Abstract

Bulk tank milk analysis was referred to as a useful and appropriate diagnostic tool to evaluate milk quality and mastitis pathogens in cattle dairy herds. Out of the total number of 150 pooled tank milk samples collected from 150 cattle dairy farms, 13 locally field Staphylococcus aureus isolates were detected and confirmed phenotypically by culturing, gram staining, biochemical, and molecular identification to be Staphylococcus aureus in the overall herd by the prevalence of 8.6%. Isolation and identification of Salmonella Typhimurium field isolates from bulk tank milk samples revealed that 20 locally field isolates were detected and confirmed phenotypically by culturing, gram staining, biochemical and molecular identification to be Salmonella Typhimurium in the overall herd by the prevalence of 13.3%. The results of total bacterial plate count (cfu/ml) revealed that the geometric mean of 150 dairy farms was 3.2×108 cfu/ml. The geometric mean of somatic cell count (SCC)/ml in Bulk tank milk samples of 150 cattle dairy farms were 556.7×103. The geometric mean value of Staphylococcus aureus count in this study was 3.7×103 cfu/ml. Serological identification of the 20 isolates revealed that they were Salmonella Typhimurium. The study provided various risk factors that had a clear and effective role in determining the level of Salmonella Typhimurium, Staphylococcus aureus, Standard plate count, and Somatic cell count in bulk tank milk. The PCR amplification with (hlg) gene-specific primers revealed a product with an approximate size of 937 bp. (hlg) gene found in 13 (54%) Staphylococcus aureus isolates. The PCR identification of sopB (SigD) virulence gene for Salmonella Typhimuriym revealed a product with an approximate size of 517 bp. SopB gene found in all Salmonella Typhimurium isolates (100%). Phylogenetic and partial gene sequence analysis of (hlg) Staphylococcus aureus gene of Egyptian isolated strain showed a great identity with the different Staphylococcus aureus strains uploaded from the gene bank. Phylogenetic analysis of Salmonella Typhimurium (sopB) virulence gene of Egyptian isolated strain indicated a great homology with the different Salmonella Typhimurium strains uploaded from the gene banks. The results of the present study emphasize the importance of more efficacious preventive programs for controlling the mastitis and bacteriological quality of bulk tank milk and monitoring mastitis economic losses.