Journal of Immunological Methods, 137 (1991) 1-8 © 1991 Elsevier Science Publishers B.V. 0022-1759/91/$03.50 ADONIS 0022175991000871 JIM 05830 Rapid and sensitive detection of Salmonella (0 : 6,7) by immunomagnetic monoclonal antibody-based assays John M.e. Luk and AU A. Lindberg Karolinska Institute, Department of Clinical Bacteriology, Huddinge Hospital, Stockholm, Sweden (Received 27 July 1990, revised received 8 October 1990, accepted 22 October 1990) 1 An irnmunomagnetic technique to detect and identify Salmonella serogroup C] has been developed. Monoclonal antibodies (MAbs) specific for the 0 antigen 6,7 of Salmonella lipopolysaccharide (LPS) coupled to magnetic beads were used to isolate the salmonellae. Captured bacteria were easily identified by acridine orange staining and measured by enzyme immunoassays with a conjugate anti-LPS MAb as the detector probe. The whole detection process required 2-3 h and the sensitivity was 10 3_10 4 bacteriayrnl. The presence of blood (10%, v Iv) or stool (1%, wIv) components did not interfere with the im- munomagnetic assay performance. Key words: Monoclonal antibody; Magnetic bead; Salmonella 0: 6,7 lipopolysaccharide; Enzyme immunoassay Introduction Over the past decade the development of rapid and sensitive methods for detection of infectious microbial agents from clinical or food specimens has been of interest to many microbiologists and a range of techniques for the detection of the micro- bes or their antigens have emerged (Coonrod et al., 1983; Kohler, 1986). While ELISA and RIA systems performed either in microtiter plates, on nitrocellulose membranes, or in tubes are known to be highly sensitive, whereas counterimmuno- electrophoresis and latex agglutination or co-ag- glutination methods can provide more rapid re- Correspondence to: J.M.C. Luk, Department of Clinical Bacteriology, Karolinska Institute, Huddinge Hospital F82, S-141 86 Huddinge, Sweden (Tel.: (46) 8 -746 5186; Fax: (46) 8 - 779 4647). Abbreviations: BSA, bovine-serum albumin; CFU. colony- forming unit; ELISA, enzyme-linked immunosorbent assay; LPS, lipopolysaccharide; MAb, monoclonal antibody. sults (Fung and Tilton, 1985). More recently, a magnetic separation technique was introduced for tissue typing, cell sorting, subcellular organelle fractionation and DNA separation (Funderud et al., 1987; Lea et aI., 1988; Uhlen, 1989). This technique is considered to be of high efficiency and specificity, whilst remaining cheap and using simple equipment. Although the Salmonellae remain an important group of enteric bacterial pathogens causing gas- troenteritis ('food poisoning') and enteric fever in man (Cohen and Tauxe, 1986), the laboratory procedures for Salmonella identification by con- ventional culture methods are still laborious and time-consuming (normally taking at least 2-3 days to obtain a definitive result) (Edward and Ewing, 1972; Kelly et al., 1985). To facilitate the routine detection and identification of salmonellae, we have recently generated a panel of monoclonal antibodies (MAbs) specific for the a antigens of Salmonella serogroups A to E which account for > 95% of Salmonella infections in man today