PCR amplification of invA

All the MDR Salmonella spp. were tested for the presence of the virulence gene invA [26,27]. This gene is responsible for the virulence factor of Salmonella spp. The specific primers used to detect invA in Salmonella isolates have been previously published [16], which included the forward primer $\acute{5}$ GTG AAA TTA TCG CCA CGT TCG GGC AA $\acute{3}$ and the reverse primer $\acute{5}$ TCA TCG CAC CGT CAA AGG AAC C $\acute{3}$ (284 bp). This study was conducted at the Veterinary Public Health Laboratory, Faculty of Veterinary Medicine, Universitas Airlangga, and the Microbiology Laboratory of the Central Health Laboratory, Surabaya. In the PCR analysis, Escherichia coli isolate ATCC 25922 was used as a negative control, and Salmonella Paratyphi A isolate ATCC 9150 was used as a positive control, which had been previously tested for the presence of invA.