ABSTRACT
Global surveillance has shown that drug resistant [DR] tuberculosis [TB] is widespread. Prompt detection of Mycobacterium tuberculosis drug resistance is essential for effective control of TB. The most frequent mutations associated with Isoniazid [INH] resistance in Mycobacterium are substitutions at codons 315 in the katG gene and the mabA-inhA promoter region [15]. This survey evaluated INH resistant-associated mutations in order to determine rapid detection of TB resistance. Through a descriptive cross-sectional study total of 96 sputum specimens were digested, examined microscopically for acid-fast bacilli and inoculated into L wenstein-Jensen slants. Thereafter, the susceptibility and identification tests were performed on culture positive specimens. Subsequently, the strains were subjected to multiplex allele-specific polymerase chain reaction [MAS-PCR] targeting in the codons 315 in the katG gene and the mabA-inhA promoter region. Distinct PCR banding patterns were observed for different mutation profiles. Drug susceptibility testing revealed that out of 96 available isolates, 30 [31.3%] were susceptible, 36 [37.5%] had multi-drug resistance [MDR-TB] and 30 [31.3%] showed mono-drug resistance. In comparison with the culture-based phenotypic drug susceptibility test, the sensitivity and specificity of MAS-PCR assay for drug resistance-related genetic mutations were 76.7% and 71.4%, respectively. The correlation between MAS-PCR and culture-based phenotypic drug susceptibility testing findings was 99. 4%. The profile of the isolates suggests a significant number of different DR strains with a high frequency of mutations at codon 315 of the katG gene. MAS-PCR provides a rapid, simple and cost-effective method for detecting MDR-TB
ABSTRACT
A link between polymorphisms in the natural resistance -associated macrophage protein gene 1 [Nramp] and susceptibility to tuberculosis [TB] has been demonstrated worldwide. This study aimed to investigate the Nramp1 gene variants among workers exposed to TB bacilli [1-2 hours per day for 1 to 20 years] who did not develop the diseases with those who developed the disease through recent transmission. The polymorphism of Nramp1 at INT4, D543 and 3'UTR was examined in 71 newly smear-positive TB cases and 39 healthcare workers exposed to TB. Polymerase chain reaction [PCR] and restriction fragment length polymorphism [RFLP] were used to genotype Nramp1 polymorphism. Patients' clinical and demographical data were collected. The heterozygote patterns of INT4 [G/C], D543 [G/A] and 3'UTR [+/del] occurred more frequently in control subjects than in patients [P =0.012], respectively [odds: 1.9 CI95%] [1.13-3.12]. Although, the homozygous patterns of INT4 [C/C; 8.5%], D543 [A/A; 1.4%] and 3'UTR [del/del; 1.4%] were only seen in patients [sensitivity 11% and specificity 100%]. The other risk factors like gender, age, resistance and PPD were not associated with Nramp1 gene polymorphism. Individuals with homozygous type mutation have an increased risk of developing tuberculosis. Therefore, we suggest detection of Nramp1 variants in high-risk groups i.e., health workers and close contact cases