MYCOBACTERIUM

These are rod-shaped organisms which don't stain well with the Gram stain because of their thick waxy coat. An acid-fast stain such as the Zeihl-Neelsen stain is used instead heance the term acid-fast bacilli.
This picture is of acid-fast bacilli in a Zeihl-Neelsen stain of sputum.
It shows the typical shape of Mycobacterium tuberculosis. The many other species of mycobacteria are often referred to as 'atypical' because most of them have a slightly different shape.

Disease

- tuberculosis is caused by M. tuberculosis
- atypical mycobacterial infections

• a variety of diseases including pulmonary, cutaneous, disseminated and systemic disease
• caused by a number of different species of mycobacteria which are common in the environment in water, soil and dust
• disease is rare in immunocompetent individuals

Mode of transmission

TB is usually transmitted by exposure to organisms in aerosols produced during coughing and sneezing.
Atypical mycobacteria are acquired from the environment.

Significance in endoscopy

The Centres for Disease Control and Prevention recommend that bronchoscopy should not be performed on patients with active TB unless absolutley necessary.
Bronchoscopy should not be regarded as a first line investigation in the diagnosis of TB and repeated sputum smears should be negative for acid-fast bacilli before bronchoscopy is considered.
Mycobacteria are relatively resistant to most chemical agents including aldehydes. Atypical mycobacteria are even more resistant and tehre are reports of atypical mycobacteria that are totally resistant to glutaraldehyde.
A further disturbing development in the mycobacterial area is the appearance of multidrug-resistant tuberculosis.
There is no proven case of transmission of tuberculosis by gastrointestinal endoscopy. Numerous reports of mycobacterial transmission by flexible bronchoscopy, however, have been reported. Mycobacterial infections due to bronchoscopy have been related to:

• contaminated suction valves
• cracked biopsy channels
• contaminated topical anaesthetic solutions
• contaminated disinfecting machines

Epidemics of pseudoinfection associated with contaminated disinfecting machines have also been a cause of considerable confusion. The presence of atypical mycobacteria in bronchoscopes can also potentially contaminate specimens collected at bronchoscopy with acid-fast bacilli, which can result in a false diagnosis of TB.
Meticulous detailed mechanical cleaning by staff properly trained in bronchoscope reprocessing remains the best and indeed probably the only defence against transmission of mycobacterial disease by flexible bronchoscopy. It has been unequivocally demonstrated that even extremely prolonged bronchoscope immersion in 2% glutaraldehyde will not prevent disease transmission in inadequately cleaned instruments and accessories.
Atypical mycobacteria are frequently present in tap water. Rinsing of bronchoscopes after disinfection should be with sterile/filtered water. It is still critical that air/alcohol drying should be performed at the end of lists.
 source : http://www.health.qld.gov.au/EndoscopeReprocessing/module_1/1_3d.asp#Cdiff

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