The implementation of Food Safety Management Systems (FSMS) is crucial for preventing foodborne diseases. This study aimed to assess the performance of FSMS by detecting coliforms and Escherichia coli as indicators of foodborne pathogens in hamburger samples and evaluating the main sources of contamination in the final products. Three meat processing plants (A, B, and C) that implemented FSMS were evaluated based on prerequisite program (PRP) parameters in an observational study. A total of 107 samples were collected from raw materials, food handlers' hands, contact surfaces of food processing equipment, and products from the three plants. Additionally, 45 hamburgers were purchased from local markets in Tehran. Polymerase chain reaction analysis was conducted on the positive samples to confirm the presence of Escherichia coli O157:H7. The data were described using frequency (percentage) and mean (standard deviation), and a significance level of 5% was considered. Results showed that approximately 38% (41.107) of samples from the three plants were contaminated with coliforms and E. coli, with only one sample contaminated with E. coli O157:H7 from raw meat in plant C. Moreover, 80% (36.45) of hamburger samples collected from local markets contained coliforms lower than 102 CFU/g and E. coli lower than 10 CFU/g, with no contamination of E. coli O157:H7. The study found significant differences in the number of coliforms and E. coli among the three factories (p<0.05), with factory C having the highest and factory B having the lowest values. Implementation of FSMS in the food chain resulted in reduced microbial contamination. The study concluded that there is no safety concern regarding E. coli O157:H7 contamination in hamburgers marketed in Tehran.