Rapid Identification of Cl. welchii by the Nagler Reaction

Abstract

The usual criterion, apart from morphology and colony form, is a "stormy" clot in litmus milk. This test is unreliable because some Clostridium welchii are non-clotters and it may be negative if the inoculum is too small. It failed in 32 of 58 strains tested. The clot may also occur without C. welchii, especially with a mixture of aerobes and anaerobes. Nagler''s (1939) reaction[long dash]"the production by welchii toxin of turbidity and sometimes a fine curdiness in human serum"[long dash]is a reliable diagnostic test and has the advantage of being serologically specific. The technic of Nagler''s reaction is fully descr. Nagler recommends in-activation of the serum; Hayward finds this unnecessary and undesirable. A mixture of equal parts of Fildes broth and human serum is preferred for the test. Egg-yolk saline (Macfarlane, et al. 1941 and Nagler, 1941) is a possible substitute for serum; it is more sensitive to welchii toxin but is a poorer supporter of growth. A single colony inoculum is sufficient for the Nagler test. For routine rapid identification the test should be applied to every suspected colony. The broth-serum culture should be incubated anaerobically. Identification is usually possible within 24 hrs.