การหาค่าความไม่แน่นอนของการวัดเชิงเทคนิคและการทวนสอบวิธีการตรวจสอบ ปริมาณโคลิฟอร์มด้วยวิธี Multiple Tube Fermentation ในตัวอย่างน้ำบริโภค ในภาชนะบรรจุที่ปิดสนิท น้ำแข็ง และน้ำดิบ

Denchai wongsrikeaw; Mantana Jamklang; Chompunoot wangboon; ‪Pongpat  Kiatprasert; Watsana Penkhrue

doi:10.60136/bas.v15.2026.4074

Authors

Denchai wongsrikeaw School of Preclinical Sciences, Institute of Science, Suranaree University of Technology, 111 University Avenue, Muang, Nakhon Ratchasima 30000, Thailand
Mantana Jamklang School of Preclinical Sciences, Institute of Science, Suranaree University of Technology, 111 University Avenue, Muang, Nakhon Ratchasima 30000, Thailand https://orcid.org/0000-0002-5657-4156
Chompunoot wangboon School of Preclinical Sciences, Institute of Science, Suranaree University of Technology, 111 University Avenue, Muang, Nakhon Ratchasima 30000, Thailand
‪Pongpat Kiatprasert Analytical Laboratory Centre, Faculty of Agriculture and Technology, Rajamangala University of Technology Isan, Surin Campus, 145 Nok Mueang, Mueang Surin 32000, Thailand
Watsana Penkhrue School of Preclinical Sciences, Institute of Science, Suranaree University of Technology, 111 University Avenue, Muang, Nakhon Ratchasima 30000, Thailand https://orcid.org/0000-0002-0009-5455

DOI:

https://doi.org/10.60136/bas.v15.2026.4074

Keywords:

Verification ISO 16140, Intralaboratory reproducibility standard deviation, Estimated bias (eBias)

Abstract

Coliform bacteria are a group of microorganisms commonly used as bacteriological indicators for assessing the microbiological quality and hygiene of water and food products. However, most laboratories in Thailand still lack verification data for microbiological analytical methods in accordance with ISO 16140-3:2021, which is essential for enhancing laboratory competence and supporting ISO/IEC 17025 accreditation. The determination of the Standard Deviation for Intralaboratory Reproducibility (S_IR) and the method verification serves as definitive evidence that a laboratory can competently perform reference methods to ensure accurate and reliable results for clients. This study aimed to evaluate laboratory capability in quantifying coliform bacteria across various water samples, including bottled drinking water, ice, raw water, food-contact surface water, and deionized (DI) water. The evaluation determined the S_IR and the Estimated bias (eBias) using the Multiple Tube Fermentation (MTF) method based on ISO 16140-3:2021 protocol for the verification of reference methods in a single laboratory. Three inoculation levels were evaluated: low (1 cfu/mL), medium (10 cfu/mL), and high (20 cfu/mL). The results revealed an overall S_IR of 0.14. The eBias values for Group (A) samples were 0.00, 0.30, and 0.05 Log₁₀ MPN/100 mL; for Group (B) samples were 0.18, 0.01, and 0.02 Log₁₀ MPN/100 mL; and for Group (C) samples were 0.12, 0.06, and 0.05 Log₁₀ MPN/100 mL, respectively. The method verification demonstrated that both S_IR and the eBias values across all water types complied with the acceptability limit of ≤0.5 Log₁₀ MPN/100 mL specified by ISO 16140-3:2021. This confirms that the laboratory can successfully implement the MTF method according to APHA, AWWA, and WEF standards with high accuracy and reliability. Consequently, these findings support the laboratory's application for ISO/IEC 17025:2017 accreditation and demonstrate that this verified MTF technique is highly suitable for drinking water quality surveillance systems to protect public health.

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