The effect of cleaning solution residues on microbiological testing

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เมธี ศรีประพันธ์
นันทวรรณ จินากุล


Objective: To compare the effect of glassware cleaning solution residues and the different rinsing procedures on microbial testing in microbiology laboratory.

Materials and Methods: The 2.0% glassware-washing solution for laboratory purpose (reagent type A) composing of polyethylene glycol dodecyl and ethylene oxide, 2.0% dish-washing reagent (reagent type B) composing of linear alkylbenzene sulfonate,  potassium salt and sodium lauryl ether sulfate, and 0.5% detergent (reagent type C) composing of anionic surfactant, zeolite, sodium carbonate, sodium carboxymethyl and cellulose were used to evaluate the detergent residues after performing 5 different rinsing procedures (No rinsing, rinsing for 1, 3, 6 and 12 times) on petri dishes. Sterile glass petri dishes were included as negative control. The pH of cleaning residue was determined using 0.04% Bromthymol blue. The 50-100 CFU/mL of Staphylococcus aureus (ATCC 6538) was used to explore the efficiency of bacterial growth on glass petri dishes with pour plate method and reported as mean CFU/mL with standard error of the mean (SEM). Statistical analysis was performed with either IBMÒ SPSSÒ version 23 or GraphPad PrismÒ version 6.01. The p-value < 0.05 indicated statistical significant at 95% confident interval.    

Results: The reagent type A was alkaline and became neutral after rinsing for 3 times. Additionally, the reagent type B was acidic and turned into neutral after rinsing for 3 times. Moreover, the reagent type C was alkaline and became neutral after rinsing for 6 times. All 3 detergents affect microbial growth at statistically significant level (p < 0.05) in the conditions of no rinsing, rinsing for 1, 3 and 6 times. Using reagent type A or B following by rinsing for 3 times did not show statistically significant in bacterial growth (p > 0.05). However, the bacterial growth was not significant different in the use of reagent type C comparing with reagent type A or B. When considering the rinsing procedures less significantly affecting bacterial growth         (p > 0.05), the suggested protocols for using reagent type A or  was 3-12 times whereas the protocol for reagent type B was 6-12 times and the protocol for reagent type C was 12 times.

Conclusion: Each cleaning solution has different pH properties in detergent residues, which is solved by rinsing protocols.  Moreover, different types of detergent and rinsing procedures significantly affect the bacterial growth. The suitable protocols for each washing solution are rinsing at least 3 time for 2.0% glassware-washing solution, rinsing at least 6 times for 2.0% dish-washing reagent and rinsing at least 12 times for 0.5% detergent, respectively.



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