Detection of Salmonella spp. by Conventional Bacteriology and by Quantitative Polymerase-Chain Reaction in Commercial Egg Structures

Abstract

Conventional bacteriology techniques and quantitative polymerase-chain reaction (qPCR) were applied to the eggshell, albumen, and yolk of washed and unwashed commercial white and brown eggs, to detect Salmonella spp. Pooled samples of eggshells, albumen, and yolk of white and brown eggs were collected at the poultry house and at the egg-storage room. Salmonella spp. was detected by conventional bacteriology in 5.4% (21/387) of analyzed samples and in 16% (68/387) by qPCR. In the 114 unwashed white eggs samples of eggshell, albumen and yolk, the bacterium was identified in 2.6% of the eggs (3/114) by conventional bacteriology and in 13.2% (15/114) by qPCR. In the 90 samples of washed eggs, 6.7% (6/90) were contaminated as detected by conventional bacteriology and 10.0% (9/90) by qPCR. In the 81 samples of unwashed brown eggs, Salmonella spp. was detected in 6.1% of the eggs (5/81) by conventional bacteriology and 27.2% (22/81) by qPCR. In the 102 samples of brown washed eggs, 6.9% (7/102) where positive by conventional bacteriology and 35.3% (16/102) by qPCR. All samples detected as positive by conventional bacteriology were also positive by qPCR. Salmonella Agona represented 18.2% (4/22) of identified serovars, Salmonella enterica subs. enterica O: 4.5 18.2% (4/22), Salmonella Schwarzengrund 18.2% (4/22), Salmonella Cerro 13.6% (3/22), Salmonella Anatum 13.6% (3/22), Salmonella Enteritidis 9.1% (2/22), Salmonella Johannesburg 4.5% (1/22), and Salmonella Corvallis 4.5% (1/22). The qPCR method provided better detection of Salmonella spp. in commercial eggs than conventional bacteriology. The conventional egg washing and disinfection procedures are not efficient to eliminate Salmonella.