<prompt> Eleks gel precipitation test is used for detecting of toxins of which of the following organism?Corynebacterium diphtheriaeNeisseria meningitidisStreptococcus pneumoniaeAll the above  <response>: It is an in vitro test for diphtheria. A rectangular strip of filter paper impregnated with diphtheria antitoxin is placed on the surface of 20 normal horse serum agar in a petri dish while the medium is still fluid. If horse serum is not available, sheep rabbit serum may be used. When the agar has set, the surface is dried and narrow streaks of the strains are made at right angles to the filter paper strip. A positive and negative control should be set up. The plate is incubated at 37 degree for 24-48 hrs. Toxins produced by the bacterial growth will diffuse in agar and where it meets the antitoxin at optimum concentration will produce a line of precipitation. This precipitation lines indicate the strain is toxigenic. Ref: Ananthanarayanan panikers 8th ed Page 236. 