Evaluation of a Centrifugation Method for the Detection of Salmonella enteritidis in Experimentally Contaminated...

Current recommendations for identification of Salmonella enteritidis ( SE ) contaminated eggs, as outlined by the USDA SE Task Force, require the combination of yolk and albumen from several eggs for room-temperature enrichment for 3 days prior to culture on solid medium. We describe the use of enzymatic digestion and chemical reduction to reduce viscosity and allow for concentration of Salmonella cells in egg albumen by centrifugation prior to enrichment and plating. In these studies, sanitized, intact, fresh shell eggs were inoculated with low numbers of viable SE . Albumen and yolk from six eggs in each group were separated; the albumen was pooled, treated with the proteolytic enzyme papain and the reducing agent N-acetyl-l-cysteine, and centrifuged, and the resulting pellet was incubated in tetrathionate broth (5 ml) at 37°C for 24 h prior to plating on brilliant green agar (BOA). For comparison, yolk and albumen from six eggs in each group were pooled, thoroughly mixed, and incubated at room temperature for 3 days prior to direct plating on BOA. Results from three trials indicated that the two culture techniques were equally sensitive for detection of Salmonella (range: 72 to 0.6 colony-forming units (CFU) of SE per pool). While as sensitive as the technique recommended by the SE Task Force, the centrifugation technique allowed more rapid (48 h) presumptive identification of Salmonella .