Influence of Relative Humidity on the Survival of Some Airborne Viruses

A system for studying the effects of relative humidity (RH) and temperature on biological aerosols, utilizing a modified toroid for a static aerosol chamber, is described. Studies were conducted at 23 C and at three RH levels (10, 35, and 90%) with four viruses (Newcastle disease virus, infectious bovine rhinotracheitis virus, vesicular stomatitis virus, and Escherichia coli B T3 bacteriophage). Virus loss on aerosol generation was consistently lower at 90% than at 10 or 35% RH. When stored at 23 C, Newcastle disease virus and vesicular stomatitis virus survived best at 10% RH. Infectious bovine rhinotracheitis virus and E. coli B T3 bacteriophage survived storage at 23 C best at 90% RH.     

Effect of Temperature and Relative Humidity on Survival of Airborne Columbia SK Group Viruses

Three strains of the Columbia SK (Col-SK) group of viruses [Mengo, Maus Elberfeld (ME), and Col-SK viruses] have been studied in the airborne state. All three strains were found to give identical aerosol decay patterns at 16 or 26 C, when held at the same relative humidity (RH). During the first 5 min of aerosol storage time at 16 C, virus inactivation was RH-dependent, with survival maximal at either high (greater than 80%) or low (less than 5%) RH. After 5 min at 16 C, further inactivation, regardless of RH, was insignificant. At 26 C, the effect on survival of RH between 40 and 60% was even more pronounced than at 16 C, and continued after 5 min through 6 hr. Results of this study indicated that the inactivation of airborne Col-SK group viruses was similar to that of other ribonucleic acid (RNA) viruses, particularly poliovirus. Since members of the Col-SK group are picornaviruses, they may well serve as an aerosol model representative of small, ether-resistant, single-stranded RNA viruses.     

Role of Relative Humidity in the Survival of Airborne Mycoplasma pneumoniae

Aerosols of Mycoplasma pneumoniae were studied at several relative humidities at a controlled temperature of 27 C. Production of an experimentally reproducible aerosol required preatomization of the organism in its suspending fluid and was dependent on the type of fluid used in atomization as well as on the procedures used to produce an aerosol. The airborne particles studied were within the range of epidemiological significance, with most being 2 mum or less in diameter. Survival of the airborne mycoplasma in these particles was found to be best at very low and at very high humidities. The most lethal relative humidity levels were at 60 and 80%, at which levels fewer than 1% of the organisms survived over a 4-hr observation period. However, survival of the organism at most relative humidity levels was such that long-term infectivity could be expected from aerosols of M. pneumoniae. Because of the extreme sensitivity of M. pneumoniae at critical humidity levels, control of the airborne transmission of these organisms may be possible in selected spaces.     

Effect of Relative Humidity and Temperature on Airborne Venezuelan Equine Encephalitis Virus

Inactivation of airborne Venezuelan equine encephalitis (VEE) virus disseminated from liquid suspensions or from lyophilized preparations as 1- to 5-mum particles was investigated under various conditions of relative humidity and temperature in a 2,500-liter static aerosol chamber. Relative humidity ranging from 18 to 90% at 24 C and temperature ranging from -40 to 24 C had no marked effect on the biological decay rate or the recovery of viable airborne VEE virus disseminated from liquid suspensions. However, at 49 C a significant increase in the biological decay rate and decrease in aerosol recovery of the VEE virus were observed. Airborne lyophilized VEE virus was significantly affected by relative humidity. An increase in relative humidity from 20 to 90% resulted in progressive decrease in aerosol recovery of viable VEE virus. A twofold reduction in aerosol recovery of the lyophilized virus was observed at and above 29 C as compared to the lower temperatures studied. However, the differences among biological decay rates of lycphilized VEE virus were not significant within temperature range of -40 to 38 C.     

Effect of Relative Humidity on the Inactivation of Airborne Serratia marcescens by Ultraviolet Radiation

Apparatus was designed and constructed in which a bacterial aerosol of known age, particle size, and relative humidity (RH) could be exposed to ultraviolet (UV) radiation of measured intensity for a given period of time and then be sampled quantitatively. Aerosols of Serratia marcescens were exposed to UV dosages between 96.0 and 0.75 (muw-sec)/cm(2) at humidities ranging from 25 to 90%. A sharp decline in the fraction of organisms killed was found at RH values above 60 to 70%. Above 80% RH, there was evidence for reactivation induced by UV. The plot of "log fraction organisms remaining" versus UV dose was curvilinear, suggesting noncompliance with the monomolecular law of reaction velocity, but the Bunsen-Roscoe law of reciprocity between time and intensity of UV exposure was demonstrated to hold. These results could be accounted for by postulating the presence in the aerosol of two populations of organisms with different sensitivities to UV, each individually obeying the monomolecular law of reaction velocity. The data amplify existing information on the relationship between UV disinfection of airborne organisms and RH. In the middle range of humidities, the sensitivity of the organisms to UV was greater than would be expected from published reports.     

The Effect of Relative Humidity on the Survival of Three Serotypes of Klebsiella

S ummary . Any factor which enhances the survival of human pathogens in the hospital environment can result in increased exposure of the patient to such pathogens and perhaps contribute to an increase in patient infections. Klebsiella serotypes 3, 9 and 69 were exposed on glass to relative humidities (R.H.) of 11, 33, 53 and 85%. Death rates for all serotypes, at a constant 25°, could be correlated with the amount of moisture in the air. Prolonged survival was demonstrated at 11 and 33% R.H. with an increased death rate at 53 and 85%. The implications of this phenomenon are discussed.     

Effect of Diluent and Relative Humidity on Apparent Viability of Airborne Pasteurella pestis

Airborne Pasteurella pestis (A-1122) at low humidities [20 to 50% relative humidity (RH)] exhibited exponential decay when either 1% peptone or Heart Infusion Broth (HIB) was used as the diluent in the viable assay system. At higher RH values (65 and 87%), however, the 1% peptone diluent adversely affected the viability assay. In contrast, HIB as diluent was remarkably effective in demonstrating a higher number of viable cells in aerosols held at high RH values. Similarly, with HIB as diluent, aerosols were shown to contain viable cells during 90 min of observation; with 1% peptone, viability was not detectable after 20 min in the airborne state.     

Effect of Relative Humidity on Survival of Candida albicans and Other Yeasts

Individual blastospores of Candida albicans were deposited on the surface of 50-mm membranes (Millipore Corp.) and placed within sealed glass chambers at various relative humidities (RH). After 48 hr, virtually all cells maintained at 100 and 10% RH had survived, but 84% of the cells maintained at 60% RH failed to develop into colonies when transferred to Sabouraud medium. No morphological abnormalities could be observed in cells surviving low RH values, but their initial rate of multiplication after transfer to Sabouraud medium was greatly reduced, compared to that demonstrated by cells maintained at 100% RH. At 60% RH, the exposure time required to kill 50% of the blastospores was 2 to 3.5 days. The inimical effect of 60% RH was confirmed in a total of 21 isolates of C. albicans. No deleterious effect was noted when 12 other species of yeasts were subjected to 10, 60, and 100% RH. The single isolate of Candida brumptii and 1 out of the 20 isolates of Cryptococcus neoformans tested also failed to grow after blastospores had been exposed to 60% RH for 4 days.     

Effects of Atmospheric Humidity and Temperature on the Survival of Airborne Flavobacterium

The survival of airborne Flavobacterium sp. in particle sizes ranging from 1 to 5 μm was significantly influenced by atmospheric temperature. A progressive increase in temperature from −18 to 49 C resulted in increases in death rates of the airborne organism. The lowest death rates were observed in the temperature range of −40 to −18 C, and the highest death rates were observed in the 29 to 49 C range. At 24 C, the survival of airborne Flavobacterium did not appear to be significantly affected by relative humidity ranging from 25 to 99%.     

Effect of Temperature and Relative Humidity on the Survival of Foodborne Viruses during Food Storage

Millions of people suffer from foodborne diseases throughout the world every year, and the importance of food safety has grown worldwide in recent years. The aim of this study was to investigate the survival of hepatitis A virus (HAV) and viral surrogates of human norovirus (HuNoV) (bacteriophage MS2 and murine norovirus [MNV]) in food over time. HAV, MNV, and MS2 were inoculated onto either the digestive gland of oysters or the surface of fresh peppers, and their survival on these food matrices was measured under various temperature (4°C, 15°C, 25°C, and 40°C) and relative humidity (RH) (50% and 70%) conditions. Inoculated viruses were recovered from food samples and quantified by a plaque assay at predetermined time points over 2 weeks (0, 1, 3, 7, 10, and 14 days). Virus survival was influenced primarily by temperature. On peppers at 40°C and at 50% RH, >4- and 6-log reductions of MNV and HAV, respectively, occurred within 1 day. All three viruses survived better on oysters. In addition, HAV survived better at 70% RH than at 50% RH. The survival data for HAV, MS2, and MNV were fit to three different mathematical models (linear, Weibull, and biphasic models). Among them, the biphasic model was optimum in terms of goodness of fit. The results of this study suggest that major foodborne viruses such as HAV and HuNoV can survive over prolonged periods of time with a limited reduction in numbers. Because a persistence of foodborne virus on contaminated foods was observed, precautionary preventive measures should be performed.     

Survival of Salmonella montevideo on Wheat Stored at Constant Relative Humidity

Eleven samples of Ottawa variety hard red winter wheat were inoculated with a standardized suspension of Salmonella montevideo. The contaminated wheat samples were placed in constant relative humidity (RH) chambers held at 25 C. Relative humidities were 7, 11, 22, 33, 43, 53, 62, 75, 84, 92, and 98%. Constant RH at 25 C was maintained with different saturated salt solutions in the sealed chambers. Periodic counts of viable S. montevideo cells per gram of wheat were made over a 28-week sampling period. Viable counts of S. montevideo on wheat held at 7, 11, and 22% RH decreased from an initial 10⁶ cells/g of wheat to a final count of 10⁴ cells/g in each sample. Samples stored at 33, 43, 53, and 62% RH decreased from 10⁶ viable cells/g to 3.6 × 10³, 10³, 10², and 20 viable cells/g, respectively. No viable S. montevideo cells were detected in the samples held at 75, 84, 92, and 98% RH after 22, 16, 26, and 16 weeks, respectively.     

Effect of Relative Humidity on Formaldehyde Decontamination

Death rate studies were conducted to determine the effect of varying the concentration, humidity, and type of surface on the sporicidal activity of formaldehyde gas. Washed and unwashed spores were similarly exposed to detect the influence of residual nutrient growth medium upon the rate of kill. The results indicated that the sporicidal activity of formaldehyde gas varies directly with its concentration. Relative humidities (RH) over 50% proved essential for sterility. Spores on a porous surface (cotton cloth) were more readily killed at lower RH than those on a nonporous surface (glass). The reverse occurred at very high RH. At 75% RH, the unwashed spores on glass were killed faster than the washed spores.     

Aerosol Survival of Pasteurella tularensis and the Influence of Relative Humidity

The aerosol survival in air was determined for Pasteurella tularensis live vaccine strain (LVS) as a function of relative humidity (RH). Three different preparations of bacteria were used: (i) liquid suspension of P. tularensis LVS in spent culture medium; (ii) powders of P. tularensis LVS freeze-dried in spent culture fluid; (iii) P. tularensis LVS freeze-dried in spent culture fluid and then reconstituted with distilled water and disseminated as a liquid suspension. Preparation (i) gave greatest survival at high RH and lowest survival at intermediate RH. Preparation (ii), in contrast, gave greatest survival at low RH and minimum survival at 81% RH. Preparation (iii) was the same as preparation (i), i.e., the process of freeze-drying and reconstituting with distilled water before aerosol formation had little or no effect upon aerosol survival as a function of RH. Hence, control of aerosol survival appears to be through the water content of P. tularensis LVS at the moment of aerosol generation rather than the water content of the bacteria in the aerosol phase.     

Response of Airborne Mycoplasma pneumoniae to Abrupt Changes in Relative Humidity

The effect of an abrupt change in the relative humidity on the viability of airborne Mycoplasma pneumoniae has been examined. When the microbial aerosols were permitted to equilibrate in air held at either low or high humidities and were then subjected to a sudden shift to a mid-range humidity, a significant loss (>90%) of the colony-forming units per liter of aerosol occurred within 8 min. In contrast, a change in the relative humidity of more than 18% in either direction from a lethal mid-range humidity noticeably decreased the rate of biological decay. Double humidity shifts (i.e., from dry to a mid-range level and then to a high humidity range) were very detrimental, with very few survivors after 8 min. These results indicate that the biological stability of airborne M. pneumoniae may be easily modified by a sudden change in the relative humidity, such as occurs in natural atmospheres. This increased sensitivity brought about by producing changes in relative humidity through the lethal humidity range may provide a method whereby the control of these organisms in naturally contaminated indoor air environments may be eventually achieved.     

Effect of Some Unicellular Algae on Escherichia coli Populations in Sea Water and Oysters

Acrylic acid was detected in sea water in which oysters had been maintained and was shown to be derived from unicellular algae containing dimethyl-β-propiothetin (DMPT). Anticoliform activity was noted in samples containing acrylic acid. Intensification of the effect was achieved in laboratory studies and Phaeodactylum tricornutum (DMPT present) caused a rapid decline of Escherichia coli populations in sea water and in oysters which had been fed this alga. Pavlova lutheri (DMPT absent) was ineffective against E. coli .     

Ribosome Specificity of Transfer Factors from Unicellular Algae

Abstract

Ribosome specificity of polymerizing enzymes prepared from Nostoc muscorum and from photosynthesizing and non-photosynthesizing strains of Euglena gracilis and Chlorella vulgaris was determined by assaying protein synthesis in vitro with Escherichia coli (70 S type) and Saccharomyces cerevisiae (80 S type) ribosomes. Polymerizing enzymes prepared from the prokaryote N. muscorum are active only on E. coli ribosomes, while the enzymes prepared from the photosynthesizing strains of E. gracilis and C. vulgaris are active on both 70 S and 80 S type ribosomes. Polymerizing enzymes from dark-grown cells of E. gracilis and of an achloric strain are active only on 80 S type ribosomes, and the activity on E. coli ribosomes may be restored by adding E. coli transfer factor T. In addition, activity on 70 S ribosomes becomes evident a few hours after exposure to light of dark-grown cells of E. gracilis. On the contrary, polymerizing enzymes prepared from a non-photosynthetic strain of C. vulgaris, and from the naturally occuring achloric alga Prototheca zopfii are active on both types of ribosomes. C. vulgaris and its achloric strain contain both 70 S and 80 S type ribosomes, while in P. zopfii only 80 S type ribosomes are evident.     

Fatty Acid Composition of Unicellular Strains of Blue-Green Algae

The fatty acids of 34 strains of unicellular blue-green algae provisionally assigned to the genera Synechococcus, Aphanocapsa, Gloeocapsa, Microcystis, and Chlorogloea by Stanier et al. have been chemically characterized. The strains analyzed can be divided into a series of compositional groups based upon the highest degree of unsaturation of the major cellular fatty acids. Twenty strains fall into the group characterized by one trienoic fatty acid isomer (alpha-linolenic acid), and seven strains fall into a group characterized by another trienoic acid isomer (gamma-linolenic acid). These groups in many cases correlate well with groupings based upon other phenotypic characters of the strains, e.g., deoxyribonucleic acid base composition. The assignment of a strain to a compositional group is not altered when the strain is grown under a variety of different culture conditions. All strains contain glycolipids with the properties of mono- and digalactosyldiglycerides.     

On the Properties of the Starch Granules from Unicellular Green Algae

Starch granules from Chlorella, Chlamydomonas and Scenedesmus, grown heterotro-phically in a medium containing organic carbon sources, were isolated by means of the toluol treatment of the sonicate of alga. The toluol treatment separated the starch granules in the water layer from the cells and cell debris coagulated in the upper toluol layer.

The starch granules of Chlorella vulgaris and Chlamydomonas sp. were composed of amylose (12 to 3%) and amylopectin. The amylose content of the starch granules of Scenedesmus basilensis was 22 %. All the X-ray diffraction patterns of algal starch obtained in this investigation were of the A-type, identical to that of corn starch.     

Effect of Temperature on Survival of Airborne Mycoplasma pneumoniae

Aerosols of Mycoplasma pneumoniae were prepared at each of eight relative humidities between 0 and 85% and at five separate temperatures between 10 and 43 C. Survival of these organisms was found to be a function of both relative humidity and temperature. However, the temperature response was mediated by humidity in that the effects of temperature could be observed only if some water vapor was present. At all temperatures, survival of M. pneumoniae in aerosols was found to be best at the extremes of relative humidity. The effects of temperature were such that irrespective of relative humidity an increase in temperature resulted in a decreased airborne survival time.