Mycobactreium Tuberculosis

Mycobacterium tuberculosis complex organisms are obligate pathogens which display >95% DNA / DNA homology: M.tuberculosis, M.bovis, M. bovis bacille Calmette-Guerin (BCG), M.africanum, M.microti, and M.canettii.

Like all microbacteria, members of the M.tuberculosis complex are aerobic, non-spore-forming, non-motile, slightly curved or straight roads.

Phlyctenular keratoconjunctivitis results from a Type IV hypersensitivity (delayed type hypersensitivity) reaction to bacterial antigens like TB, staphylococcal, Chlamydia, and other agents have been implicated.

It is more common among children.

Many patients also have blepharitis.

Patients have multiple lesions, consisting of small yellow-gray nodules (phlyctenules) that appear at the limbus, on the cornea, or on the bulbar conjunctiva and persist from several days to 2 wk.

Of particular importance is the presence of long-chain fatty acids called mycolic acids (for which the mycobacteria are named) and lipoarabinomannan (LAM), a lipid polysaccharide complex extending from the plasma membrane to the surface.

• Delayed-type hypersensitivity (DTH) 
• Cell-mediated immunity (CMI)

M.Tuberculosis is often neutral on gram staining. Once stained it can be decolorised by acid alcohol.

Reference:
Harrisons Principles of Internal Medicine, 18th Edition, Page 134

M. tuberculosis 4–8 weeks is required before growth is detected. New methods have decreased the time required for bacteriologic confirmation of TB to 2–3 weeks.

Reference:
Harrisons Principles of Internal Medicine, 18th Edition, Page 1350

Ans. is ‘b’ i.e., Robert koch

Ans. is b’ i.e., L.J. Medium 

Culture media

.                                     The solid medium most widely employed for routine culture of tubercular is Lowenstein – Jensen Medium (L.J. medium).

Ans. is ‘d’ i.e., Niacin positive

Ans. is ‘a’ i.e. Mycobacterium T.B.

• To fulfill the criteria for fever of unknown origin, a patient must have had

–         an illness of 3 weeks duration

– Fever over 38.3°C on several occasions

– and remain undiagnosed after 1 week of study in the hospital.

• The intervals specified are arbitrary ones intended to exclude patients with protracted but self limited viral illnesses and to allow time for usual radiographic, serologic and cultural studies to be performed.

Etiology

• Common causes – Most cases represent unusual manifestations of common diseases and not rare or exotic diseases e.g. TB., endocarditis, gall bladder disease and H.I.V are more common causes of pyrexia of unknown origin.

Infections associated with Pyrexia of unknown origin

• Both systemic and localized infections can cause pyrexia of unknown origin.
• Tuberculosis and endocarditis are the most common systemic infections but mycoses, viral diseases (particularly infection with Epstein Barr virus and cvtomegalovirus„ toxoplasmosis. Brucellosis. Salmonellosis. Malaria. 0 fever, cat scratch disease) have also been implicated.
• Primary infection with human immunodeficiency virus or opportunistic infections are also associated with Pyrexia of unknown origin.

Neoplasm associated with pyrexia of unknown origin:

• Many cancers can present as fever of unknown origin
• The most common cancers presenting as fever of unknown origin are lymphoma (both Hodgkin’s and non Hodgkin’s) and leukemia.

Ans. is ‘b’ i.e., Inhalation

o Tuberculosis is transmitted mainly by droplet infection and dropled nuclei generated by sputum-positive patients with pulmonary tuberculosis.

o Coughing generates the largest number of droplets of all sizes. The frequency and vigour of cough and the ventilation of the environment influence transmission of infection.

C i.e. Phlycetenular conjunctivitis

Ans. D: LJ medium

Diagnosis of tuberculosis

Microscopy

– Rapid diagnosis

– Low sensitivity. Concentration may increase sensitivity up to hundred folds

– Can not differentiate tuberculosis and non-tuberculosis mycobacteria

– False positive results

– Samples must always be studied with one positive and one negative control

Culture

– The gold standard method for tb diagnosis

Culture in LJ media takes 3 to 6 weeks

– Commonly used rapid culture systems have disadvantages:

1. Radioactive, expensive, blood containing samples give false results
2. All culture methods require decontamination

When grown on LJ medium, M. tuberculosis appears as brown, granular colonies (sometimes called “buff, rough and tough”). The media must be incubated for a significant length of time, usually four weeks, due to the slow doubling time of M. tuberculosis compared with other bacteria (15-20 hours).

Lowenstein-Jensen (g) medium is most widely used for tuberculosis culture.

LJ medium containing glycerol favours the growth of M. tuberculosis while LJ medium without glycerol but containing pyruvate encourages the growth of M. bovis. Both should be used in countries or regions where patients may be infected with either organism.

Ingredients

Mineral salt solution

Potassium dihydrogen phosphate anhydrous (1(1-12PO4) 2.4g Magnesium sulphate (MgSO4. 7H20) 0.24g

Magnesium citrate 0.6g

Asparagine 3.6g

Glycerol (reagent grade) 12m1

Distilled water 600m1

Ans. is ‘a’ i.e., Mycobacterium tuberculosis

Thin painless otorrhoea, multiple perforations of the tympanic membrane and failure to respond to antimicrobial treatment are the features of tubercular otitis media and it is caused by Mycobacterium tuberculosis.

Ans. is ‘b’ i.e., MGIT

• TB bacilli live dormant inside the lung, but do not destroy organs , No signs or symptoms of disease, Not infectious
• Mycobacteria Growth Indicator Tube (MGIT) is intended for the detection and recovery of mycobacteria.
•  The MGIT Mycobacteria Growth Indicator Tube contains 7 mL of modified Middlebrook Broth base. The complete medium, with OADC enrichment and PANTA antibiotic mixture, is one of the most commonly used liquid media for the cultivation of mycobacteria.
• All types of clinical specimens, pulmonary as well as extra-pulmonary (except blood and urine), can be processed for primary isolation in the MGIT tube using conventional methods. 
• After processed specimen is inoculated, MGIT tube must be continuously monitored either manually or by automated instruments until positive or the end of the testing protocol.

Automated Culture methods for M tuberculosis are

1. Radiometric BACTEC ( Bactec Automated Blood Culture System) 46O TB
2. MGIT-960 (Mycobacterial growth indicator tube) OR BACTEC -MGIT 960 system
3. MB/BaCT system
4. ESP II culture system
5. Septic-check AFB method.