PMC:7723248 / 15073-23128 JSONTXT

{"target":"https://pubannotation.org/docs/sourcedb/PMC/sourceid/7723248","sourcedb":"PMC","sourceid":"7723248","source_url":"https://www.ncbi.nlm.nih.gov/pmc/7723248","text":"Results\n\nSalt\nThe viability of MS2, a non-enveloped virus, and Φ6, an enveloped virus, was examined in droplets of different compositions at RHs of 20%, 50%, and 80% by plaque assay. As shown in Fig 2A and 2C, the effect of sodium chloride on MS2 viability was RH-dependent. MS2 decayed more in 35 g/L NaCl droplets than in 0 and 1 g/L NaCl droplets at 20% RH, while the pattern was opposite at 80% RH. At 80% RH, the viability of MS2 was significantly higher in droplets containing NaCl than in those without it, suggesting that NaCl had a protective effect at this RH condition. At 50% RH, the relative viability of MS2 was lower than at the other RHs and was similar across all NaCl levels.\nFig 2 Concentration of bacteriophages (A) MS2 and (B) Φ6 in droplets with different initial sodium chloride concentration before (dark bars) and after (light bars) 1 h exposure to low, intermediate, and high RH (mean ± s.d. of triplicates). Relative viability of (C) MS2 and (D) Φ6 after 1 h exposure (lines shown the mean of triplicates). The number of virions in droplets at the start of the exposure experiments was 105−106 PFU. The enveloped virus, Φ6, was generally more susceptible than the non-enveloped one, MS2. Thus, the relative viability of Φ6 is shown on a log scale, whereas that of MS2 is shown on a linear scale. The relative viability of Φ6 was less than 10% in droplets containing NaCl at all RHs after 1 h (Fig 2B and 2D). At 20% RH, the relative viability was significantly lower in droplets containing NaCl, at concentrations of both 1 and 35 g/L compared to 0 g/L. At 50% RH, the relative viability was lowest in 1 g/L NaCl droplets, while it was significantly higher in droplets containing 0 and 35 g/L NaCl. At 80% RH, the relative viability was significantly higher in droplets containing 1 g/L NaCl compared to 35 g/L NaCl.\n\npH\nThe relative viability of MS2 in droplets at pH values of 4.0, 7.0, and 10.0 (i.e., acidic, pH-neutral, and basic) was generally similar at any one RH level (Fig 3A and 3C). At 20% RH, MS2 survived better, although not significantly, in pH-neutral droplets than in more acidic or more basic droplets. There were no significant differences in viability across pH at the other two RHs. Regardless of pH, viability was significantly lower at 50% RH compared to the other RHs.\nFig 3 Concentration of bacteriophages (A) MS2 and (B) Φ6 in droplets with different initial pH values before (dark bars) and after (light bars) 1 h exposure to low, intermediate, and high RH (mean ± s.d. of triplicates). Relative viability of (C) MS2 and (D) Φ6 after 1 h exposure (lines show the mean of triplicates). The number of virions in droplets at the start of the exposure experiments was 105−106 PFU. The dark gray dashed line indicates the detection limit (104 PFU/mL) of plaque assay. ND indicates no viable virus was detected. The relative viability of Φ6 differed significantly by pH, while the patterns in viability were similar across all three RHs (Fig 3B and 3D). At a pH of 4.0, no viable Φ6 was detected in either the control solution or the evaporating droplets after 1 h, suggesting a strong inactivation effect of acidic conditions on Φ6. At a pH of 10.0, the virus decayed by ~1–3 log10 units depending on RH, while the virus survived best in pH-neutral droplets (7.0), in which it decayed by ~1–2 log10 units depending on RH. At both these pHs, relative viability was greater at 20% RH compared to the two higher RHs.\n\nProtein\nSimilar to salt, the effect of protein on MS2 was also RH-dependent (Fig 4A and 4C). The relative viability of MS2 decreased as the concentration of BSA increased in droplets at 20% RH. However, at RHs of 50% and 80%, the relative viability was higher in the presence of BSA. At 50% RH, the viability of MS2 was reduced by only 7% in droplets containing 100 μg/mL BSA after 1 h, a significantly lower loss than the \u003e80% reduction in droplets that did not contain any BSA. At 80% RH, there was no decay in droplets containing BSA, regardless of its concentration, suggesting that BSA has a protective effect on the viability of MS2.\nFig 4 Concentration of bacteriophages (A) MS2 and (B) Φ6 in droplets with different initial protein concentration before (dark bars) and after (light bars) 1 h exposure to low, intermediate, and high RH (mean ± s.d. of triplicates). Relative viability of (C) MS2 and (D) Φ6 after 1 h exposure (lines show the mean of triplicates). The number of virions in droplets at the start of the exposure experiments was 105−106 PFU. Similar to its effect on MS2, BSA protected Φ6 from inactivation in droplets at intermediate and high RHs (Fig 4B and 4D). At 20% RH, the relative viability of Φ6 was similar in droplets with and without BSA. However, at 50% RH, the relative viability of Φ6 was significantly higher in droplets containing 1000 μg/mL BSA than in droplets with 0 or 100 μg/mL BSA. At 80% RH, the presence of BSA, regardless of its concentration, reduced the decay of Φ6 in droplets, suggesting its protective effect on viruses in droplets again.\n\nSurfactant\nThe relative viability of MS2 in droplets with different surfactant concentrations is shown in Fig 5A and 5C. MS2 generally survived better when SDS was present in droplets, and relative viability increased with SDS concentration at 20% and 80% RH. MS2 incurred no decay in droplets containing 10 μg/mL SDS, whereas it at least lost 25% viability in droplets containing no SDS. The relationship between viability and SDS concentration differed at 50% RH, at which MS2 survived best in droplets with 1 μg/mL SDS, but decayed most in droplets containing 10 μg/mL SDS. As shown in Fig 5B and 5D, SDS did not significantly affect the viability of Φ6 in droplets at RHs of 20%. However, 10 μg/mL SDS induced a significantly higher inactivation of Φ6 at RHs of 50% and 80%; no viable Φ6 was recovered from droplets containing 10 μg/mL SDS at high RH after 1 h.\nFig 5 Concentration of bacteriophages (A) MS2 and (B) Φ6 in droplets with different initial surfactant concentration before (dark bars) and after (light bars) 1 h exposure to low, intermediate, and high RH (mean ± s.d. of triplicates). Relative viability of (C) MS2 and (D) Φ6 after 1 h exposure (lines show the mean of triplicates). The number of virions in droplets at the start of the exposure experiments was 105−106 PFU. The dark gray dashed line indicates the detection limit (104 PFU/mL) of plaque assay. ND indicates no viable virus was detected.\n\nRelative humidity\nU-shaped patterns in the viability of MS2 against RH were observed in droplets composed of salt and surfactant, as well as in pH-adjusted droplets. Specifically, the relative viability of MS2 was lowest at 50% RH, while it was significantly higher at RHs of 20 and 80%. A different pattern was observed for the viability of MS2 in droplets containing protein, in which the relative viability of MS2 generally increased as RH increased. Two-way ANOVA indicated that there was a main effect of RH, but not salt or pH, on the viability of MS2 in droplets. In droplets composed of protein and surfactant, both RH and droplet composition (i.e., protein and surfactant) had a statistically significant effect on the relative viability of MS2. Meanwhile, there was an interaction effect between RH and droplet composition on the viability of MS2 in droplets containing salt, protein, and surfactant, but not between RH and the pH of droplet media.\nThe effect of RH on the viability of Φ6 was different from that on MS2. Instead of following a U-shaped pattern, the viability of Φ6 generally decreased as RH increased in droplets containing salt and surfactant, and in pH-adjusted droplets. The pattern was slightly different for droplets containing protein due to the protective effect from BSA, which made the trend more U-shaped. Statistical analysis suggests that there was a main effect of RH on the viability of Φ6 in droplets composed of surfactant. 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