Antimicrobial susceptibility determined by the E test, Löwenstein-Jensen proportion, and DNA sequencing methods among Mycobacterium tuberculosis isolates discrepancies, preliminary results.
Mycobacterium tuberculosis strains resistant to streptomycin (SM), isoniazid (INH), and/or rifampin (RIF) as determined by the conventional Löwenstein-Jensen proportion method (LJPM) were compared with the E test, a minimum inhibitory concentration susceptibility method. Discrepant isolates were further evaluated by BACTEC and by DNA sequence analyses for mutations in genes most often associated with resistance to these drugs (rpsL, katG, inhA, and rpoB). Preliminary discordant E test results were seen in 75% of isolates resistant to SM and in 11% to INH. Discordance improved for these two drugs (63%) for SM and none for INH when isolates were re-tested but worsened for RIF (30%). Despite good agreement between phenotypic results and sequencing analyses, wild type profiles were detected on resistant strains mainly for SM and INH. It should be aware that susceptible isolates according to molecular methods might contain other mechanisms of resistance. Although reproducibility of the LJPM susceptibility method has been established, variable E test results for some M. tuberculosis isolates poses questions regarding its reproducibility particularly the impact of E test performance which may vary among laboratories despite adherence to recommended protocols. Further studies must be done to enlarge the evaluated samples and looked possible mutations outside of the hot spot sequenced gene among discrepant strains.
Freixo
Maria Inês Moura
MI
Instituto de Microbiologia, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ, Brasil.
Caldas
Paulo C S
PC
Said
Abbadi
A
Martins
Fátima
F
Brito
Rossana Coimbra
RC
Fonseca
Leila de Souza
Lde S
Saad
Maria Helena Féres
MH
D000995:Antitubercular Agents / Q000494:pharmacology*; D001483:Base Sequence; D024881:Drug Resistance, Bacterial; D006801:Humans; D007538:Isoniazid / Q000494:pharmacology; D008826:Microbial Sensitivity Tests / Q000379:methods; D009169:Mycobacterium tuberculosis / Q000187:drug effects*; D012293:Rifampin / Q000494:pharmacology; D013307:Streptomycin / Q000494:pharmacology
D000995:Antitubercular Agents; D007538:Isoniazid; D012293:Rifampin; D013307:Streptomycin