Journal de la technologie microbienne et biochimique

Abstrait

Morphological and Rheological Identification of Cocci Lactic Acid Bacteria

Elzeini HM, Ali AA, Nasr NF, Awad AA and Hassan AA

Lactic Acid Bacteria (LAB) widely distributed in nature and play an important role in many food fermentations. Bacterial cell morphology is useful and valuable parameters used in characterization of any organisms. Therefore, cell morphological shape and size of six strains of cocci LAB grown in two different media (M17 and RSM) were studied using scanning electron microscope (SEM) and image analysis technique. Topographical images reveal spherical or pseudo-spherical structures with height profiles and variation in size which occurred singly or in pairs, chains and tetrads. Cocci cells had a wide range of diameters (0.79-1.52 μm) with wide cells perimeters of 2.69 up to 5.54 μm. Cells growing in broth medium (M17) had higher surface areas and volumes being from 0.26 μm3 to 1.82 μm3. Some cocci cells were far away from being a perfect circle (0.639) while others had close to circle shapes. Cocci cells had a different orientation angles and surfaces seemed to have heights or extrudes with external boundary which were either a sharp outline or a rough surface. Cells hardness and wall thickness had an effect negatively or positively depending on the strain and growing medium. Rheological properties (viscosity, shear stress and torque) recorded different values. Shear stress followed the same trend as viscosity with maximum reached at different times (12 up to17 h). Clotting time was 11 up to17.7 h depending on the strain. According to acid production development, the fastest strain reached the iso-electric point (pH 4.6) was Str. thermophilus (12 h).