Microbiological Pathology, Sefako Makgatho Health Science University, Pretoria, South Africa 2

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1 The Incidence of discordant Rifampicin susceptibility results between genotypic and phenotypic methods in Mycobacterium tuberculosis complex isolates at Dr George Mukhari Hospital Tertiary Laboratory, NHLS Maluleka C 1;2, Shikwambane-Ntlemo G 1, 2, NA Makhado 1, 2,, and M. Nchabeleng 1,2 1 Microbiological Pathology, Sefako Makgatho Health Science University, Pretoria, South Africa 2 National Health Laboratory Services (NHLS) Dr George Mukhari tertiary Laboratory, Pretoria, South Africa

2 OVERVIEW Introduction Methods Results Discussion Conclusion

3 INTRODUCTION Tuberculosis (TB) is one of the world s most important infectious causes of morbidity and mortality (Steingart et al., 2013) The prevalence of drug-resistant (MDR & X-DR)-TB is also rising globally, posing a serious threat to TB control WHO has endorsed phenotypic and genotypic assays for rapid detection of MDR-TB Frequent discordant results between phenotypic and genotypic DST methods

4 AIM OF THE STUDY To determine the incidence of discordant RIF susceptibility results between the genotypic and phenotypic DST assays

5 METHODS Line Probe Assay - MTBDRplus MGIT 960 culture and DST RIF r RIF s 100 Clinical Isolates Sequencing of rpob Medical records for clinical outcome

6 RESULTS Distribution of sequencing results Total: 100 Interpretable:71 Mutations: 69 Agreement between methods: LPA & Sequencing: 97.2% MGIT 960 & Sequencing : 2.8%

7 RESULTS CONT.. Table 1: Characteristics of participants (n=69) Parameter Total (n) (%) Age HIV status HIV positive HIV negative Total

8 RESULTS CONT.. Table 1. Distribution of mutations Mutated codon Specific mutation/s Mutated isolates n (%) Amino acid DNA codon/s 531 Ser Leu TCG TTG 26 (37.6) 526 His Leu CAC CTC 9 (13 ) 526 His Asp CAC GAC 10 (14.4) 526 His Try CAC TAC 6 (8.6) 526 His Asn CAC AAC 2 (2.8) 516 Asp Val GAC GTC 2 (2.9) 511 Leu Pro CTG CCG 6 (8.7) 218 Asn His AAC CAC 2 (2.8) 586 phe Val TTC GTG 1 (1.4) 585 Ser Arg TCG CGA 1 (1.4) 574 Ser Arg TCC AGG 1(1.4) 390 Val Gly GTT GGA 1 (1.4) 533 Leu Pro TTA CCT 2 (2.8) Total 69

9 RESULTS CONT.. Table 3: Correlation between mutations and clinical outcome Clinical outcome Number Mutations Cured 2 Val390Gly Hist 526 Leu Completed 17 Hist526Leu (8) Leu511Pro(5) Asp 516Val (1) Leu533Pro(1) Ser574Arg(1) Defaulted 3 Phe586Val (1) Hist 526 Leu(2) Died 5 Ser531Leu(4) Leu511Pro (1) In Sizwe hospital 1 Ser531Leu Lost to follow-up 38

10 DISCUSSION A total of 100 samples were sequenced and 71 (71%) yielded interpretable results Sequence analysis revealed 69 (97%) samples with rpob mutations that were in agreement with genotypic LPA Two (3%) isolates yielded no rpob mutation with sequencing, in agreement with phenotypic DST (MGIT 960) Most of these patients (77.5%) were co-infected with HIV

11 DISCUSSION CONT.. The most prevalent mutation was Ser531Leu found in 26 (38%) of samples which was in agreement with other studies done in South Africa Mutations outside the rpob gene were also noted e.g N218 and V390G in 1(1.4)

12 DISCUSSION CONT. Two patients- cured, 17 completed treatment but clinically still not improving Five patients died while on treatment (MUT 531 4pts) Thirty eight patients were lost to follow up

13 CONCLUSION The 531 rpob mutation is associated with poor clinical outcome This study shows that DNA sequencing is the best suited for evaluating suspected drug-resistant Mycobacterium tuberculosis isolates with discordant phenotypic/molecular susceptibility results This study also suggests an association of poor outcomes among patients with rpob mutations not conferring phenotypic resistance Additional studies of these rpob mutations are needed to confirm their role in treatment outcome

14 REFERENCES. 1. Sewpersadh M, Erasmus L, Bapela N, Van der walt M, Phenotypic and genotypic Discordant Drug resistance Mycobacterium tuberculosis isolates identified from South Africa (2012). Am J Respir Crit Care Med. 2012; Van Deun A., Barrera L., Bastian I., Fattorini L., Hoffmann H., Kam K.M, Rigouts L., Rusch-Gerdes S. and Wright A. Mycobacterium tuberculosis strains with highly discordant Rifampicin susceptibility test results. J Clin Microbiol 2009; 47 (11): World Health Organization Treatment of tuberculosis: guidelines for national programmes, 4 th Ed. World Health Organization document WHO/HTM/TB/ WHO, Geneva, Switzerland

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