strains were compared. The M- community bacteria exhibited significantly lower growth yields (Tukey's comparison of means test, p < 0.005) in M. aeruginosa exudate than did the M+ strains. It is evident that those bacteria co-occurring with M. aeruginosa are more likely to be attracted to it, able to withstand exposure to it, and able to utilize its products without inhibition than are bacteria from communities without previous exposure to this cyanobacterium.

The risk of nosocomial pneumonia is not increased during partial liquid ventilation.

To determine whether partial liquid ventilation (PLV) affects the risk of nosocomial pneumonia. To assess in vitro bacterial adhesion and viability after liquid perfluorocarbon exposure and to assess bacterial recovery after partial liquid ventilation in vivo in rabbits. University animal research facility. Thirty-six New Zealand White rabbits. To assess adhesions, radiolabeled Escherichia coli were exposed to perfluorocarbon, incubated against artificial biosurfaces, and compared with nonexposed controls. Bacterial viability in vitro was assessed by exposing broth suspensions of Pasteurella multocida to perflubron for various times. Controls were run in parallel without exposure. Quantitative cultures were performed to determine viability. We undertook short-term and recovery in vivo investigations. The lungs of treated animals were filled with perflubron (approximately 18 mL/kg), and the control rabbits were ventilated without perflubron in an identical fashion. Cryopreserved aliquots of P. multocida were administered via an endotracheal tube. The short-term study animals were ventilated for 6 hrs before being killed. The recovery animals were ventilated for 2-4 hrs, extubated, and killed 20 hrs later. The lungs were removed, aseptically minced, and homogenized. Serial dilutions of the homogenate were quantitatively cultured by manual counting of colonies on agar plates. The recovered organisms were typed for species by the clinical microbiology laboratory. The adhesion of bacteria to immobilized bronchoalveolar lavage and human saliva, respectively, was reduced by 65%+/-7% and 66%+/-1% (p < .05; n = 5) after exposure to perflubron and by 63%+/-9% and 68%+/-6% after exposure to FC-77 (p < .05; n = 5); however, adhesion was not affected by exposure to Rimar. There was no difference in bacterial viability between the control and perflubron-exposed bacteria (n = 5). The in vivo study demonstrated a ten-fold or greater reduction in the number of recovered bacteria in the partial liquid ventilated group compared with the control group. This study suggests that different perfluorocarbons affect adhesions differently. Perflubron and FC-77 appear to decrease bacterial adhesion, whereas Rimar does not. Rerflubron does not have a direct bactericidal effect. Furthermore, PLV with perflubron decreased the number of viable bacteria per gram of tissue after an intentional inoculation of the airway, suggesting that the risk of nosocomial pneumonia is unlikely to be increased during PLV and may, in fact, be reduced in patients supported with PLV.

ラピブロットＥｓｃｈｅｒｉｃｉａ ｃｏｌｉ Ｏ１５７（栄研）の評価

Rapiblot E. coli O157 is based on the use of anti-E. coli O157 antibody-coated Polymacron, as a high-surface-area immunoadsorbent for rapid capture and subsequent immunoenzyme detection of E. coli O157 antigens extracted from test samples by heating at 100°C for 10 minutes.Atotal of 24 non-E. coli O157 strains and various gram-negative and gram-positive bacteria tested gave negative results.The detection limit of Rapiblot E. coli O157 was 105cfu/ml in assays of E. coli O157 strains in broth suspension prepared by the spread plate method.This highly specific and sensitive selective antibody procedure was 98% effective when tested against IMS using ground beef and radish sprouts.The results obtained by Rapiblot E. coli O157 were the same or better than those of other commercial kits to detect E. coli O157.Rapiblot E. coli O157 was therefore considered effective for the detection of E. coliO157 in food.

Aspects of the use of complex media for submerged fermentation of Aspergillus awamori

For the industrial production of enzymes using fungi, often complex media containing solid substrates are used. In this study, fermentations with Aspergillus awamori were performed using wheat bran. The results are compared with previous work on synthetic medium. Major differences are that the wheat bran was not consumed completely as glucose or sucrose and that fungi growing on the wheat bran particles (adhesion growth) may occur depending on the inocula used. If the spore concentration was higher than 1.3 × 10 5 spores ml −1, adhesion growth dominated. If the concentration was lower than 1.8 × 10 4 spores ml −1, wheat bran free pellets and clean wheat bran particles dominated. In between these two values, the broth suspension consisted of wheat bran free pellets, clean wheat bran particles, and adhesion colonies. Solid substrate suppressed the growth in free filamentous mycelial form. A method was developed to separate the wheat bran particles from the pellets. The kinetics with complex medium appeared to be essentially the same as with synthetic medium. The ratio of biomass production to the sum of biomass production and CO 2 production was a function of time and independent of operation conditions, morphology, and substrates (sucrose, glucose, or wheat bran). Gas-liquid mass transfer coefficients during the fermentations were determined and compared with a correlation from the literature.

Rheological, Mass Transfer, and Mixing Characterization of Cellulase-Producing Trichoderma reesei Suspensions

Steady and dynamic shear measurements are utilized to characterize the rheological behavior of Trichoderma reesei RUT-C30 fungal suspensions during batch growth on xylose (soluble substrate) or cellulose (particulate solid substrate) at three different fermentor impeller speeds (250, 400, and 550 rpm). Biomass concentrations versus time were unimodal on xylose and bimodal on cellulose. This behavior is consistent with relatively rapid, early growth on easily metabolized growth medium components (yeast extract), followed by a second, slower growth phase due to hydrolysis of recalcitrant cellulose by increasing cellulase concentrations. Critical dissolved oxygen (DO) concentration for T. reesei growth on cellulose was found to be 0.073 mmol/L. The DO was kept above this level by supplementing the air feed with pure oxygen, implying that mass transfer limitations were not the cause of bimodal cell growth. Steady shear rheological data showed shear thinning behavior and a yield stress for all broth samples regardless of substrate. Casson and Herschel−Bulkley constitutive equations fit steady shear data well. Dynamic shear measurements on broth suspensions indicated “gel-like” behavior at low strains, with microstructural breakdown at larger displacements. Time variations of the Casson model parameters (yield stress and Casson viscosity) and dynamic moduli (elastic and viscous modulus) followed both cell mass and morphology: a single maximum in all rheological variables resulted when cells were grown on xylose or on cellulose at impeller speeds of 400 or 550 rpm, and dual maxima were observed for cellulose-grown cells at 250 rpm.

Comparison of the inhibitory and lethal effects of synthetic versions of plant metabolites (anethole, carvacrol, eugenol, and thymol) on a food spoilage yeast(Debaromyces hansenii)

Abstract The inhibitory and lethal effects of synthetic versions of compounds found in common herbs and spices were compared on a food spoilage yeast Debaromyces hansenii. Separate treatments of trans‐anethole, carvacrol, eugenol, and thymol were investigated in potato dextrose broth (PDB) suspension cultures. Inhibitory activity was studied for all compounds at concentrations of 25, 50, 75, and 100 ppm over a 55 h incubation while lethality was investigated for trans‐anethole, carvacrol, and thymol at 100 and 125 ppm over a four day incubation. All compounds exhibited at least minor inhibitory activity at a concentration of 25 ppm. During the 55 h incubation period, the minimum concentration for total inhibition by trans‐anethole was 75 ppm, while that for carvacrol and thymol was 100 ppm. The maximum level of eugenol examined, 100 ppm, did not completely inhibit outgrowth. Growth curve data were described by the logistic equation which provided for quantitative comparison of inhibition. Lethality was achieved with trans‐anethole, carvacrol, and thymol at 100 and 125 ppm as determined by colony forming units (CFU) on potato dextrose agar (PDA) over four days incubation. These findings demonstrate an approach for quantitatively describing inhibition and evaluating the lethal effects of synthetic versions of plant metabolites on D. hansenii. This research may prove useful in future studies identifying active compounds, determining their effective concentrations, and providing strategies for the development of food applications.

Microfiltration of yeast suspensions with self‐cleaning spiral vortices: Possibilities for a new membrane module design

A novel method of producing controlled vortices was used to reduce both concentration polarization and membrane fouling during microfiltration of Saccharomyces cerevisiae broth suspensions. The method involves flow around a curved channel at a sufficient rate so as to produce centrifugal instabilities (called Dean vortices). These vortices depolarize the build-up of suspended particles such as yeast cells at the membrane-solution interface and allow for increased membrane permeation rates. Various operating conditions under which such vortices effectively reduced cake build-up of suspended particles such as yeast cells at the membrane-solution interface and allow for increased membrane permeation rates. Various operating conditions under which such vortices effectively reduced cake build-up during microfiltration of 0 to 0.55 dry wt% yeast broth were investigated. Flux improvements of over 60% for 0.25 dry wt% yeast broth for flow with over that without Dean vortices were observed. This beneficial effect increased with increasing retentate flow rate and increasing transmembrane pressure and decreased with increasing concentration of suspended matter. Similar behavior was observed whether the cells were viable of killed. the improvement in flux in the presence over that in the absence of vortices correlated well with centrifugal force or azimuthal velocity squared. The relative cake resistances increased with reservoir yeast concentration. These values with vortices increased from 62% to 75% of that without vortices with increasing yeast concentration. The ratio of the cake thicknesses in the limiting case (at high feed concentration) was 3.25. These results suggest that self-cleaning spiral vortices could be effective in maintaining good and steady microfiltration performance with cell suspensions other than those tested.