Effect of Relative Humidity on the Survival of Airborne Unicellular Algae

A method is described which is suitable for assessing the effects of relative humidity (RH) on the viability of two unicellular algae in experimental aerosols. Viable cells of Nannochloris atomus collected from the airborne state were detected by plating onto agar surfaces of an appropriate growth medium, whereas viable airborne cells of Synechococcus sp., because of unreliable growth on solid media, were determined by a liquid assay system. The assays were performed at intervals during short-term and prolonged storage of algal aerosols in chambers preconditioned to a selected RH and temperature. Both species showed the greatest loss in viability during the first minute after atomization, and the extent of this inactivation, as a function of RH, reflected the subsequent long-term survival. The airborne eukaryotic alga was unable to survive at an RH below 91%, whereas the airborne prokaryotic alga was comparatively stable over a wide humidity range. Initial inactivation was least and long-term survival best, for both species, at 94% RH.     

Efficacy of iodine-treated biocidal filter media against bacterial spore aerosols

Aims: To assess the effectiveness of iodine-treated biocidal filter media against bacterial spore aerosols. Methods and Results: Bacillus subtilis spores were aerosolized and introduced into a filtration system. Both treated and untreated filters exhibited high viable removal efficiency (>99·996%) with negligible variation in pressure drop during the entire experiment. The viability of collected spores on the filter was investigated by enumeration of spores extracted from the filter by vortexing. At room temperature and low relative humidity (RH), the survival fraction of the treated filter was significantly lower than that of the untreated filter (P-value < 0·05). Meanwhile, at room temperature and high RH and at high temperature and high RH, the survival fractions on the treated medium were statistically the same as the untreated control at room temperature and low RH. Conclusions: Both treated and untreated filters achieved excellent viable removal efficiency for spores. The pressure drop of the treated filter was not affected by the iodine treatment. The viability of collected bacterial spores was decreased because of the exertion of iodine disinfectant. Significance and Impact of the Study: The evaluation demonstrates that the iodine-treated filter is a viable medium for respiratory protection against infectious spore aerosols. The results warrant further evaluation of smaller biological agents, which exhibit higher penetration.     

Inactivation of Baceriophage T3 in Aerosols: Effect of Prehumidification on Survival After Spraying from Solutions of Salt, Peptone, and Saliva

Coliphage T₃ was inactivated by a factor of 10³ to 10⁴ within 30 min after spraying from solutions of NaCl. Addition of peptone to the spray medium protected against inactivation at high relative humidity (RH), presumably by preventing surface inactivation. Prehumidification of the sample before collection had no effect on recovery if sprayed from solutions of NaCl, with or without peptone. If only peptone was present in the spray medium, prehumidification of the aerosol sample increased the recovery by a factor of 1,000 at low RH and by a factor of 5 at high RH. In aerosols sprayed from saliva, inactivation was nearly equal to that in peptone, with an increase of recovery after prehumidification by a factor of 1,000.     

Reaction of Airborne Rhizobium meliloti to Some Environmental Factors

Survival of Rhizobium meliloti 102F5 in aerosols at 20 C was maximal at high relative humidity (RH) and minimal at low RH. Relatively high concentrations of NO(2), SO(2), or formaldehyde were needed to significantly reduce viability of R. meliloti in aerosols at 50% RH. Except for the reduction in activity of formaldehyde by SO(2), there was no additive or antagonistic effect of mixing pollutants. High environmental RH enhanced bactericidal activity of NO(2) and SO(2). High RH minimized and low RH accentuated the biological effect of ultraviolet light of 300 to 400 nm wavelength.     

Survival of Campylobacter jejuni inoculated into ground beef.

Ground beef was inoculated with mixed cultures of Campylobacter jejuni, and the samples were subjected to various cooking and cold-storage temperatures. When samples were heated in an oven at either 190 or 218 degrees C, approximately 10(7) cells of C. jejuni per g were inactivated (less than 30 cells per g) in less than 10 min after the ground beef reached an internal temperature of 70 degrees C. When the samples were held at -15 degrees C over 14 days of storage, the numbers of C. jejuni declined by 3 log10. When inoculated samples were stored with an equal amount of Cary-Blair diluent at 4 degrees C, no changes in viability were observed over 14 days of storage. Twenty-five times as much C. jejuni was recovered from inoculated ground beef when either 10% glycerol or 10% dimethyl sulfoxide was added to an equal amount of ground beef before freezing as was recovered from peptone-diluted ground beef. Twice as much inoculated C. jejuni was recovered from ground beef plus Cary-Blair diluent as was recovered from ground beef plus peptone diluent.     

Influence of temperature and humidity on the survival of Monilinia fructicola conidia on stone fruits and inert surfaces

The survival of the fungus Monilinia fructicola on fruit and inert surfaces at different temperatures (range: 0–30°C) and relative humidity (RH) (range: 60–100%) was investigated. M. fructicola conidia survived better on fruit than on inert surfaces. The viability reduction rate at 20°C and 60% RH was 1.2 and 5.8 days^?1 on fruit and inert surfaces, respectively. Overall, on fruit surfaces, conidia viability was reduced at high temperatures and was longer at higher RH than at lower RH; in contrast, on inert surfaces, conidia viability was longer at only low temperatures. On fruit surfaces, at 0°C and 100% RH, conidia survived up to 35 days, and at 30°C and 60% RH, conidia survived up to 7 days. However, on inert surfaces at 20°C and 30°C, conidia lost their viability after 48 and 24 h, respectively. These results suggest that M. fructicola can remain viable in cold rooms for over 30 days on fruit surfaces or over 25 days on inert surfaces. Furthermore, under the orchard conditions during the growing season, conidia may remain viable for only 2–3 days on immature fruit surfaces before conidia will be unable to penetrate the host.     

Airborne Stability of Tailless Bacterial Viruses S-13 and MS-2

The effect of relative humidity (RH) on the airborne stability of two small bacterial viruses, S-13 and MS-2, was studied. Poorest recovery of S-13 was obtained at 50% RH. Humidification prior to aerosol sampling significantly increased the recovery of S-13 at RH deleterious to the airborne virus. A commercial preparation of MS-2 suspended in a buffered saline solution showed a rapid loss of viability at RH above 30%, whereas a laboratory preparation containing 1.3% tryptone showed high recoveries at all RH studied. Dilution of the commercial MS-2 into tryptone broth conferred stability on the airborne virus. Humidification prior to sampling significantly reduced the viable recovery from aerosols of commercial MS-2, whereas the laboratory preparation was unaffected.     

Airborne Stability of Simian Virus 40

The influence of relative humidity on the airborne survival of simian virus 40 (SV40) was studied by allowing virus aerosols to age in rotating drums at 21 or 32 C and at a relative humidity (RH) value ranging from 22 to 88%. Airborne SV40 virus was stable at every RH tested at 21 C, but aerosols maintained at 32 C were inactivated within 60 min at mid-range RH values. The unusual stability at 21 C over a broad RH range indicates that potentially biohazardous situations may occur under laboratory conditions if this virus becomes accidentally airborne.     

Inactivation of Mycobacterium paratuberculosis by pulsed electric fields

The influence of treatment temperature and pulsed electric fields (PEF) on the viability of Mycobacterium paratuberculosis cells suspended in 0.1% (wt/vol) peptone water and in sterilized cow's milk was assessed by direct viable counts and by transmission electron microscopy (TEM). PEF treatment at 50 degrees C (2,500 pulses at 30 kV/cm) reduced the level of viable M. paratuberculosis cells by approximately 5.3 and 5.9 log(10) CFU/ml in 0.1% peptone water and in cow's milk, respectively, while PEF treatment of M. paratuberculosis at lower temperatures resulted in less lethality. Heating alone at 50 degrees C for 25 min or at 72 degrees C for 25 s (extended high-temperature, short-time pasteurization) resulted in reductions of M. paratuberculosis of approximately 0.01 and 2.4 log(10) CFU/ml, respectively. TEM studies revealed that exposure to PEF treatment resulted in substantial damage at the cellular level to M. paratuberculosis.     

Influence of Temperature and Relative Humidity on Germinability of Mucor piriformis Spores

Studies were conducted to determine the influence of temperature and relative humidity (RH) on germinability and viability of Mucor piriformis spores. Spores did not survive when stored at 35 °C and their survival rate decreased rapidly at 30 °C; however, spores remained viable for more than 1 year at 0 °C. RH also significantly affected spore viability. Spores held at 26 °C and 100% RH no longer germinated after 35 days, while those held at 75 or 90% RH germinated for 65 days. At 20 °C, RH had little effect on spore germinability. The effect of temperature and RH on percentage spore germination also varied. At all temperatures studied, spore viability decreased more rapidly with time at 100% RH than at 75 or 90% RH. The least favorable, temperature-humidity combination, 30 °C and 100% RH, decreased spore germination from 100% to less than 1% in 14 days.     

Influence of water activity and temperature on survival of and colony formation by heat-stressed Chrysosporium farinicola aleuriospores.

The ability of sublethally heat-stressed aleuriospores of Chrysosporium farinicola to form colonies on yeast extract-glucose agar (YGA) supplemented with sufficient glucose, sorbitol, glycerol, and NaCl to achieve reduced water activity (aw) in the range of 0.88 to 0.95 was determined. The effects of the aw of diluent and incubation temperature during recovery and colony formation were also investigated. Aleuriospores harvested from 14-day-old cultures grown at 25 degrees C were less resistant to heat inactivation compared with aleuriospores from 20-day-cultures. Increased populations of heat-stressed aleuriospores were recovered as the aw of YGA was decreased from 0.95 (glucose and glycerol) and 0.94 (sorbitol) to 0.89 and 0.88, respectively. In NaCl-supplemented YGA, populations recovered at an aw of 0.94 were greatly reduced compared with populations detected at an aw of 0.92; no colonies were formed on NaCl-supplemented YGA at an aw of 0.88. Tolerance to aw values above 0.88 to 0.89 as influenced by solute type was in the order of glucose greater than sorbitol greater than glycerol greater than NaCl. Incubation at 20 degrees generally resulted in an increase in recoverable aleuriospores compared with incubation at 25 degrees C or at 30 degrees C for 14 days followed by 20 degrees C for 10 days. The lethal effect of NaCl on heat-stressed aleuriospores was enhanced at 30 degrees C. The retention of viability of aleuriospores held in sucrose-peptone water diluent (aw, 0.936) for 20 min was essentially the same as that observed when aleuriospores were held in peptone water (aw, 0.997).(ABSTRACT TRUNCATED AT 250 WORDS)     

Observations on the survival and infectivity of airborne rinderpest virus

The most frequent means of spread of rinderpest, a cause of major epizootics and of great economic losses among cattle in the tropics, remains undetermined. Studies on airborne virus in vitro demonstrated survival for at least 30 min at low RH and a somewhat inferior period of survival at high RH; viability was greatly reduced at 50–60% RH. The infectivity of 3 strains of airborne rinderpest virus for cattle was demonstrated by a technique employing direct inhalation of viral aerosols.     

Influence of water activity and temperature on survival of and colony formation by heat-stressed Chrysosporium farinicola aleuriospores

The ability of sublethally heat-stressed aleuriospores of Chrysosporium farinicola to form colonies on yeast extract-glucose agar (YGA) supplemented with sufficient glucose, sorbitol, glycerol, and NaCl to achieve reduced water activity (aw) in the range of 0.88 to 0.95 was determined. The effects of the aw of diluent and incubation temperature during recovery and colony formation were also investigated. Aleuriospores harvested from 14-day-old cultures grown at 25 degrees C were less resistant to heat inactivation compared with aleuriospores from 20-day-cultures. Increased populations of heat-stressed aleuriospores were recovered as the aw of YGA was decreased from 0.95 (glucose and glycerol) and 0.94 (sorbitol) to 0.89 and 0.88, respectively. In NaCl-supplemented YGA, populations recovered at an aw of 0.94 were greatly reduced compared with populations detected at an aw of 0.92; no colonies were formed on NaCl-supplemented YGA at an aw of 0.88. Tolerance to aw values above 0.88 to 0.89 as influenced by solute type was in the order of glucose greater than sorbitol greater than glycerol greater than NaCl. Incubation at 20 degrees generally resulted in an increase in recoverable aleuriospores compared with incubation at 25 degrees C or at 30 degrees C for 14 days followed by 20 degrees C for 10 days. The lethal effect of NaCl on heat-stressed aleuriospores was enhanced at 30 degrees C. The retention of viability of aleuriospores held in sucrose-peptone water diluent (aw, 0.936) for 20 min was essentially the same as that observed when aleuriospores were held in peptone water (aw, 0.997).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of Simulated Solar Radiation and Sodium Fluorescein on the Recovery of Venezuelan Equine Encephalomyelitis Virus from Aerosols

Almost 90% of the Trinidad strain of Venezuelan equine encephalomyelitis (VEE) virus survived for 1 hr after aerosolization into a dark environment at 30% relative humidity (RH), and 78% survived for 1 hr at 60% RH. After exposure to simulated solar radiation (584 mcal per cm(2) per min) 0.02% of the aerosolized virus survived for 1 hr at 30% RH and 0.006% survived for 1 hr at 60% RH. When 1.0 mg of sodium fluorescein per ml was added to suspensions prior to aerosol dissemination (to determine physical loss of aerosol), no virus was detected after 30 min at either RH upon irradiation. Sodium fluorescein also exhibited some toxicity (31% survival at 60 min) for nonirradiated aerosols of VEE virus at 60% RH; no effect was noted at 30%.     

Influence of temperature and relative humidity on the survival of Chlamydia pneumoniae in aerosols.

The survival of Chlamydia pneumoniae in aerosols was investigated by using a chamber with a capacity of 114.5 liters. We injected 5 x 10(7) inclusion-forming units (IFU) of C. pneumoniae in aerosols with a droplet size of 3 to 5 microns. Samples were taken after 30 s and every 1 min thereafter. The survival of C. pneumoniae was measured at four temperatures (8.5, 15, 25, and 35 degrees C) and at three different relative humidities (RH) of 5, 50, and 95% for each temperature. The survival rates of Streptococcus pneumoniae, Streptococcus faecalis, Klebsiella pneumoniae, Chlamydia trachomatis LGV2, and cytomegalovirus were also determined at 25 degrees C and 95% RH and compared with that of C. pneumoniae. At the mentioned temperatures and RH, a rapid decrease of C. pneumoniae IFU was observed in the first 30 s. After this the decrease in the number of IFU was more gradual. The survival of C. pneumoniae in aerosols were optimal at 15 to 25 degrees C and 95% RH; it was good compared with those of other microorganisms. A lower death rate was observed only in S. faecalis. In C. trachomatis, the death rate during the first 30 s was higher than that in C. pneumoniae (85 and 53.3%, respectively). After the first 30 s, the death rates in the two organisms were identical. It was concluded that transmission of C. pneumoniae via aerosols was possible. There is probably a direct transmission from person to person, taking into account the relatively short survival period of C. pneumoniae in aerosols.     

Field and in vitro assay of three methods for freezing ram semen

Glycerol has been the most widely used cryopreservation agent for spermatozoa and a wide range of factors affect its action on sperm viability and fertilizing capacity. We tested three methods for freezing ram semen packed in 0.25 ml straws (final cellular concentration: 100 x 10(6) spz/ml). Method M1: Two-thirds of the final volume of diluent was added as solution A (without glycerol) to the pure semen at 35 degrees C. The sample was cooled to 5 degrees C (-0.30 degrees C/min), one-third of final diluent volume was added as solution B (final concentration of glycerol 4%) and the sample was maintained at 5 degrees C for 2h. It was then frozen in a programmable biofreezer (-20 degrees C/min down to -100 degrees C). Method M2: The sample was diluted with a specific solution at 35 degrees C (final concentration of glycerol 3%), cooled to 5 degrees C (-0.20 degrees C/min) and left for 2h. After that, it was frozen in nitrogen vapours. Method M3: Semen was diluted 1:1 in a specific solution (concentration of glycerol 2%) and cooled to 5 degrees C (-0.25 degrees C/min). The sample was then diluted again in the same solution to the final cellular concentration (final concentration of glycerol 4%). It was left for 1h at 5 degrees C and then frozen in a programmable biofreezer (-20 degrees C/min down to -100 degrees C). Best total motility (TM) and progressive motility (PM) (75.8 and 55.18%) were obtained using Method M3. Methods M1 and M3 gave significantly higher values (P<0.05) for kinetic parameters: average path velocity (VAP) (81.3 and 85.2 microm/s), straight-line velocity (VSL) (72.8 and 77.3 microm/s) and linearity (LIN) (66.6 and 68.8%). Method M2 showed the lowest kinetic parameters of motility (VAP 74.4, VSL 67.3 and LIN 62.5) and the highest percentage of cells with damaged plasma membrane (53.8%). Method M1 gave the worst results in viability and acrosome status assessed using fluorescence probes (31.3%-dead cells with damaged acrosomes-versus 25.4% in M2 and 23.3% in M3). A field trial carried out on fertility showed a significantly higher percentage of pregnant or lambing ewes (P<0.05) with Method M3 (67.3% versus 51.1% for M1 and 58.8% for M2). We concluded that the use of a simple dilution medium (test-fructose-glycerol-egg yolk) with the addition of glycerol (to 2% at 35 degrees C and to 4% at 5 degrees C) in two steps together with a programmable biofreezer was a productive method for freezing ram semen.     

Effect of seminal plasma on the cryopreservation of equine spermatozoa

Seminal plasma is generally removed from equine spermatozoa prior to cryopreservation. Two experiments were designed to determine if adding seminal plasma back to spermatozoa, prior to cryopreservation, would benefit the spermatozoa. Experiment 1 determined if different concentrations of seminal plasma affected post-thaw sperm motility, viability and acrosomal integrity of frozen/thawed stallion spermatozoa. Semen was washed through 15% Percoll to remove seminal plasma and spermatozoa resuspended to 350 x 10(6)sperm/mL in a clear Hepes buffered diluent containing either 0, 5, 10, 20, 40 or 80% seminal plasma for 15 min, prior to being diluted to a final concentration of 50 x 10(6)sperm/mL in a Lactose-EDTA freezing diluent and cryopreserved. Sperm motility was analyzed at 10 and 90 min after thawing, while sperm viability and acrosomal integrity were analyzed 20 min after thawing. Seminal plasma did not affect sperm motility, viability or acrosomal integrity (P>0.05). Experiment 2 tested the main affects of seminal plasma level (5 or 20%), incubation temperature (5 or 20 degrees C) and incubation time (2, 4 or 6 h) prior to cryopreservation. In this experiment, spermatozoa were incubated with 5 or 20% seminal plasma for up to 6h at either 5 or 20 degrees C prior to cryopreservation in a skim milk, egg yolk freezing extender. Samples cooled immediately to 5 degrees C, prior to freezing had higher percentages of progressively motile spermatozoa than treatments incubated at 20 degrees C (31 versus 25%, respectively; P<0.05), when analyzed 10 min after thawing. At 90 min post-thaw, total motility was higher for samples incubated at 5 degrees C (42%) compared to 20 degrees C (35%; P<0.05). In addition, samples containing 5% seminal plasma had higher percentages of total and progressively motile spermatozoa (45 and 15%) than samples exposed to 20% seminal plasma (33 and 9%; P<0.05). In conclusion, although the short-term exposure of sperm to seminal plasma had no significant effect on the motility of cryopreserved equine spermatozoa, prolonged exposure to seminal plasma, prior to cryopreservation, was deleterious.     

Optimum Skin Blending Method for Quantifying Poultry Carcass Bacteria

Optimum blending fluids and blending times for use in quantifying bacteria on poultry carcass skin by the skin "blending" method were determined. Butterfield's buffered-phosphate diluent, physiological saline solution (0.85% NaCl), peptone water (0.1% peptone), and deionized water, each at four different skin blending times of 1, 2, 3, and 4 min, were compared. The comparison was based on relative numbers of bacteria per cm(2) of skin, enumerated by each combination on turkey carcasses. Peptone water and physiological saline solution each yielded significantly (P < 0.01) higher bacteria counts from turkey carcass skin samples than did Butterfield's buffered-phosphate diluent or deionized water. There were no significant differences among the four skin blending times and no significant interaction effect between the two factors tested.     

Kinetic properties and storage stability of catalase immobilized on to florisil

The covalent immobilization of bovine liver catalase (CAT) on to florisil via glutaraldehyde was investigated. Optimum immobilization pH and temperature were determined as pH 6.0, 10 degrees C respectively, while the amount of initial CAT per g of carrier and immobilization time was determined as 5 mg g(-1) and 120 min, respectively. The Vmax values for free and immobilized CAT were found to be 1.7 x 10(5) and 2.0 x 10(4) micromol H2O2 min(-1) mg protein(-1), respectively, whereas KM values were 33.3 mM and 1722.0 mM respectively. Operational stability was determined by using a stirred batch-type column reactor. Immobilized CAT retained about 40% of its initial activity after 50 uses. It showed higher storage stability than free CAT at 4 degrees C and 25 degrees C. Its storage stability increased with increasing relative humidity (RH) from 0 to 20% of the medium. The highest storage stability was obtained in 20% RH, however, further increase in RH from 40 to 100% significantly decreased the storage stability.     

Sporicidal Effect of Peracetic Acid Vapor

The sporicidal activity of peracetic acid (PAA) vapor at 20, 40, 60, and 80% relative humidity (RH) and 25 C was determined on Bacillus subtilis var. niger spores on paper and glass surfaces. Appreciable activity occurred within 10 min of exposure to 1 mg of PAA per liter and 40% or higher RH. The sporicidal rate decreased from the optimum at 80% RH to a slight effect at 20% RH. Spores on an impermeable surface were more difficult to kill than those on a porous one, probably because the cells tend to pile up on an impermeable surface and the vapor penetrates poorly through the layer of covering cells.