Swab test of E. Coli cells

Significance of the Topic

The ability to detect and quantify microbial contamination on production equipment is essential in pharmaceutical cleaning validation. Swab testing for Escherichia coli cells using total organic carbon (TOC) solid-sample analysis offers a rapid, sensitive measure of residual cells and organic residues, improving quality control and process verification.

Objectives and Overview of the Study

This application note demonstrates a direct swab method for measuring E. coli cell contamination on stainless-steel surfaces. Key goals include evaluating TOC solid-sample analysis performance, assessing recovery rates, and establishing quantitation limits in the context of cleaning validation.

Methodology and Instrumentation

Samples of controlled E. coli suspensions were deposited on steel Petri dishes, wiped using carbon-free swabs, then analyzed directly without extraction. The procedure employed Shimadzu’s TOC-V series analyzer coupled with an SSM-5000A solid sample module and ASI-V autosampler. Swabs were combusted at 900 –980 °C with an oxidation catalyst. Evolved CO2 was measured by a tandem-cell non-dispersive infrared (NDIR) detector. Calibration used diluted glucose standards (10–100 µg C) added incrementally to a ceramic sample boat.

Used Instrumentation

• Shimadzu TOC-V CSH analyzer
• Shimadzu ASI-V autosampler
• Shimadzu SSM-5000A solid sample module
• NDIR tandem detection cell
• Ceramic sample boats and quartz fiber swabs
• Ultrapure water and oxidation catalyst

Main Results and Discussion

Calibration showed linear response for 10–100 µg carbon with coefficient slopes consistent for solid samples. Blank swabs contributed an average of 9 µg C. Quantitative swab tests on E. coli-spiked dishes yielded TOC increases proportional to cell counts (8 × 106 to 3.3 × 107 cells). Regression slopes for swab measurements closely matched those for control solutions, confirming reproducibility and accuracy. Data indicate reliable detection of bacterial contamination in under 5 minutes per sample.

Benefits and Practical Applications of the Method

This direct swab-TOC approach enables rapid screening of hard-to-access equipment areas, edges, and corners without laborious extraction. With minimal sample preparation and total analysis times of around 4 minutes, it supports efficient cleaning validation workflows in pharmaceutical and biopharmaceutical manufacturing. The method’s flexibility allows switching between liquid and solid sample modes.

Future Trends and Potential Applications

Advances may include automated swab handling, improved swab materials with lower blank contributions, and integration with laboratory information management systems. Extending the approach to other microbial or organic contaminants could broaden its role in hygiene monitoring, environmental testing, and validation of single-use systems.

Conclusion

The direct solid-sample TOC swab test using Shimadzu’s TOC-V/SSM-5000A platform provides a robust, fast, and quantitative tool for E. coli contamination assessment. Its high sensitivity, reproducibility, and simple operation make it well suited for routine cleaning validation and quality assurance in regulated environments.