Research note: evaluation of direct plating for detecting Salmonella enteritidis in pools of egg contents

The effectiveness of direct plating of incubated egg contents pools onto selective agar media for detecting contamination by Salmonella enteritidis (SE) was evaluated in comparison to several broth enrichment strategies. Pools of mixed liquid whole egg were inoculated with very small number of SE cells, incubated for 4 days at 25 C, and sampled by direct plating or both enrichment culture. Methods involving broth nonselective (pre-enrichment) and selective broth culture steps detected a significantly higher percentage of contaminated egg pools than did direct plating, but required 48 h longer to provide results. Methods involving direct selective broth enrichment, without prior pre-enrichment, did not perform significantly better than direct plating. Direct plating appears to provide a relatively rapid and inexpensive method for detecting SE in egg pools, although greater sensitivity is attainable with more intensive methods.