Figure 1.

Different temperatures affect mucoviscosity and overall virulence of the convergent K pneumoniae ST307 strain PBIO1953. (A) Staining of capsular polysaccharides revealed a temperature-dependent change from a “normal” mucoid phenotype (yellow-beige colonies) to a hypermucoid phenotype (black colonies) at 40°C and 42°C. (B) The hypermucoviscosity was associated with a decrease in sedimentation upon centrifugation at 1,000 x g for 5 min. Results are shown as mean and standard error of percentage OD₆₀₀ remaining in the supernatant after centrifugation (n = 3). (C) Temperatures above 37°C resulted in increased adhesion to plastic surfaces. Results are expressed as growth-adjusted specific biofilm formation. The line in the box indicates the median value (n = 3). (D) The in vivo infection model showed a temperature-dependent increase in mortality rates. Kaplan-Meier plot of survivability rates of the G. mellonella larvae (n = 30). Results are expressed as mean percent of survivability after injection of 10⁵ CFU/larvae. For all results, mucoviscosity-associated characteristics at the different temperatures were compared to 37°C using analysis of variance (one-way ANOVA with Dunnett’s multiple comparison post hoc test); ns, not significant; P* <0.05; **P <0.01. RT, room temperature. (E) Scanning electron micrographs of PBIO1953 at 28°C, 37°C, 40°C, and 42°C at 20,000x magnification, scale bar = 200 nm (inserts: 10,000x magnification, scale bar = 1 µm), arrowheads show fimbriae-like structures.