Salmonella Enteritidis is a common foodborne pathogen transmitted to humans largely by consumption of contaminated eggs, according to Indu Upadhyaya and colleagues at the University of Connecticut.

In a paper in the current issue of Poultry Science, they explain that the external surface of eggs becomes contaminated with Salmonella Enteritidis from various sources on farms, the main sources being hens’ droppings and contaminated litter. Therefore, effective egg surface disinfection is critical to reduce pathogens on eggs and potentially control egg-borne disease outbreaks.

Their study investigated the efficacy of GRAS (generally recognised as safe) status, plant-derived antimicrobials (PDA), namely trans-cinnamaldehyde (TC), carvacrol (CR) and eugenol (EUG), as an antimicrobial wash for rapidly killing Salmonella Enteritidis on shell eggs in the presence or absence of chicken droppings.

White-shelled eggs inoculated with a five-strain mixture of nalidixic acid (NA)-resistant Salmonella Enteritidis (8.0 log cfu per mL) were washed in sterile deionised water containing each PDA (0.0, 0.25, 0.5 or 0.75 per cent) or chlorine (200mg per kg) at 32 or 42°C for 30 seconds, three minutes or five minutes.

Approximately 6.0 log cfu per mL of Salmonella Enteritidis was recovered from inoculated and unwashed eggs.

The wash water control and chlorine control decreased Salmonella Enteritidis on eggs by only 2.0 log cfu per mL, even after washing for five minutes.

The PDA were more effective in killing Salmonella Enteritidis on eggs than the controls (P<0.05). All treatments containing CR and EUG reduced Salmonella Enteritidis to undetectable levels as rapidly as within 30 econds of washing, whereas TC (0.75 per cent) completely inactivated Salmonella Enteritidis on eggs washed at 42°C for 30 seconds (P<0.05).

No Salmonella Enteritidis was detected in any PDA or chlorine wash solution; however, substantial pathogen populations (around 4.0 log cfu per mL) survived in the antibacterial-free control wash water (P<0.05).

The CR and EUG were also able to eliminate Salmonella Enteritidis on eggs to undetectable levels in the presence of three per cent chicken droppings at 32°C (P<0.05).

Upadhyaya and colleagues concluded that their results demonstrate PDA could effectively be used as a wash treatment to reduce Salmonella Enteritidis on shell eggs. They added that sensory and quality studies of PDA-washed eggs need to be conducted before recommending their use.

Reference

Upadhyaya I., A. Upadhyay, A. Kollanoor-Johny, S.A. Baskaran, S. Mooyottu, M.J. Darre and K. Venkitanarayanan. 2013. Rapid inactivation of Salmonella Enteritidis on shell eggs by plant-derived antimicrobials. Poult. Sci. 92(12):3228-3235. doi: 10.3382/ps.2013-03126