Uncertainty of Total Bacterial Count in Food by the Pour Plate Technique of the Microbiological Laboratory, Regional Medical Sciences Centre 10, Ubonratchathani

Abstract

Background: Total Bacterial Count Analysis is a standard criterion to indicate food spoilage. If the amount of Total Bacterial Count is high, it causes many diseases especially in the children who get low immunities; such as, stomachache, nauseous, vomit, and fever. The Ministry of Public Health that is specified in many types of food. The microbiological laboratory Medical Sciences Center 10, Ubon Ratchathani analyzed samples using the BAM Online. Chapter 3. 2001 with Pour plate technique. The standard required laboratories to evaluate measurement uncertainty to show the accuracy from ISO 19036:2009 standards. The standard required laboratories to evaluate measurement uncertainty to show only deviation standard of reproduction. Since the standard ISO 19036:2019 in the new version required Pour plate technique, it obtained to calculate the 3 uncertainty components; Technical uncertainty, Matrix uncertainty, and Distribution uncertainty. Thus, the microbiological laboratory Medical Sciences Center 10, Ubon Ratchathani had to indicate the uncertainty concerning with the standard in the present time.

Objectives: This research was aimed to evaluate the results of Intralaboratory reproducibility standard deviation (S_IR), and to calculate the expanded uncertainty analysis’s result

Methods: This experimental research was in The microbiological laboratory Medical Sciences Center 10, Ubon Ratchathani during August-October, 2020. There were 4 analyzers in the laboratory analyzed of total bacteria count in food with 10 different samples by using the BAM Online (2001) Chapter 3 standard method. The samples were Vietnamese noodles, milk, prickled fish, sauces, ingredient powder, ice-cream, sausages, Isan pricked pork, sushi, and others with lyophilize sample. Then, the results were calculated from Standard deviation, S_IR or Technical Uncertainty (U_tech) referred to uncertainty of procedure analysis in the microbiology laboratories; Matrix Uncertainty (u_matrix) referred to uncertainty of the samples’ characteristics and bacteria’s spreading in the samples; and Distributional Uncertainty (u_poisson) referred to uncertainty of total colonies counting analysis to the results’ report.

Results:  Based on the analysis of total bacteria count in 10 different food samples from 4 analyzers and covered in normal, routine and naturally contaminated samples that the estimated results were not different in statistical significance (p-value) = 0.9989. The standard deviation of reproducibility (S_IR) value was 0.0946. This was used to calculate the expanded uncertainty for the report on the total bacterial counts in food  to show the extent of the error of the results at the 95% confidence level.

Conclusions: The results of uncertainty estimation from intralaboratory reproducibility standard deviation (S_IR) appropriated to find the results of the uncertainty of the total bacterial count in the sampling food. However, the laboratory should experiment the other kinds of food to test or aware in S_IR value which should not higher than the laboratory’s limitation with 0.1 value. If higher, the laboratory should analyze other factors, and improve in the case of changing the analyzers with the new up-to-date S_IR value.