Pseudomonas pellicle in disinfectant testing: electron microscopy, pellicle removal, and effect on test results

Area of Science:

• Microbiology
• Analytical Chemistry
• Disinfectant Efficacy Testing

Background:

• Pseudomonas aeruginosa ATCC 15442 is essential for disinfectant efficacy testing.
• This bacterium forms a dense pellicle at the liquid-air interface when cultured.
• The pellicle's structure and impact on testing are not fully understood.

Purpose of the Study:

• To examine the structure of the Pseudomonas aeruginosa pellicle using scanning electron microscopy.
• To evaluate the effectiveness of three methods for removing the pellicle.
• To determine the influence of pellicle fragments on disinfectant efficacy test outcomes.

Main Methods:

• Scanning electron microscopy (SEM) was used to visualize pellicle structure.
• Pellicle removal efficacy was assessed by quantifying bacterial cell numbers on penicylinders after treatment (decanting, vacuum suction, filtration).
• The Association of Official Analytical Chemists (AOAC) use-dilution method was employed to evaluate the impact of pellicle fragments on disinfectant efficacy.

Main Results:

• SEM revealed the pellicle as a thick, dense network of interlacing Pseudomonas aeruginosa cells.
• No significant differences were found in the efficacy of the three pellicle removal methods.
• The presence of pellicle fragments in disinfectant efficacy tests led to a significant increase in positive results (indicating reduced efficacy).

Conclusions:

• The Pseudomonas aeruginosa pellicle is a robust biofilm structure.
• Standard pellicle removal methods do not significantly differ in effectiveness.
• Pellicle fragments can falsely elevate disinfectant efficacy test results, potentially compromising product safety assessments.