Rapid identification of laboratory contamination with Mycobacterium tuberculosis using variable number tandem repeat...

Area of Science:

• Microbiology
• Molecular Diagnostics
• Infectious Disease Epidemiology

Background:

• Broth-based mycobacterial culture systems offer high sensitivity but are prone to cross-contamination, leading to false positives.
• Systematic strain typing is often avoided due to technical complexity and data management challenges.
• Variable number tandem repeat (VNTR) analysis presents a rapid, reproducible molecular method for strain typing.

Purpose of the Study:

• To evaluate the utility of VNTR analysis in identifying cross-contamination events in a BACTEC MGIT 960 system.
• To assess the impact of cross-contamination on false-positive tuberculosis diagnoses.
• To determine if VNTR analysis can improve patient management by preventing unnecessary treatment.

Main Methods:

• Retrospective study of Mycobacterium tuberculosis isolates over 18 months.
• VNTR allele profiling of early positive broth cultures.
• Integration of VNTR profiles with specimen processing dates and clinical data into a database.

Main Results:

• Identified 36 distinct VNTR profiles among 144 patients.
• Three common VNTR profiles represented 45% of true-positive cases.
• Discovered nine cross-contamination incidents, six previously unsuspected, leading to 34 false-positive cultures for 29 patients.

Conclusions:

• VNTR analysis, when combined with specimen data, is a powerful tool for detecting cross-contamination in mycobacterial cultures.
• Molecular methods like VNTR analysis should supplement automated broth culture systems to ensure accurate diagnoses.
• Timely identification of false positives prevents inappropriate tuberculosis therapy and aids in process improvement.