Mechanisms regulating the airborne survival of Klebsiella pneumoniae under different relative humidity and temperature levels.

In this study, Klebsiella pneumoniae was suspended in synthetic saliva in a nebulizer (N0 ) and nebulized for 5 min (N5 ) into an aerosol chamber and further prolonged in the aerosolization phase for 15 min (A15 ) under four different conditions: 20°C, 50% relative humidity (RH); 20°C, 80% RH; 30°C, 50% RH; and 30°C, 80% RH. Samples were collected at N0 , N5 , and A15 , then subjected to survival analysis and comparative transcriptomic analysis in order to help elucidate the underlying mechanisms of airborne survival. Survival analysis shows that a higher humidity and lower temperature were favorable for the airborne survival of K. pneumoniae, and the effect of RH was more remarkable at 20°C than that at 30°C. The RNA-seq results show that during the nebulization phase (N0 vs. N5 ), a total number of 201 differentially expressed genes (DEGs) were identified (103 downregulated and 98 upregulated). Comparison between nebulization and aerosolization phases (N5 vs. A15 ) indicates up to 132 DEGs, with 46 downregulated and 86 upregulated. The most notable groups of genes are those involved in cellular remodeling, metabolism and energy processes. Alarmingly, the mbl gene, which encodes antibiotic resistance in K. pneumoniae, was upregulated during the suspension phase under all the tested conditions. This study provides insights into the control of airborne transmitted diseases.