Prevalence of isoniazid resistance-conferring mutations associated with multidrug-resistant tuberculosis in Free State Province, South Africa.

BACKGROUND: Multidrug- and extensively drug-resistant tuberculosis (MDR-TB and XDR- TB) threaten local and global control of the disease. The molecular line-probe assay (LPA) provides rapid diagnosis and early management of MDR-TB. The LPA detects mutations of katG and inhA genes associated with isoniazid (INH) resistance in Mycobacterium tuberculosis isolates. The katG and inhA genes are associated with high- and low-level INH resistance, respectively, as well as cross-resistance to ethionamide in the case of inhA gene mutations. Patients with MDR-TB due to an inhA mutation could benefit from the use of high-dose INH - instead of ethionamide - in their MDR-TB regimen. OBJECTIVES: To determine the frequencies of katG and inhA mutations that conferred INH resistance among MDR-TB isolates during 2014 - 2016 in Free State (FS) Province of South Africa. METHODS: We retrospectively reviewed MDR-TB isolates assayed with GenoType MTBDRplus (Hain Lifescience, Germany) (LPA) at the central TB laboratory of Universitas Academic Hospital, Bloemfontein, FS, and calculated the frequencies of katG and inhA mutations. RESULTS: Among 918 MDR-TB isolates, the prevalence of katG, inhA and katG plus inhA mutations was 63.9%, 13.4% and 22.7%, respectively. Approximately 60% (n=536; 58.4%) of the isolates were obtained from male patients. The patients' ages ranged from 1 to 89 (median 37) years. The Xhariep district had the highest incidence of INH resistance-conferring mutations in the province. CONCLUSIONS: katG-associated mutations are the predominant INH resistance-conferring mechanism among MDR-TB isolates in the FS. Patients infected with isolates that harbour the katG mutation are unlikely to benefit from high-dose INH therapy in the bedaquiline (BDQ)-containing modified short MDR-TB regimen. They may, however, benefit from the inclusion of ethionamide in the regimen. Dual katG and inhA gene mutations make these patients unlikely to respond to either high-dose INH or ethionamide and should now be considered for either the BDQ-containing long MDR-TB regimen or an individualised treatment regimen, depending on fluoroquinolone susceptibility. Clinicians should familiarise themselves with interpreting various INH resistance-conferring mutation results and their implications for management of MDR-TB treatment.

The diagnosis of skeletal tuberculosis by polymerase chain reaction.

OBJECTIVE: To determine the potential of the polymerase chain reaction (PCR) for detecting Mycobacterium tuberculosis in skeletal samples by comparing results obtained by 1) Ziehl Neelsen staining, Lowenstein-Jensen and Bactec culture, 2) histopathology and clinical findings at the level of agreement, sensitivity and specificity. DESIGN: Cross sectional study. SETTING: Department of Medical Microbiology, Orthopaedics and Anatomical pathology, University of the Orange Free State Bloemfontein, South Africa. SUBJECTS: 45 consecutive patients were extensively investigated, 30 patients with clinical presumptive active tuberculosis and 15 with other pathology. RESULTS: Detection using culture could confirm only three of the 26 clinically diagnosed tuberculosis cases while PCR detection confirmed disease in 15 cases. The use of PCR increased the confirmation of clinically probable tuberculosis from 14 using standard laboratory techniques and histology to 18 of 26 cases. Calculated sensitivity and specificity for PCR employing culture as the "gold standard" were 100% (with 95% CI 29.2; 100.0) and 71.4% (55.4; 84.3), which due to low detection levels, basically excludes culture as a standard for statistical analysis. Sensitivity and specificity for PCR using histology as the "gold standard" were 78.6% (49.2; 95.3) and 87.1% (70.2; 96.4) respectively with positive and negative predictive values of 73.3% (44.9; 92.2) and 90% (73.5; 97.9) respectively. Positive agreement between PCR and histology was 0.64 (0.4; 0.9) indicating fair agreement. CONCLUSION: Although numbers in the study were too low to effectively draw statistically valid conclusions the importance of the relevance of PCR for rapid detection of low numbers of acid-fast bacilli and confirmation of mycobacterial infection in spinal biopsies has been established.