Multidrug-resistant human mycobacterium tuberculosis strain resisted inactivation by 10% formalin

Area of Science:

• Microbiology
• Infectious Diseases
• Pathology

Background:

• Multidrug-resistant tuberculosis (MDR-Tb) poses a significant global health threat.
• Effective inactivation of Mycobacterium tuberculosis strains in biological samples is critical for laboratory safety and accurate diagnostics.

Purpose of the Study:

• To evaluate the efficacy of different tissue fixation methods for inactivating both multidrug-sensitive (MDS-Tb) and multidrug-resistant (MDR-Tb) strains of Mycobacterium tuberculosis.
• To determine the optimal preservation technique to ensure safety when handling potentially viable MDR-Tb in clinical or research specimens.

Main Methods:

• Guinea pigs were infected with either MDR-Tb or MDS-Tb strains.
• Infected lung tissues were subjected to two fixation protocols: 10% formalin alone, or a 2-hour pretreatment with 75% ethanol followed by 10% formalin fixation.
• Viability of Mycobacterium tuberculosis strains was assessed after six months of fixation.

Main Results:

• Both fixation methods completely inactivated MDS-Tb strains after six months.
• MDR-Tb strains remained viable in tissue fixed with 10% formalin only.
• Pretreatment with 75% ethanol prior to formalin fixation effectively inactivated MDR-Tb strains.
• A small percentage of human patients (8%) harbored MDR-Tb.

Conclusions:

• Standard 10% formalin fixation is insufficient for inactivating MDR-Tb in tissue samples.
• Pre-treating tissue with 75% ethanol before formalin fixation provides a necessary safety measure against viable MDR-Tb.
• Enhanced biosafety protocols are essential when dealing with tuberculosis specimens, particularly those potentially containing MDR strains.