Inoculating guinea pigs with BCG strains resulted in abscesses at the injection site, with a higher occurrence (92.8%) from the classical strain compared to the INH-resistant strain (23.5%).
The abscesses from the classical strain were more persistent, lasting over a year, while those from the INH-resistant strain typically regressed within six months.
Histological analysis showed that the abscesses' structure changed over time, with recent abscesses being larger and more infectious than older ones, indicating that the INH-resistant strain is less aggressive and eliminated more quickly than the classical strain.