Tehran University of Medical Sciences Journal of Medical Bacteriology 2251-8649 5 1-2 2016 12 31 52 54 EN Mohammad Sadegh Madadi Faculty of Veterinary Medicine, University of Tabriz, Tabriz, Iran. Mohammad Hassanzadeh Faculty of Veterinary Medicine, University of Tehran, Tehran, Iran. Fateme Karimnezhad Department of Food Hygiene, Science and Research Branch, Islamic Azad University, Tehran, Iran. 2016 12 31 2016 12 31 Background:  Young chickens are more susceptible to Salmonella colonization than older ones that have developed resistance with age as native microflora become established. Methods:  In this study, two groups of fertile eggs were inoculated with 20 CFU of hilA or parent strains of S. enteritidis. Presence and number of Salmonella cells inside the homogenized egg contents were determined on the 2nd, 5th, 8th, 12th, 17th and 21th day of incubation period. Results:   High infectivity rate of Salmonella contamination were observed in the hilA group eggs, three genes for S. enteritidis identification were detected from isolated colonies of both groups of eggs.  The gene hilA was only detected in isolated colonies of the standard group.  Conclusion:   These findings indicated that hilA mutant of Salmonella is able to rapidly multiply much higher than wild-type strain but, support more pathogenicity of wild-type strain of Salmonella compared to mutant strain. https://jmb.tums.ac.ir/index.php/jmb/article/view/232 https://jmb.tums.ac.ir/index.php/jmb/article/download/232/166