Mycobacterium tuberculosis - Complications, Drug resistance, Latent TB, Treatment, AST, DST

Complications of Mycobacterium tuberculosis

Miliary disease, disseminated tuberculosis, and tuberculous meningitis caused by Mycobacterium tuberculosis are the most serious complication of primary complications of tuberculosis.

Pleural effusion and pneumothorax are other pulmonary complications of tuberculosis. Intestinal perforation, obstruction, and malabsorption are complications of tuberculosis of the small intestine. Hydronephrosis and auto nephrectomy are renal complications.

Paraplegia is the impairment in motor or sensory function of the lower extremities.

Mycobacterium tuberculosis with HIV

HIV patients with Mycobacterium tuberculosis are more likely to progress to disseminated disease. These patients usually do not have the cavitary pulmonary disease or upper lobe infiltrates in the lung.

Patients with tuberculosis should be tested for HIV and those with HIV need to be tested periodically for tuberculosis by tuberculin skin test and chest radiography. HIV patients with a positive tuberculin skin test usually develop active tuberculosis at a rate of 3-16% per year. HIV reactivates latent infection and makes the disease more serious and treatment ineffective.

The patient with both HIV and Mycobacterium tuberculosis on treatment with antiretroviral therapy develops various clinical manifestations which include fever, lymphadenopathy, and noninvasive pulmonary infiltrates.

Drug-resistant TB

With increasing resistance to antibiotics, Mycobacterium tuberculosis can be classified as:

1. Mono resistant => resistant to anyone TB treatment

2. Poly resistant => resistant to at least 2 TB drugs (but not both isoniazid and rifamycin)

3. MDR TB => is resistant to at least isoniazid and rifampin, the two best first-line TB treatment drugs

4. XDR TB => resistant to isoniazid and rifamycin, PLUS resistant to any fluoroquinolone and at least 1 of the 3 injectable 2nd like drugs (eg. amikacin, kanamycin, or capreomycin)

Treatment of Mycobacterium tuberculosis

The treatment of Mycobacterium tuberculosis is done by following methods:

• 1^st line drug: Isoniazid, rifampicin, pyraziramide, streptomycin, ethambutol

• 2^nd line drug: kanamycin, amikacin, ciprofloxacin, ofloxacin, cycloserine

• DOTS method is highly effective

AST of Mycobacterium tuberculosis

MDR and XDR tuberculosis by Mycobacterium tuberculosis infection have occurred

• MDR is resistant to rifampin and isoniazid (the two most effective drugs to treat tuberculosis)

• XDR is resistant not only to rifampin and isoniazid but also to quinolones and other drugs such as aminoglycosides and capreomycin

Drug Susceptibility testing (DST) of Mycobacterium tuberculosis

The drug susceptibility testing (DST) of Mycobacterium tuberculosis is done as:

• Used to determine the resistance of strains isolated before the commencement of treatment

• DST can be demonstrated by:

1. phenotypic susceptibility assay

2. genotypic methods

Phenotypic assays include

1. resistance ration method

2. absolure concentration method

3. proportional method

4. radiometric method

Genotypic methods include

1. DNA sequencing

2. real-time PCR

3. microarrays

4. MTBDR plus assay