Effect of Relative Humidity on the Penetrability and Sporicidal Activity of Formaldehyde

The effect of relative humidity (RH) on formaldehyde penetration of paper, glassine, and cotton was determined by the death rate of bacterial spores in glass tubes covered with these materials. The data show that paper is readily penetrated regardless of RH, but the RH greatly affects the penetration rate of glassine and cotton. A comparison was also made of the effect of RH on the penetrability of formaldehyde generated from Formalin and paraformaldehyde. At low RH, all three closures were penetrated more readily by formaldehyde from paraformaldehyde than from Formalin, but no difference in the two was observed at high RH. It is felt that the difference at low RH is primarily due to the condensation of the vaporized Formalin.     

Microbiological Aspects of Ethylene Oxide Sterilization: III. Effects of Humidity and Water Activity on the Sporicidal Activity of Ethylene Oxide

An investigation determined the effects of environmental moisture content or water activity (Aw), exposure humidity, and sterilant concentration on the resistance of microbial spores. Decimal reduction values [expressed as D values at 54.4 C-specified concentration (milligrams per liter) of ethylene oxide] were determined from spore destruction curves of Bacillus subtilis var. niger dried on hygroscopic and nonhygroscopic surfaces. Four groups of spore preparations were preconditioned in one of four Aw environments (<0.1, 0.1, 0.5, 0.95) for 2 weeks or longer and were exposed to 500 mg of ethylene oxide per liter at 54.4 +/- 3 C and 10, 50, and 95% relative humidity in a specially designed thermochemical death rate apparatus. A fifth group did not receive any preconditioning treatment and was exposed immediately after preparation, in the same apparatus at the same temperature, to ethylene oxide concentrations of 200, 400, 600, 800, and 1,200 mg/liter and relative humidities of 15, 30, 50, 60, and 90%. The resistance of the spores on both types of surfaces to ethylene oxide increased proportionately with the Aw of the conditioning environment. The study also showed that moisture in the exposure system was not as critical a variable as the ethylene oxide concentration. The spore destruction rates, irrespective of the carrier types at all concentrations and at different humidities, varied little from one another. The decimal reduction values were reduced as the ethylene oxide concentration increased, and no optimal exposure humidity concentration was observed.     

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.     

Effect of Propylene Oxide Treatment on the Microflora of Pecans

Studies were conducted to determine the effectiveness of propylene oxide (PO) treatment in controlling the microflora of pecans. As used commercially, PO has little effect on internal bacteria and fungi in pecan halves. Tests of surface washings of commercially treated pecans showed a reduction of 96% in coliform bacteria following PO treatment. Under controlled laboratory conditions, PO gave 80 to 92% reduction of surface microflora and at least 64% reduction of internal flora, but neither bacteria nor fungi could be eliminated completely, even with high dosages. Current assay methods for determining bacterial content of nutmeats were shown to be inadequate because they utilize only surface washings and thus do not give an accurate picture of the total bacterial population of the nutmeat. Consequently, such assays do not permit an accurate assessment of any potential health hazard related to these organisms.     

Bactericidal Activity of Catecholamine Copper Complexes

Washed or growing E. coli cells are killed by epinephrine, norepinephrine or dopamine in the presence of non lethal concentrations of Cu(II). Killing is enhanced by anoxia and by sublethal Concentrations of H₂O₁. The rate of killing is proportional to the rate of catecholamine oxidation. The copper epinephrine complex binds to E. coli cells, induces membrane damage and depletion of the cellular ATP pool. The cells may be partially protected by SOD or catalase but not by OH radical scavengers. Addition of H²O₂ to cells which were sensitized by preincubation with the epinephrine-copper complex, causes rapid killing and DNA degradation. Sensitized cells are not protected by BSA.     

Bactericidal Activity of Catecholamine Copper Complexes

Washed or growing E. coli cells are killed by epinephrine, norepinephrine or dopamine in the presence of non lethal concentrations of Cu(II). Killing is enhanced by anoxia and by sublethal Concentrations of H₂O₁. The rate of killing is proportional to the rate of catecholamine oxidation. The copper epinephrine complex binds to E. coli cells, induces membrane damage and depletion of the cellular ATP pool. The cells may be partially protected by SOD or catalase but not by OH radical scavengers. Addition of H²O₂ to cells which were sensitized by preincubation with the epinephrine-copper complex, causes rapid killing and DNA degradation. Sensitized cells are not protected by BSA.     

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 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.     

Effect of Temperature on the Sterilization of Isopropyl Alcohol by Liquid Propylene Oxide

Liquid propylene oxide added to a solution of isopropyl alcohol and incubated at different temperatures markedly reduced the time required to sterilize the alcohol solution.     

Effect of Relative Humidity on Dynamic Aerosols of Adenovirus 12

Dynamic aerosols of adenovirus 12 were generated in the same Henderson apparatus under conditions of high, medium, and low relative humidity. High relative humidities resulted in more recovery of adenovirus 12 from aerosols and lungs of newborn Syrian hamsters. At 89, 51, and 32% relative humidity, the total infectious virus recovered from a 20-min aerosol was 10(6.7), 10(6.0), and 10(4.3) TCD(50), respectively. Hamsters exposed to these 20-min aerosols retained measured lung doses of 10(3.0), 10(2.4), and 10(1.0) TCD(50), respectively. The measured retained lung doses were compared to calculated inhaled lung doses based on both total virus aerosolized and total virus recovery from the aerosols.     

Bactericidal Activity of a Broad-Spectrum Illumination Source

Several hours of exposure to Vita-Lite lamps, which have a unique spectral distribution, give significant killing of cells of Staphylococcus aureus.     

Effects of Relative Humidity on Carbon Isotope Fractionation in Plants

Four C₃ plants and a C₄ plant were grown from seeds at four levels (30, 45, 60, and 75 %) of relative humidity. All plants were subjected to a 16 h day, at 500 μE/m².s^?1 photon flux density. Mature leaves were analyzed for their carbon isotopic composition. Isotope fractionation decreased by up to 3 ‰ with decreasing relative humidity in all C₃ plants, while the opposite trend was observed in the C₄ plant. The observed shifts in both C₃ and C₄ plants are attributed to decreased stomatal conductance at low relative humidity, resulting in a smaller P_i.     

The Effect of Relative Humidity and Light on Air-Dried Organisms

S ummary : The effect of relative humidity (RH) and inositol on the lethal action of artificial sunlight has been studied. The lethality of these radiations is shown to be strongly dependent on RH provided the intensity of the light is not too great. A critical region between 55 and 65% RH exists in which there is an abrupt change in the sensitivity of airborne cells to all wavelengths tested. Not only does the death rate change suddenly in this RH region but so also does the rate of mutant production. This critical RH region corresponds to the RH level at which bound water is removed from the nucleic acid bases and it is suggested that these water molecules are able to prevent lethal excitations or migration of excitation energy. Inositol is shown to prevent radiation damage and, because of its structure, it is assumed to replace water in the dried cells. Some ramifications of these findings with respect to the maintenance of cell integrity are discussed.     

Regulation of Stomatal Defense by Air Relative Humidity

It has long been observed that environmental conditions play crucial roles in modulating immunity and disease in plants and animals. For instance, many bacterial plant disease outbreaks occur after periods of high humidity and rain. A critical step in bacterial infection is entry into the plant interior through wounds and natural openings, such as stomata, which are adjustable microscopic pores in the epidermal tissue. Several studies have shown that stomatal closure is an integral part of the plant immune response to reduce pathogen invasion. In this study, we found that high humidity can effectively compromise Pseudomonas syringae-triggered stomatal closure in both Phaseolus vulgaris and Arabidopsis (Arabidopsis thaliana), which is accompanied by early up-regulation of the jasmonic acid (JA) pathway and simultaneous down-regulation of salicylic acid (SA) pathway in guard cells. Furthermore, SA-dependent response, but not JA-dependent response, is faster in guard cells than in whole leaves, suggesting that the SA signaling in guard cells may be independent from other cell types. Thus, we conclude that high humidity, a well-known disease-promoting environmental condition, acts in part by suppressing stomatal defense and is linked to hormone signaling in guard cells.The phyllosphere is one of the most diverse niches for microbe inhabitation. Numerous bacteria can survive and proliferate on the surface of the plant without causing any harm (Lindow and Brandl, 2003). However, for a bacterial pathogen to cause disease, it must penetrate through the plant epidermis and be able to survive and proliferate inside the plant. The mode and mechanism of penetration into the plant tissue is a critical step for infection, especially for bacterial pathogens that rely on natural openings and accidental wounds on the plant surface to colonize internal tissues (Misas-Villamil et al., 2013). Stomata are an example of such openings, providing one of the main routes through which the foliar pathogen Pseudomonas syringae transitions from avirulent epiphytic to virulent endophytic lifestyles (Melotto et al., 2008). This abundant opening in the epidermal tissue is not a passive port that allows unrestricted entry of microbes. It has been shown that plants are able to respond to human and plant bacterial pathogens by actively closing the stomatal pore (McDonald and Cahill, 1999; Melotto et al., 2006; Gudesblat et al., 2009; Zhang et al., 2010; Roy et al., 2013; Arnaud and Hwang, 2015), a phenomenon described as stomatal immunity (Sawinski et al., 2013). Several lines of evidence point to the complexity of this response and show that stomatal closure is an integral basal plant defense mechanism to restrict the invasion of pathogenic bacteria into plant tissues (Ali et al., 2007; Melotto et al., 2008; Zhang et al., 2008; Gudesblat et al., 2009). However, certain bacterial pathogens, such as Xanthomonas campestris pv campestris (Gudesblat et al., 2009), P. syringae pv syringae (Pss) B728a (Schellenberg et al., 2010), and P. syringae pvs tabaci, tomato, and maculicola (Melotto et al., 2006), can successfully cause disease by producing toxins that overcome stomatal immunity. Specifically, P. syringae pv tomato (Pst) DC3000 uses coronatine (COR) as such a toxin.In this study, we focused on elucidating environmental regulation of stomatal-based defense against bacterial invasion. Changes in environmental conditions, such as air relative humidity (RH), light, and carbon dioxide concentration regulate guard cell turgidity that consequently alters stomatal aperture size and the basic functions of stomata in plants, i.e. exchange of photosynthetic gases and regulation of water loss by transpiration (Zelitch, 1969; Schroeder et al., 2001; Fan et al., 2004). In natural conditions, plants are exposed to both biotic and abiotic stresses, and guard cells need to prioritize their response to the simultaneous occurrence of these stresses. For instance, it is a common observation that severe outbreaks of bacterial disease in the field are often associated with periods of heavy rain or high air humidity (Goode and Sasser, 1980). Mechanical wounding of plant tissues by rain might be one way that allows pathogens to bypass the stomatal route and gain unprecedented access to the plant interior. Additionally, the formation of large bacterial aggregates under high humidity on the leaf surface (Monier and Lindow, 2004) and splashing of bacteria during rain may also contribute to the spreading of disease at a higher rate. Interestingly, to ensure infection in the laboratory, researchers commonly expose plants to very high humidity for an extended period after surface inoculation. Here, we demonstrate that high RH compromises stomatal defense in Arabidopsis (Arabidopsis thaliana) and common bean (Phaseolus vulgaris) against P. syringae, allowing more bacteria to enter the leaf tissue and contributing to severe infections. Compromised bacterial-triggered stomatal closure due to high RH is accompanied by changes in plant hormone signaling in Arabidopsis. Specifically, high RH leads to activation of the jasmonic acid (JA) signaling pathway and down-regulation of the salicylic acid (SA) signaling in guard cells. These results connect plant physiology with epidemiology and advance the current understanding of foliar bacterial infection in plants.     

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.     

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.     

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.     

The Bactericidal Activity of Lectins from Nitrogen-Fixing Bacilli

Lectins I and II isolated from the nitrogen-fixing soil bacterium Paenibacillus polymyxa 1460 were found to be able to suppress the growth of Rhizobium leguminosarum 252 and Bacillus subtilis 36 at nearly all the concentrations tested (from 1 to 10 g/ml). Lectin I was also inhibitory to Azospirillum brasilense 245 and Erwinia carotovora subsp. citrulis 603, while lectin II exerted bactericidal activity against Xanthomonas campestris B-610 and B-611 and A. brasilense 245. The bacillar lectins incubated with Rhizobiumand Azospirillum cells caused leakage of low-molecular-weight substances from the cells, presumably resulting from impairment of the membrane barrier function. We believe that one of the possible mechanisms of the bacterial growth inhibition by lectins is mediated by the lectin-specific receptors occurring on the bacterial membrane, whose interaction with the lectin molecules induces conformational alterations in the membrane and concurrent malfunction of the metabolism of bacterial cells.     

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.     

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.