Clinical isolates of two positive-Gram (Bacillus cereus and Lis-teria monocytogenes) and two negative-Gram (Proteus vulgaris and Salmonella typhimurium) bacteria strains obtained from Microbiology Laboratory, Veterinary Medicine Faculty (I.A.U.), Iran. Bacterias trains were identified using polymerase chain reaction–restriction fragment length polymorphism (PCR–RFLP) and conventional morphological as well as biochemical tests.