Background: Herbal products have been globally used for health promotion. These products were frequently contaminated with various microorganisms due to raw materials and unhygienic production process. Microbiological quality of several forms is necessary to determine by microbial contamination assay in order to assure the safety of Thai herbal products.
Objective: To investigate the microbiological quality of Thai herbal products commercially distributed from different regions of Thailand and marketed in Bangkok and Pathumthani province by bacterial contamination assay.
Material and Method: Thai herbal products were randomly collected in Bangkok and Pathum Thani province. Total of 94 samples were in different dosage forms including liquids, pills, capsules and powders. The samples were divided into two groups as Standard Certified and Non-Certified herbal products. The products were tested as plate count method using spread plate technique. The obtained results were interpreted based on Thai Herbal Pharmacopoeia.
Results: The total plate counts of Standard Certified samples were ranged between less than 30 to 5.8 x 107 cfu/g or ml and the Non-Certified samples were ranged between less than 30 and 6.0 x 106 cfu/g or ml. In addition, the results showed that 7 out of 49 (14.28%) of Standard Certified sample group and 5 out of 45 (11.11%) of the Non-Certified sample group were out of the range of acceptable standard. The finding indicated that the microbiological quality of both Standard Certified and Non-Certified Thai herbal products showed no significant differences.
Conclusion: Majority of the herbal products tested for bacterial contamination were in acceptable standard. However, some products were out of acceptable range. Hence the rigorous assessment of quality control and good manufactury practice of Thai herbal production is necessary for safe consumption.

Keywords: Bacterial contamination assay, Thai herbal products, Total plate counts, Standard Certified Thai herbal products, Non-Certified Thai herbal products