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Detection of Salmonella in Foods by the Modified 1-2 Test
7.10 Selective Isolation
7.10.1 All 1-2 Tests with presumptively positive results (i.e. there is a distinct immunoband) must be confirmed by streaking onto selective agars. Any 1-2 Tests with obscure or irregular immunobands must be confirmed as positive or negative by streaking onto selective plates. When in doubt, streak from the side-arm onto the selective plates.
7.10.2 Streak the TBG from the side-arm (inoculation chamber) onto BIS and one other agar (BGS, EF-18, RAM, XLD, or HEK (8.7)). The agars are incubated at 35°C for 18-24 h, except for EF-18 agar, which is incubated at 42°C for 24 h. As needed, BIS and other agars are reincubated overnight.
7.10.3 From the selective agars, pick typical colonies and subculture on TSI and LIA slants. Incubate at 35°C for 18-24 h. Colonies may have to be purified on MacConkeys agar or RAM.
7.10.4 Proceed with biochemical and serological confirmation on the colonies subcultured to TSI and LIA slants (Table III) according to the procedures in MFHPB-20 (HPB, 1978; see Volume 2 of the Compendium of Analytical Methods).
7.10.5 Other confirmation tests can include the use of API-20E (API Laboratory Products Ltd., St-Laurent, Que.), Micro-ID (Organon Teknika Inc., Scarborough, Ont.), Enterotube (Roche Diagnostic Systems, Nutley, NJ), Vitek (bioMerieux USA, Hazelwood, MI), and an enzyme-linked antibody (ELA) method (8.1, 8.2).
8. REFERENCES
8.1 Todd, E.C.D., J.M. Mackenzie, L.J. Parrington, A.N. Sharpe, P.I. Peterkin, M. Diotte, M.A.J. Gidney, K. Nielsen, A. Fraser, K. Rahn, A.I. Tiffin, G. Paterson and W. Gehle. 1991. Evaluation of Salmonella antisera for an optimum enzyme-lined antibody detection of Salmonella using hydrophobic grid membrane filters. Food Microbiol. 8:311-324.
8.2 Todd, E.C.D., J.M. MacKenzie and P.I. Peterkin. 1993. Development of an enzyme-linked antibody hydrophobic grid membrane filter method for detection of Salmonella in foods. Food Microbiol. 10:87-99.
8.3 Nath, E.J., E. Neidert and C.J. Randall. 1989. Evaluation of enrichment protocols for the 1-2 Test for Salmonella detection in naturally contaminated foods and feeds. J. Food Prot. 52(7):498-499.
8.4 Oggel, J.J., D.C. Nundy and C.J. Randall. 1990. Modified 1-2 Test system as a rapid screening method for the detection of Salmonella in foods and feeds. J. Food Prot. 53(8):656-658.
8.5 Warburton, D.W., J. Oggel, B. Bowen, et al. 1993. A comparison study of the modified 1-2 Test and the standard HPB method in the isolation of Salmonella. Food Microbiol. 11:253-263.
8.6 Warburton, D.W., P.T. Feldsine and M.T. Falbo-Nelson. 1993. Modified immunodiffusion method to detect Salmonella in raw flesh and highly contaminated food types: collaborative study. J. Assoc. Off. Anal. Chem. submitted for publication.
8.7 Warburton, D.W., B. Bowen, A. Konkle, C. Crawford, et al. 1993. A comparison of six different plating media used in the isolation of Salmonella. Int. J. Food Microbiol. 22:277-289.
