title: Correlation between genotypic and phenotypic testing for resistance to rifampin in Mycobacterium tuberculosis clinical isolates in Haiti: investigation of cases with discrepant susceptibility results.
abstract: The World Health Organization has recommended use of molecular-based tests MTBDRplus and GeneXpert MTB/RIF to diagnose multidrug-resistant tuberculosis in developing and high-burden countries. Both tests are based on detection of mutations in the Rifampin (RIF) Resistance-Determining Region of DNA-dependent RNA Polymerase gene (rpoB). Such mutations are found in 95-98% of Mycobacterium tuberculosis strains determined to be RIF-resistant by the "gold standard" culture-based drug susceptibility testing (DST). We report the phenotypic and genotypic characterization of 153 consecutive clinical Mycobacterium tuberculosis strains diagnosed as RIF-resistant by molecular tests in our laboratory in Port-au-Prince, Haiti. 133 isolates (86.9%) were resistant to both RIF and Isoniazid and 4 isolates (2.6%) were RIF mono-resistant in MGIT SIRE liquid culture-based DST. However the remaining 16 isolates (10.5%) tested RIF-sensitive by the assay. Five strains with discordant genotypic and phenotypic susceptibility results had RIF minimal inhibitory concentration (MIC) close to the cut-off value of 1 µg/ml used in phenotypic susceptibility assays and were confirmed as resistant by DST on solid media. Nine strains had sub-critical RIF MICs ranging from 0.063 to 0.5 µg/ml. Finally two strains were pan-susceptible and harbored a silent rpoB mutation. Our data indicate that not only detection of the presence but also identification of the nature of rpoB mutation is needed to accurately diagnose resistance to RIF in Mycobacterium tuberculosis. Observed clinical significance of low-level resistance to RIF supports the re-evaluation of the present critical concentration of the drug used in culture-based DST assays.
authors.affiliation: Center for Global Health, Division of Infectious Diseases, Department of Medicine, Weill Cornell Medical College, New York, New York, United States of America; Les Centres GHESKIO, Port-au-Prince, Haiti.
authors.forename: Oksana
authors.initials: O
authors.lastname: Ocheretina
authors.affiliation: Laboratory of Mycobacteriology, Wadsworth Center, New York State Department of Health, Albany, New York, United States of America.
authors.forename: Vincent E
authors.initials: VE
authors.lastname: Escuyer
authors.affiliation: Les Centres GHESKIO, Port-au-Prince, Haiti.
authors.forename: Marie-Marcelle
authors.initials: MM
authors.lastname: Mabou
authors.affiliation: Les Centres GHESKIO, Port-au-Prince, Haiti.
authors.forename: Gertrude
authors.initials: G
authors.lastname: Royal-Mardi
authors.affiliation: Center for Global Health, Division of Infectious Diseases, Department of Medicine, Weill Cornell Medical College, New York, New York, United States of America.
authors.forename: Sean
authors.initials: S
authors.lastname: Collins
authors.affiliation: Les Centres GHESKIO, Port-au-Prince, Haiti.
authors.forename: Stalz C
authors.initials: SC
authors.lastname: Vilbrun
authors.affiliation: Center for Global Health, Division of Infectious Diseases, Department of Medicine, Weill Cornell Medical College, New York, New York, United States of America; Les Centres GHESKIO, Port-au-Prince, Haiti.
authors.forename: Jean W
authors.initials: JW
authors.lastname: Pape
authors.affiliation: Center for Global Health, Division of Infectious Diseases, Department of Medicine, Weill Cornell Medical College, New York, New York, United States of America.
authors.forename: Daniel W
authors.initials: DW
authors.lastname: Fitzgerald
mesh_terms: D000293:Adolescent; D000328:Adult; D000904:Antibiotics, Antitubercular / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics; D004252:DNA Mutational Analysis; D012321:DNA-Directed RNA Polymerases; D024881:Drug Resistance, Bacterial / Q000235:genetics; D005260:Female; D056726:Genetic Association Studies; D006205:Haiti; D006801:Humans; D007223:Infant; D008297:Male; D008826:Microbial Sensitivity Tests; D008875:Middle Aged; D020125:Mutation, Missense; D009169:Mycobacterium tuberculosis / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification; D020641:Polymorphism, Single Nucleotide; D012293:Rifampin / Q000494:pharmacology*; D014397:Tuberculosis, Pulmonary / Q000188:drug therapy / Q000382:microbiology*; D055815:Young Adult
chemical_list: D000904:Antibiotics, Antitubercular; D001426:Bacterial Proteins; C505805:rpoB protein, Mycobacterium tuberculosis; D012321:DNA-Directed RNA Polymerases; D012293:Rifampin