S. sonnei fase antisera



S. sonnei consists of two phases. The two phases can be differentiated morphologically, as phase I occurs in the form of smooth colonies, whilst phase II occurs in the form of rough colonies. It is therefore crucial that a suitable culturing medium is chosen, as the transformation between the two phases is dependent on, among other factors, the concentration of divalent cations. The higher the concentration of divalent cations, the more rough colonies there are (phase II). A patient sample will usually contain both types of colony.
The antigen that identifies a phase II colony is a subset of the antigen that identifies the phase I colonies. Phase I colonies will therefore agglutinate in phase I sera, but some phase I strains will also agglutinate in phase II sera. Phase II colonies will agglutinate only in phase II sera.

Product description

S. sonnei antiserum is produced by immunising rabbits with killed whole cells from phase 1 or phase 2 bacteria (as above - monoclonal product). The product is supplied in a vial with 3 mL ready-to-use antiserum, sufficient for at least 150 tests.


The Shigella strain is cultured overnight on a selective or a non-selective agar plate. A small colony is transferred to a slide and mixed with a drop of antiserum, and the slide is tilted slowly back and forth. If the bacterial colony has antigens that are homologous with the antiserum used, the cells will form antigen-antibody bonds, and clear aggregates will appear (agglutination). The result is read within 5-10 seconds of mixing. The reading is easiest to perform and clearest if the slide is held up in front of a light source against a black background.

Product range 


Product Number
of tests 
66446  S. sonnei phase I 
150  3 mL vial
66447  S. sonnei phase II antiserum  150  3 mL vial



SSI Diagnostica A/S
Herredsvejen 2
3400 Hillerød

Tel.: +45 4829 9100 (switchboard)

Tel.: +45 4829 9178


Frequently asked questions about S. sonnei fase antisera.


Packaging inserts