MIDI Sherlock Microbial Identification System Operating Manual

Significance of Microbial Fatty Acid Analysis

Microbial identification by fatty acid methyl ester (FAME) profiling offers a rapid and reproducible approach for microbial speciation across clinical, environmental, industrial, and QA/QC laboratories.

System Overview and Instrumentation

The Sherlock Microbial Identification System integrates standardized sample preparation with an Agilent 6890/6850/7890 GC, automatic liquid sampler, and ChemStation-driven data processing. Automated calibration and quality control routines ensure consistent retention time precision and quantitative accuracy.

Sample Preparation Protocol

Samples are grown under defined conditions, harvested from late-log-phase cultures, and processed through four reagent steps: saponification, methylation (acidified methanol), liquid–liquid extraction (hexane/MTBE), and base wash. Critical controls include a reagent blank and known strain QC to monitor reagent purity and instrument performance.

Software Workflow and Data Analysis

A computer-controlled Sample Processor logs sample IDs, injects extracts, and receives GC data from ChemStation. Automated batches run calibration standards and samples, calculating equivalent chain lengths (ECLs) for peak identification and performing library searches to assign similarity indices. The Sherlock CommandCenter archives data, generates reports, and manages methods and libraries.

Maintenance and Troubleshooting

Routine upkeep includes replacing septa and injection port liners, monitoring hydroxy-FAME recovery via PQ tables, and recalibrating column pressure and oven temperature. Common issues such as peak tailing, baseline noise, and poor hydroxy recovery are addressed through injector component replacement, gas purity checks, and column conditioning or replacement.

Future Trends and Applications

Advances may include integration of AI-driven pattern recognition, expansion of libraries to new microbial taxa, miniaturized extraction formats, and high-throughput automation for environmental and clinical real-time monitoring.

Conclusion

The Sherlock MIS provides a robust, high-throughput platform for microbial identification based on fatty acid profiling. Adherence to standardized protocols and proactive maintenance ensures reliable, reproducible results across diverse microbiological workflows.

References

Manufacturers’ manuals for MIDI Sherlock MIS and Agilent GC systems. Current MIDI reagent and library guides.