Advanced Studies on Virulence Genes of Salmonella and Shigella species Isolated from Milk and Dairy Products

Abstract

Salmonella and Shigella species are the main health problem in various portions of the world. This study gave rise to detect and enumerate Salmonella and Shigella species with detection of virulence genes by PCR in randomly collected raw milk and dairy products (ice cream, cheese, yoghurt, rice with milk and cream) from different vendors of village and dairy farms in Mansoura Governorate, Egypt during October 2016. A total of 24 (9.6 %) isolates from 250 samples (raw milk and dairy products) were recognised as Salmonella6.4 % (16/250) and Shigella 3.2 % (8/250) species with their high prevalence in raw milk. Amongst serotypes of Salmonella species: S. Typhimurium 37.5 % (6/16), S. Enteritidis, S. Tsevie 18.75 % (3/16 each) and other serovars 25 % (4/16). Additionally, the identified Shigella species (8/250) were S. dysenteriae 50 % (4/8), S. flexneri 25 % (2/8) and S. sonnei 25 % (2/8). The average of total viable count of samples positive for Salmonella and Shigella in raw milk and dairy products was 4.47±0.97 log10 CFU/ml or gm and 4.27±1.01 log10 CFU/ml or gm, respectively.  Furthermore, polymerase chain reaction assay was applied for demonstration of the most common virulence associated genes of Salmonella species (invA) and Shigellaspecies (invC, ipaH, virA). The invA gene was present in all tested Salmonella isolates. The invC and ipaHgenes were present in all Shigella isolates, while virA gene was absent in all strains. This study recommended that appropriate hygienic measures, as well as continuous monitoring of Salmonella and Shigella infection, could help to control and prevent the emergence and spread of salmonellosis and shigellosis from milk and dairy products in Egypt.