Figure 2. Effect of changes in histidine content on enamel birefringence. (A-D) Images of ground sections under a polarizing microscope, demonstrating enamel birefringence. The WT enamel displayed birefringence, separating it from the adjacent dentin. In contrast, this birefringence was lost in KO, His+ and His- mice. (E-H) Images of molars embedded in resin. Compare the WT enamel occlusal surface characterized by cusps, grooves, and ridges, while the molars from Amel null and histidine mutant mice displayed a rough tooth surface and a worn-down occlusal surface.
Figure 3. Reduced enamel thickness and matrix configuration in Histidine mutant mice as revealed by microCT analysis (C,D versus A) and by semithin sections (F-I). Wild-type (A) and amelogenin null enamel preparations (B) are displayed for comparison. Note the reduced thickness of the enamel layer in Histidine plus (C) and Histidine minus mice (D). Quantitative comparison (E). Wild-type semithin sections of three days postnatal first mandibular mouse molars (F) display adjacent enamel (en, blue) and dentin (de, purple) mineralized tissues, revealing the representative enamel prism fishbone pattern. There were substantial differences between ameloblast (am) and enamel matrix (mx, arrow) shape and structure between all four groups. In comparison to wild-type controls (WT), His plus ameloblasts (G) contained ampulla-shaped vacuoles while there were distinct translucent vesicles in histidine-minus ameloblasts (H). The ameloblasts of amelogenin null mice were interrupted by metachromatic, spindle-shaped matrix deposits. The area of the developing enamel layer of wild-type mice (F) featured a thin layer of globular matrix deposits (mx, arrow) in His plus mice, while His minus mice were characterized by a thin, irregular shaped enamel matrix layer (mx, arrow). Amelogenin null mice highlighted minute matrix deposits only at the secretory tip of ameloblast Tomes processes (mx, arrow). The odontoblast (od) and the predentin layer (pd) were labeled for orientation.
Figure 4. Representative SEM and TEM micrographs illustrating the changes in histidine content on enamel matrix configuration, prism and crystal structure as revealed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). (A-D) SEM analysis of the shape and organization of enamel prisms. The WT enamel prisms displayed the typical herringbone decussation pattern, with individual crystals bundled into sheaths and prisms. In contrast, the apatite mineral crystals in the enamel region of KO mice were fused into short and densely organized, flower-shaped subunits. The enamel of His+ and His- mice was densely packed into trapezoid bundles (His+, C) or wrought into parallel arrangements (His-, D), abolishing the decussating pattern of their wild-type counterparts. (E-H) Transmission electron microscopy of wild-type mice revealed regular assemblies of nanosphere patterned proteins and initial protein-coated enamel crystals (E). Amelogenin null samples lacked the dense protein coat surrounding elongating crystals (F). Half of the apatite crystals (en) in amelogenin His+ samples were oriented perpendicular to the principal orientation of the crystals from the ameloblast to the dentin surface (en), while matrix subunits (mx) measured 2nm instead of 20nm in diameter (G). Crystal shapes in the His- samples featured uncoated enamel ribbons (rib) instead of crystals, while the matrix (mx) was dissociated from crystal surfaces and lacked the regular matrix pattern observed in the wildtype control (H).
]]>Listeria monocytogenes, Pseudomonas fluorescens, Escherichia coli, and Salmonella typhimurium, reference strains alone and in combination, were selected for their relevance to food safety and spoilage. Biofilm formation was assessed using microtiter plate assays. Temperature-dependent biofilm formation was evaluated at 25°C and 30°C, and incubated for 72 hours to reflect temperatures relevant to food processing, storage and optimal bacterial growth. Biofilm biomass was quantified using the crystal violet staining technique.