Môi trường lowenstein jensen

Introduction

Tuberculosis has been for many centuries the most important of the human infections, in its global prevalence, its devastating morbidity and its massive mortality. Despite many advances in its diagnosis and treatment, the problem of tuberculosis is on its rise, both globally and in India. At present, the global incidence of this disease is increasing at the rate of 0.4 % per year [1].

It has been estimated that a third of the world’s population, about 2 billion people, are infected with the tubercle bacilli. Every year, between 8 and 9 million new cases of tuberculosis appear and 3 million persons die from the disease [2].

A large majority of the cases and deaths are reported from the poor nations. India is one of the worst affected countries. More than 40 % of the population is infected and some 15 million suffer from tuberculosis in our country, of which over three million are highly infectious open cases. In 2009, out of the estimated global incidence of 9.4 million TB cases, 2 million were estimated to occur in India [3].

With the progress of the AIDS pandemic, tuberculosis has become a problem for the rich nations also. A close relationship has emerged between tuberculosis and HIV.

The worldwide spread of Multi Drug Resistant Tuberculosis (MDRTB) has added new troubles to the already existing problem. At present, 3.2 % of the world’s new cases of TB are multi drug resistant [4]. In India, the incidence of MDRTB ranges from 1.3 to 3% [5].

The most effective control measure for checking the spread of TB is to detect it early and to treat it optimally at the earliest. Although ZN staining smear microscopy is most commonly employed for an early detection, it is rather insensitive and it fails to detect a large number of cases [6].

Under these circumstances, the cultivation of Mycobacterium tuberculosis provides a sensitive and a specific means for the diagnosis of TB. The conventional culture methods such as the use of Lowenstein Jensen medium requires 3 to 6 weeks for its isolation, plus an additional 1 to 2 weeks for its speciation. Such a prolonged turnaround time in the diagnosis is unacceptable, as rapid detection and identification of MTB is essential both for medical and epidemiological purposes [7].

Thus, there is a need of a culture method that is reliable and which has a short turnaround time. Each method has its own advantages and disadvantages, starting from the LJ medium and the Middlebrook 7H 10 medium (MB7H10) to the present trendy and speedy automated methods like the MB/BACT 3D device [8-13]. MB/BACT is a safer and a quicker method as it is an automated method which involves liquid media and as it does not involve any radioactive material.

The MB/BACT Mycobacteria Detection System utilizes a colourimetric sensor and reflected light to monitor the presence and the production of carbon dioxide (CO2) which is dissolved in the culture medium. If microorganisms are present in the test sample, carbon dioxide is produced, as the organisms metabolize the substrates present in the culture medium. When the growth of the microorganisms produces CO2, the colour of the gas permeable sensor which is installed in the bottom of each culture bottle, changes from blue-green to yellow. The lighter colour results in an increase in the reflectance units, as is monitored by the system. The bottle reflectance is monitored and recorded by the instrument every 10 minutes. MB BACT requires one person who is good at computer basics and is trained, in order to feed the data of the sample and to take the bar code reading. Even though the cost of each MB/BACT bottle is costlier as compared to the conventional LJ medium and the MB7H10 agar, it is cost effective in identifying the growth 1-2 weeks earlier and with even minimum amount of growth.

In the present study, an attempt was made to access the feasibility of using the MB7H10 medium and the MB/BACT 3D device as primary isolation media for MTB. They have been compared with the LJ medium, which is the gold standard.