Lipiarmycin targets RNA polymerase and has good activity against multidrug-resistant strains of Mycobacterium tuberculosis.
OBJECTIVE
The aim of this study was to determine the in vitro activity of lipiarmycin against drug-resistant strains of Mycobacterium tuberculosis (MTB) and to establish the resistance mechanism of MTB against lipiarmycin using genetic approaches.


METHODS
MIC values were measured against a panel of drug-resistant strains of MTB using the broth microdilution method. Spontaneous lipiarmycin-resistant mutants of MTB were tested for cross-resistance to standard anti-TB drugs, and their rpoB and rpoC genes were sequenced to identify mutations.


RESULTS
Lipiarmycin exhibited excellent inhibitory activity against multidrug-resistant strains of MTB with MIC values of <0.1 mg/L. Sequence analysis of the rpoB and rpoC genes from spontaneous lipiarmycin-resistant mutants of MTB revealed that missense mutations in these genes caused resistance to lipiarmycin. Although both lipiarmycin and rifampicin are known to inhibit the bacterial RNA polymerase, the sites of mutation in the rpoB gene were found to be different in MTB strains resistant to these inhibitors. Whereas all six rifampicin-resistant MTB strains tested had mutation in the 81 bp hotspot region of the rpoB gene spanning codons 507-533, 16 of 18 lipiarmycin-resistant strains exhibited mutation between codons 977 and 1150. The remaining two lipiarmycin-resistant strains had mutation in the rpoC gene.


CONCLUSIONS
Lipiarmycin has excellent bactericidal activity against MTB and lacks cross-resistance to standard anti-TB drugs. Furthermore, rifampicin-resistant strains remained fully susceptible to lipiarmycin, and none of the lipiarmycin-resistant MTB strains became resistant to rifampicin, highlighting the lack of cross-resistance.
Kurabachew
Mekonnen
M
Novartis Institute for Tropical Diseases, 10 Biopolis Road, #05-01 Chromos, Singapore 138670.
Lu
Stephen H J
SH
Krastel
Philipp
P
Schmitt
Esther K
EK
Suresh
Bangalore L
BL
Goh
Anne
A
Knox
John E
JE
Ma
Ngai Ling
NL
Jiricek
Jan
J
Beer
David
D
Cynamon
Michael
M
Petersen
Frank
F
Dartois
Veronique
V
Keller
Thomas
T
Dick
Thomas
T
Sambandamurthy
Vasan K
VK
D000220:Adaptation, Biological; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution / Q000235:genetics; D000617:Aminoglycosides / Q000494:pharmacology*; D000995:Antitubercular Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics; D004252:DNA Mutational Analysis; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D012321:DNA-Directed RNA Polymerases / Q000037:antagonists & inhibitors*; D000077732:Fidaxomicin; D006801:Humans; D008826:Microbial Sensitivity Tests; D050296:Microbial Viability; D008958:Models, Molecular; D008969:Molecular Sequence Data; D020125:Mutation, Missense; D009169:Mycobacterium tuberculosis / Q000187:drug effects* / Q000302:isolation & purification; D012293:Rifampin / Q000494:pharmacology; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D018088:Tuberculosis, Multidrug-Resistant / Q000382:microbiology*
D000617:Aminoglycosides; D000995:Antitubercular Agents; D001426:Bacterial Proteins; D004269:DNA, Bacterial; C505805:rpoB protein, Mycobacterium tuberculosis; D012321:DNA-Directed RNA Polymerases; D012293:Rifampin; D000077732:Fidaxomicin