Evaluation of coagglutination test for serotyping of enteropathogenic bacteria

Results of conventional agglutination and coagglutination (COA) tests for serotyping of enteropathogenic Escherichia coli (EPEC), Shigella, Salmonella and Vibrio cholerae were compared. Eighty isolates of different serotypes of EPEC falling in the Wellcome polyvalent (OK) 2, 3 and 4 antisera, showed good (4+) agglutination with COA reagent up to 1:960 dilution. Out of 50 strains of Shigella species tested, 25 of Sh. dysenteriae and 5 of Sh. sonnei gave good reaction up to 1:1920 dilution and 15 of Sh. flexneri up to 1:960 dilution in COA test. Similar reaction (4+) by 5 strains of Sh. boydii was seen up to 1:480 dilution only. All 100 isolates of different Salmonella species viz., S. paratyphi A (5), S. typhimurium (50), S. typhi (15), S. weltevreden (5) and S. senftenberg (25), when serotyped by COA, gave good reaction in 1:480 dilution except S. typhi factor 9 and dH antisera, which gave very weak reaction at 1:480 dilution and good reaction at 1:280 dilution. All seven isolates of V. cholerae gave good reaction in COA test even up to 1:1920 dilution. No cross reaction with any COA reagent was obtained in the 1206 heterologus isolates tested. Thus due to its higher efficiency, lower cost and good specificity, COA may prove to be a better method for serotyping of enteropathogens.