Molecular epidemiology of fluoroquinolones-resistant mycobacterium tuberculosis by MIRU-VNTR gentoyping

Abstract

Abstract of thesis entitled “Molecular Epidemiology of Fluoroquinolones-resistant Mycobacterium tuberculosis by MIRU-VNTR Genotyping” Submitted by Yuen Suk Han for the degree of Master of Philosophy at The University of Hong Kong in October 2019

Multidrug-resistant tuberculosis (MDR-TB) is an essential global public health concern. Fluoroquinolones and second-line injectable drugs are used in MDR-TB treatment. In general, the laboratory results for diagnosis of tuberculosis (TB) and phenotypic drug susceptibility testing are available in few months. Besides, gyrase mutation in Mycobacterium tuberculosis (MTB) could not account for all fluoroquinolones resistance. Other fluoroquinolones-resistant (FLQs-R) mechanisms in MTB genome such as efflux pump and MfpA PRP expression, which has been associated with the elevation of fluoroquinolones minimum inhibition concentration and reported in Mycobacterium strains other than MTB. Moreover, the epidemiology of FLQs-R MTB in Hong Kong remains unknown.

This study aims at the correlation of FLQs-R isolates with their genotypic mutations and the molecular epidemiology of FLQs-R isolates was investigated using Mycobacterial Interspersed Repetitive Units-Variable Number Tandem Repeat (MIRU-VNTR) typing.

A total of 73 MTB isolates were tested by DNA Sanger sequencing for the quinolone resistance determining region (QRDR) of the gyrA gene. Among these 73 MTB isolates, 22 FLQs-R isolates with most common mutations were detected in codon 90 (5 out of 22, 22.7%) and codon 94 (15 out of 22, 68%) of QRDR gyrA gene. Novel mutation among FLQs-R MTB was not detected and MDR-TB strains were highly associated with FLQs-resistance (18/22, 81%).

Among 73 clinical isolates of MTB, 71 from 61 non-duplicating TB cases were studied by the 24-loci MIRU-VNTR typing. Analysis revealed 61 isolates were linked with West African lineage I (2 out of 31, 3.3%), Euro-American lineage (3 out of 31, 4.9%), Indo-Oceanic lineage (6 out of 61, 9.8%), and East Asian lineage (48 out of 61, 78.7%) respectively. The predominant East-Asian lineage was associated with pulmonary TB infection and 20 (20 out of 21, 95%) were FLQs-R strains. Among these FLQs-R strains, there were 4 clusters without epidemiological linkage. From each cluster, predominant FLQs-R MTB variant was identified with no statistically significant difference (p>0.05) during time of infection.

In conclusion, understanding the epidemiology of FLQs-R MTB stains can assist to minimize the gap in TB detection and treatment. Early detection facilitates not only patient treatment, but also minimize TB spread from transmission. The phenotypic susceptibility test for fluoroquinolones in MTB can be predicted by genotypic testing, which shortens the time of detection for fluoroquinolones resistance. Most of MDR-TB isolates in this study also acquired fluoroquinolones resistance, the use of fluoroquinolones in MDR-TB treatment should be cautioned. (word count: 396 words)