Effect of Stored Pre-Poured Plates on Microbial Enumeration Using the Surface Plate Method ¹.

Area of Science:

• Microbiology
• Food Science
• Analytical Chemistry

Background:

• Accurate enumeration of microorganisms is crucial for food safety and quality control.
• Traditional methods like pour plate and surface plate techniques are widely used.
• The impact of pre-poured agar plate storage on microbial recovery requires thorough investigation.

Purpose of the Study:

• To compare the efficacy of the surface plate method versus the pour plate method for enumerating microorganisms.
• To evaluate the effect of storing pre-poured agar plates on microbial recovery.
• To assess the reliability of these methods across various food matrices and bacterial species.

Main Methods:

• Comparison of surface plate and pour plate methods for microbial enumeration.
• Use of freshly prepared and stored pre-poured Plate Count Agar (PCA) plates.
• Testing on fresh bologna, ground beef, frozen turkey pot pie, and bacterial suspensions (Pseudomonas fluorescens, Streptococcus faecalis).
• Incubation of plates at 35°C for 48 hours, 20°C for 5 days, and 7°C for 10 days.

Main Results:

• Differences in microbial counts between methods were consistently less than 0.5 log cycle in 97% of comparisons.
• Highly significant regression (0.977–1.068) and correlation (0.987–0.999) coefficients were observed between methods.
• Storage of pre-poured plates at 5°C for up to 6 weeks showed no significant impact on microorganism recovery using the surface plate technique.

Conclusions:

• The surface plate method is a reliable alternative to the pour plate method for microbial enumeration in diverse food samples.
• Pre-poured agar plates can be stored for up to 6 weeks without compromising their performance in microbial recovery.
• These findings support the use of stored pre-poured plates, offering potential for improved laboratory efficiency and cost-effectiveness.