Blood agar for susceptibility testing of Mycobacterium tuberculosis against first-line drugs.
OBJECTIVE
To evaluate the performance of blood agar for the susceptibility testing of 50 Mycobacterium tuberculosis clinical isolates against isoniazid (INH), rifampicin (RMP), streptomycin (SM) and ethambutol (EMB).


METHODS
The activity of the drugs was determined by the proportion method on blood agar instead of Middlebrook 7H10 agar according to Clinical Laboratory Standard Institute recommendations. The final concentrations of INH, RMP, SM and EMB were 0.2 microg/ml, 1 microg/ ml, 2 microg/ml and 5 microg/ml, respectively.


RESULTS
The results were compared with the radiometric proportion method as the reference, and the agreements were determined as 100% for INH and RMP, 92% for SM and 96% for EMB. The specificity, sensitivity, positive predictive value and negative predictive value were 90.4% and 97.5%, 100% and 90%, 66.6% and 90% and 100% and 97.5% for SM and EMB, respectively, while these values were 100% for INH and RMP. The results of susceptibility testing were obtained on the 14th day of incubation.


CONCLUSIONS
According to this preliminary study, our results suggest that blood agar can be used as an alternative medium for the susceptibility testing of M. tuberculosis strains against INH, RMP, SM and EMB in resource-limited countries. However, further studies are needed before implementating the method in diagnostic laboratories.
Coban
A Y
AY
Department of Microbiology and Clinical Microbiology, Ondokuz Mayis University Medical School, Samsun, Turkey. noahmet@yahoo.com
Cihan
C C
CC
Bilgin
K
K
Uzun
M
M
Akgunes
A
A
Cetinkaya
E
E
Durupinar
B
B
D000362:Agar; D000995:Antitubercular Agents / Q000494:pharmacology*; D001769:Blood; D003470:Culture Media; D024901:Drug Resistance, Multiple, Bacterial; D004977:Ethambutol / Q000494:pharmacology; D006801:Humans; D066298:In Vitro Techniques; D007538:Isoniazid / Q000494:pharmacology; D008826:Microbial Sensitivity Tests; D009169:Mycobacterium tuberculosis / Q000187:drug effects* / Q000254:growth & development / Q000302:isolation & purification; D012293:Rifampin / Q000494:pharmacology; D018088:Tuberculosis, Multidrug-Resistant / Q000175:diagnosis* / Q000382:microbiology
D000995:Antitubercular Agents; D003470:Culture Media; D004977:Ethambutol; D000362:Agar; D007538:Isoniazid; D012293:Rifampin