MYCOBACTERIUM TERRAE - A POTENTIAL SURROGATE FOR MYCOBACTERIUM-TUBERCULOSIS IN A STANDARD DISINFECTANT TEST

The susceptibility of Mycobacterium tuberculosis and Mycobacterium avi um-intracellulare to the disinfectants used for spillage and heat sens itive instruments has received much attention in recent years. The use of clinical isolates of M. tuberculosis and M. avium-intracellulare a s test organisms is considered unsuitable for standard tests due to th eir hazardous nature (category 3 pathogens and slow growth rates). Thi s has led to much debate in standards committees on the selection and use of a possible surrogate which would be safer and more practical to use and yet mimic the susceptibility of clinical isolates. This study compared the susceptibility of one possible surrogate Mycobacterium t errae NCTC 10856, with that of clinical isolates of M. tuberculosis H3 7 Rv and M. avium-intracellulare, using a quantitative suspension test . The instrument and environmental disinfectants tested were a chlorin e-releasing agent, sodium dichloro-isocyanyurate (NaDCC) at 1000ppm an d 10000ppm av. Cl, chlorine dioxide at 1100 ppm av. ClO2 (Tristel, Hay Man MediChem), 0.35% peracetic acid (NuCidex, Johnson & Johnson), 70% industrial methylated spirit (IMS), 2% alkaline glutaraldehyde (Asep, Galen), 10% succine dialdehyde and formaldehyde mixture (Gigasept, Sch ulke and Mayr). Results showed that the clinical isolate of M. avium-i ntracellulare was the most resistant of the three test organisms. M. t errae, which is not a category 3 pathogen, was slightly more resistant than M. tuberculosis and this would appear to be a suitable surrogate for establishing tuberculocidal activity. However, with an increase i n the clinical significance of M. avium-intracellulare, , particularly in human immunodeficiency virus (HIV) and immunocompromised patients, a more resistant surrogate is required. In the absence of such a surr ogate, testing with M. avium-intracellulare in a clinical laboratory e quipped for handling category 3 pathogens is still advised to establis h mycobactericidal activity.