Microbial Source Tracking (MST) Analysis

Advanced Microbial Source Tracking (MST) Analysis Services – High‑Resolution Molecular Typing for Contamination Source Identification and Outbreak Investigation

The precise identification of the origin of microbial contamination is a critical challenge in food safety, public health, pharmaceutical manufacturing, and environmental monitoring. Microbial source tracking (MST) – also known as microbial溯源 or bacterial source tracking – employs a suite of powerful molecular typing techniques to compare and link microbial isolates, enabling the definitive identification of contamination sources, the tracing of transmission routes, and the confirmation of epidemiological relationships. Whether investigating a foodborne outbreak, verifying the cleanliness of a production line, or tracing a nosocomial infection, MST provides the actionable intelligence needed to implement targeted corrective actions and to prevent future occurrences. However, a successful MST analysis is not a single test; it is a systematic, multi‑tiered approach that integrates high‑resolution typing methods (PFGE, MLVA, MLST, SNP‑based WGS), advanced bioinformatics, and, crucially, the comparison of the generated fingerprints with comprehensive reference databases. A poorly designed or executed MST can lead to false linkages, missed sources, and erroneous conclusions, wasting resources and compromising public health. Our ISO/IEC 17025‑accredited and GMP‑compliant laboratory offers a fully integrated microbial source tracking platform, combining the gold‑standard Pulsed‑Field Gel Electrophoresis (PFGE) and Whole‑Genome Sequencing (WGS) with sophisticated bioinformatics pipelines, including core‑genome MLST (cgMLST), SNP phylogenomics, and plasmid/replicon typing. We deliver definitive, traceable source‑attribution reports, with full quality control, expert epidemiological interpretation, and actionable recommendations. Our experienced team ensures that you obtain the highest‑confidence linkage or exclusion data, enabling you to identify the root cause of contamination, to validate your control measures, and to protect your brand and your consumers.

1. The Scientific and Operational Rationale for Microbial Source Tracking

Microbial source tracking serves multiple critical purposes: (a) to identify the specific origin of a contamination event (e.g., a specific production line, a raw material supplier, or an environmental reservoir); (b) to confirm the epidemiological link between clinical cases and a suspected food or environmental source; (c) to validate the effectiveness of corrective actions by demonstrating that the source has been eliminated; (d) to monitor the persistence of endemic strains and to detect the introduction of new clones; (e) to support regulatory investigations and to provide defensible evidence for legal proceedings; and (f) to assess the genetic stability of production strains and to confirm their identity. The choice of typing method – whether PFGE (for rapid, high‑discrimination screening), MLST (for evolutionary lineage assignment), or WGS (for single‑nucleotide resolution) – must be guided by the required resolution, the urgency of the result, and the availability of reference databases. Our service begins with a comprehensive consultation to define the optimal MST strategy for your specific sample set, ensuring both scientific rigor and operational efficiency.

2. Our Comprehensive Microbial Source Tracking Platform – Multi‑Method, High‑Resolution

We maintain a complete suite of validated MST methods, all performed in a dedicated molecular epidemiology facility with stringent contamination controls, and with certified reference strains for method validation and daily quality assurance. Our portfolio includes:

2.1 Pulsed‑Field Gel Electrophoresis (PFGE) – The Gold‑Standard for Outbreak Screening
We perform the standardised PFGE protocol (including PulseNet guidelines) for a wide range of foodborne and clinical pathogens (Salmonella, E. coli, Listeria, Campylobacter, etc.). Using rare‑cutting enzymes (e.g., XbaI, SpeI, SmaI), we generate high‑resolution DNA fingerprints that can be compared directly to the > 500,000 patterns in the PulseNet international database. We provide a definitive assessment of strain relatedness, including the construction of a dendrogram and the calculation of Dice similarity coefficients, enabling rapid identification of a match.

2.2 Multi‑Locus Sequence Typing (MLST) – For Phylogenetic Lineage Assignment
We perform MLST by sequencing 7‑8 housekeeping genes (as per the PubMLST scheme) to assign a definitive sequence type (ST) to your isolate. This places the isolate in a global phylogenetic context and allows the identification of the clonal complex, providing a robust basis for understanding the evolutionary history of the strain. MLST is particularly valuable for confirming the identity of production strains and for long‑term surveillance.

2.3 Multi‑Locus Variable‑Number Tandem‑Repeat Analysis (MLVA) – Fine‑Scale Epidemiological Typing
We offer MLVA as a complementary method, particularly for organisms where PFGE may not provide sufficient discrimination (e.g., for certain serotypes of Salmonella). MLVA provides a highly discriminatory fingerprint based on the variation in the number of repeats at multiple loci, and it is often used for high‑resolution cluster analysis.

2.4 Whole‑Genome Sequencing (WGS) – Single‑Nucleotide Resolution for Definitive Source Attribution
We perform high‑quality WGS (Illumina, and, for complex genomes, hybrid with Nanopore/PacBio) to obtain the complete genomic sequence of your isolates. Our bioinformatics pipeline includes:

• Single‑nucleotide polymorphism (SNP) detection – using a reference‑based approach (e.g., GATK, Samtools) to identify all SNPs and indels, providing the ultimate level of discrimination between closely related strains.
• Core‑genome MLST (cgMLST) – using the core genome (typically > 90% of the coding sequences) to generate an allelic profile and a dendrogram with very high bootstrap support.
• Phylogenetic tree construction – using maximum‑likelihood (RAxML, IQ‑TREE) or Bayesian methods (BEAST) to reconstruct the evolutionary relationships and to infer the most likely transmission pathway.
• Plasmid and mobile genetic element analysis – to identify the presence of shared plasmids, which can be strong evidence of a common source.
• Resistome and virulome profiling – to characterise the genetic determinants that may be associated with the outbreak.

2.5 Database Comparison and Epidemiological Interpretation – PulseNet, NCBI, and Custom Databases
We compare your PFGE and WGS data with the PulseNet international database, the NCBI Pathogen Detection database, and, where available, with your own in‑house or custom databases. We provide a comprehensive report that includes: (a) the similarity of your isolate(s) to each other; (b) the relationship to any known outbreak clusters or reference strains; and (c) a clear statement on the likelihood of a common source.

2.6 Method Validation and Quality Control – Ensuring Reproducibility and Accuracy
We provide full method validation for your MST workflow, including: (a) the reproducibility of the fingerprints (for PFGE) or the variant calls (for WGS); (b) the discriminatory power (using the Simpson’s index of diversity); (c) the stability of the typing profile over time; and (d) the specificity of the method for the target organism. The validation report is structured to meet the requirements of regulatory submissions and internal quality assurance.

2.7 Rapid Outbreak Investigation – Expedited Turnaround for Critical Incidents
For urgent public health or product‑recovery events, we offer expedited MST services, with a focus on PFGE (24‑48 hour turnaround) and, if required, a preliminary WGS analysis (3‑5 days). We provide interim reports as soon as the data are available, and we maintain direct communication with your team to ensure that the results are immediately actionable.

3. Advanced Capabilities – Integration of Multiple Methods, Customised Databases, and Source Attribution Modelling

For clients requiring the highest level of confidence or facing complex, multi‑source contamination scenarios, we offer a suite of customised, research‑grade services that go beyond routine source tracking:

3.1 Multi‑Method Integration – Combining PFGE, MLST, and WGS for a Complete Picture
We can perform a triangulation of methods, combining PFGE (for rapid screening), MLST (for phylogenetic placement), and WGS (for definitive SNP‑level linkage). This integrated approach provides the highest confidence in the source attribution, and it is particularly valuable for legally sensitive investigations.

3.2 Custom Database Development – For Unique Organisms or Surveillance Programmes
If your organism is not represented in the public databases, or if you need a specialised database for your internal quality‑assurance programme, we can develop and populate a custom database with the fingerprints and genomes of your reference strains. We also provide the database maintenance and update services.

3.3 Plasmid and Mobile Element Tracking – For Horizontal Gene Transfer Studies
We specialise in the tracking of plasmid‑borne resistance and virulence genes. By analysing the plasmid profile (using WGS or plasmid‑specific PCR), we can determine whether two isolates share the same plasmid, which is strong evidence of a recent common source or of horizontal gene transfer.

3.4 Source Attribution Modelling – Quantitative Source Apportionment
Using the genomic data and, where appropriate, the epidemiological metadata, we can apply source attribution models (e.g., Bayesian source attribution) to estimate the most likely source of a contamination event, providing a quantitative estimate of the contribution of each potential source.

3.5 Longitudinal Stability Studies – Monitoring Strain Persistence and Evolution
We can perform longitudinal studies to track the genetic stability of a strain over time, by sampling the same strain at multiple time points and performing WGS or PFGE. This is essential for confirming that a persistent contamination is due to the same strain and not to repeated introductions.

3.6 Data Review and Regulatory Submission Support
Our team of experienced molecular epidemiologists and bioinformaticians can assist you in the interpretation of the MST data, in the preparation of the required documentation for regulatory submissions, and in responding to queries from authorities. We provide a full data package, including the raw fingerprints, the sequence data, the phylogenetic trees, and the attribution reports.

4. Data Integrity, Standardisation, and Comprehensive Reporting

All analyses are conducted under a strict quality management system that includes the use of certified reference strains, routine positive and negative controls, and participation in proficiency testing schemes (e.g., the PulseNet PT, or the UK NEQAS). Our reports provide:

• Full method description – detailing the typing methods used, the enzymes, the conditions, and the bioinformatics pipelines.
• Detailed results – including the PFGE fingerprints, the MLST profiles, the WGS variant tables, the phylogenetic trees, and the similarity coefficients.
• Source attribution statement – a clear, objective assessment of the relatedness of the isolates and the likelihood of a common source, based on the combined evidence.
• Quality control data – the results of the concurrent controls, confirming the validity of the test run.
• Interpretative comments – by our senior molecular epidemiologists, providing a context‑specific interpretation of the results and, where appropriate, recommendations for corrective actions or further investigations.

Our reports are structured to meet the requirements of regulatory audits, customer inspections, and internal quality assurance, and they are defensible in legal proceedings.

Turnaround times: 2‑3 working days for PFGE analysis, 3‑5 working days for MLST, 1‑2 weeks for WGS‑based MST, and 1‑2 weeks for integrated multi‑method studies. Express services are available for urgent outbreak investigations.

5. Why Choose Our Laboratory for Microbial Source Tracking

We are one of the few laboratories that hold ISO/IEC 17025 accreditation and GMP compliance for the full spectrum of MST methods, including PFGE, MLST, and WGS‑based phylogenomics, for a wide range of bacterial and fungal pathogens. Our integrated infrastructure combines state‑of‑the‑art PFGE systems, high‑throughput sequencing platforms, and powerful bioinformatics pipelines with dedicated epidemiological analysis tools – enabling cross‑verification of results and a consistent, objective interpretation of the source‑attribution data. Our team comprises PhD‑level molecular biologists, bioinformaticians, and epidemiologists with extensive experience in method development, validation, and the interpretation of complex outbreak data, and we have a proven track record of supporting public health, food safety, and pharmaceutical quality‑control programmes.

We offer unparalleled flexibility: we accept all types of microbial isolates – from pure cultures, food, water, environmental samples, and clinical specimens – and we provide customised typing strategies to meet your specific organism, budget, and turnaround requirements. Our secure online portal enables real‑time tracking, access to raw data, and downloadable certificates of analysis.

Our modular pricing ensures cost‑effectiveness: you select the level of analysis – from a simple PFGE screening to a comprehensive WGS‑based source‑attribution study – with discounts for routine monitoring programmes and bulk submissions. We also provide training, method transfer, and technical consultancy to help you build or strengthen your internal MST capabilities.

With a proven history of serving over 90 clients in the food, pharmaceutical, and public health sectors, we have enabled our partners to identify the root cause of contamination, confirm source‑linkages, and implement effective corrective actions. We invite you to leverage our expertise for your microbial source tracking needs.

Contact our technical experts today to discuss your sample types, your investigative objectives, and your regulatory requirements. We will design a tailored source‑tracking plan and provide a detailed proposal within one business day.