Why is semi solid media used to test for motility

Pancreatic digest of casein Save my name and email in this browser for the next time I comment. Objective To determine the motility of bacterium. To differentiate between motile and non motile bacteria. Principle Motility by bacterium is mostly demonstrated in a semi solid agar medium.

Be sure to keep the needle in the same line it entered as it is removed from the medium. Observe for a diffuse zone of growth flaring out from the line of inoculation.

Expected Results Positive: Diffuse, hazy growths that spread throughout the medium rendering it slightly opaque. Negative: Growth that is confined to the stab-line, with sharply defined margins and leaving the surrounding medium clearly transparent.

Uses It is used for the differentiation of microorganisms on the basis of motility in a laboratory setting. It is performed to assign taxonomic classification to organisms. Motility tests are important in characterization of pathogens. The tests are often employed in identification protocols in the family Enterobacteriaceae Motility test is also used for the species differentiation of gram positive cocci, Enterococci.

Enterococcus faecium and E. Limitations Some organisms will not display sufficient growth in this medium to make an accurate determination, and additional follow-up testing is required. It is recommended that biochemical, immunological, molecular, or mass spectrometry testing be performed on colonies from pure culture for complete identification. False-negative reactions may occur if bacterial flagella are damaged due to heating, shaking, or other trauma. Such environmental shock will render the organism non-motile.

Motility test helps us to differentiate between genera and species of bacteria. There are a variety of ways to determine the motility of a bacterium —biochemical tests as well as microscopic analysis.

For the wet preparation, a drop of the organism in broth is suspended on a clean glass slide, a coverslip is added, and the culture is observed microscopically for motility. Occasionally the organism is inoculated in a semisolid motility medium in a straight line down through the center of a tube and is incubated. Motile organisms will cause turbidity throughout the tube as they migrate out from the line of inoculation whereas nonmotile organisms will grow only along the line of inoculation.

Test each newly prepared or purchased motility test media for sterility and performance using standard bacterial isolates. In the laboratory, motility testing using a semi-solid medium is commonly used for the identification of gram-negative bacteria of Enterobacteriaceae family. Motility testing is done in conjunction with other biochemical testing using special biochemical media. Motility test is also used for the species differentiation of gram-positive cocci, enterococci.

Enterococcus faecium and E. Note: Incorporation of tetrazolium chloride at a final concentration of 0. The tetrazolium makes the motility agar much easier to read for motility. Tetrazolium is colorless in oxidized form, but the reduced salt is red occurring as a result of bacterial metabolism and indicates where bacterial growth has occurred. It is a simple and very useful test to differentiate Vibrio species gram-negative motile curved rod and Aeromonas species gram-negative motile rod.