Abstract
Bovine salmonellosis is a worldwide bacterial disease causing great animal losses, public health and economical problems. The present study was conducted on a total number of 160 animals (130 calves and 30 adult cattle) at Alexandria governorate either individually or in farms. Out of them, 85 calves and 15 adult cattle were suffering from diarrhea while the remaining calves and adult cattle were apparently clinically healthy, rectal swabs and fresh fecal samples were collected and examined bacteriologically for the presence of Salmonella spp. The results revealed the isolation of Salmonella organism from 11 (13%) and 1 (6.6%) diarrheic calves and adult cattle, respectively, on contrary, no Salmonella could be isolated from all apparently clinically healthy animals. The 12 Salmonella isolates were examined for antimicrobial sensitivity using 10 antibiotic discs; all 12 (100%) isolates showed resistance to at least one antimicrobial, the highest resistance observed for erythromycin 12 (100%), tetracycline 8 (67%) and ampicillin 7 (58%) while the highest sensitivity was observed for streptomycin 10 (80%), gentamycin 9 (75%) and chloramphenicol 7 (58%). Conventional PCR performed on 10 Salmonella isolates for the presence of three virulence genes: invasion gene (invA), enterotoxin gene (stn) and plasmid encoded fimbriae gene (pefA); invA gene was detected in 7 (70%) isolates while stn gene was detected only in 2 (20%) isolates, but pefA gene could not be detected in all 10 Salmonella isolates. In a conclusion, Salmonella is one of the most important causes of diarrhea in calves and adult cattle, Salmonella isolates were resistant to most commonly used antibiotics resulting in difficulties in their treatment and the application of PCR assay is important for rapid detection of virulence profile of Salmonella.

Key words: Salmonella – Cattle – diarrhea – PCR – Virulence genes.