The emergence of multi-drug resistant tuberculosis (MDR-TB) defined as combined resistance to the two most effective anti-tuberculosis drugs, rifampicin and isoniazid, threatens to create a public health hazard of unprecedented proportion. The fact that MDR-TR is more difficult and expensive to cure creates the need for prompt diagnosis. Conventionally, the proportion method on Lowenstein Jensen (L J) medium is used in most developing countries as the ‘gold standard’ in the drug susceptibility testing of Mycobacterium tuberculosis (MTB) and it takes 3-4 weeks to give results from an MTB culture. The use of phage as a diagnostic is fast gaining ground today. It involves targeting viable MTB cells from culture with a specific mycobacteriophage. After a one-hour incubation, it is treated with an antivirus to destroy the phages that are not protected with the bacilli. Upon addition of cells of growing, non-pathogenic Mycobacterium smegmatis (sensor cells), progeny phage from the MTB cells infect the sensor cells, thus amplifying the effect of the phage. When plated in an agar medium overnight, plaques occur in the cell lawn indicating the presence of viable MTB in an original sample. A comparison is made between the number of plaques produced in a drug-free control and a sample incubated in the presence of the drug. While the presence of plaques beyond a cut-of point indicates drug resistance, the absence of plaques indicates that the drug destroyed MTB cells. Overall accuracy from several trials so far conducted is put at 97-98% compared with the ‘gold standard’. With the phage amplification method, antituberculosis drug susceptibility results are obtained from MTB culture within 48 hours as opposed to the L J proportion method, which gives resulted in 3 to 4 weeks. Also, phage, as a diagnostic, is much more applicable in Nigeria laboratories than newer, rapid methods which requires specially dedicated instrumentation and are therefore very expensive. Phage amplification technology requires no special equipment and the results can be read visually.
Key words: Tuberculosis, drug susceptibility, phage, treatment, FASTPlaque-TB, rifampicin
(Af J Clinical & Exp Microbiology: 2003 4(2): 67-78)