Investigation of Salmonella contamination and disinfection in farm egg-packing plants

Aims: As part of a field-based study of the distribution and persistence of Salmonella infection on commercial egg-laying farms, sampling was carried out on one or more occasions in egg-packing areas of 12 farms infected with Salm. Enteritidis. Methods and Results: Salmonellas were isolated by cultural methods. Contamination was common, with Salmonella being found in 23.1% of floor swab samples, 30.8% of grading tables, 23.1% of conveyor belts or rollers and 23.8% of candlers. Four farms were sampled after cleaning and disinfection of packing plants had been carried out on the previous day, and residual contamination was found on 6.9% of samples from grading tables, 16.0% holding/sorting tables, 12.6% of conveyors or rollers, 16.7% of vacuum egg lifters, 21.4% of floor surfaces and 5.0% of egg store floor surfaces. Sterilized eggs passed through five farm packing plants showed a contamination rate of at least 16/5948 (0.3%) egg passages. Conclusions: It is apparent that contamination in egg-packing plants may be a significant contributory factor to external contamination of shell eggs, and improved methods of cleaning and disinfecting egg-handling equipment are required. Significance and Impact of the Study: The presence of Salmonella contamination in egg-packing plants presents a contamination hazard for eggs from Salmonella -free flocks. Samples from equipment in the packing plant could also be used for screening for detection of Salmonella in the throughout of the plant.