Isolation of salmonellas by immunomagnetic separation

Magnetisable particles, coated with anti-salmonella serum, were used to isolate Salmonella livingstone from pure cultures, mixed cultures and food samples. Beads (10(7] were generally incubated with 10(4) Salm. livingstone cells/ml for 60 min at room temperature. The incubation and washing medium (0.01 mol/l phosphate-buffered saline; PBS) contained 0.1% bovine serum albumin (BSA) and 0.1% Tween 20, respectively. This method gave a recovery for Salm. livingstone of 51.0 +/- 7.8%. However, other micro-organisms such as Aeromonas hydrophila interfered with this test because of non-specific reactions (recovery 50.9 +/- 12.7%). These non-specific reactions could be decreased by using 4% skim milk instead of 0.1% BSA in the incubation medium. The ratio of the recovery of Salm. livingstone relative to the recovery of Aer. hydrophila changed from 0.9 when PBS with 0.1% BSA was used, to 13.4 when PBS with 4% skim milk was used. Immunomagnetic separation of Salmonella spp. from food samples offers good prospects for concentrating salmonella cells from heterogeneous bacterial suspensions, such as enrichment broths.