comparative of phenotypic tests in aerobic actinomycetes

dear editor,i read with interest article that published entitled *isolation and identification of bioactive compound producing rhodococcus spp. isolated from soil samples {ijmcm/5(1) (2015) 463-468}* [1]. some of the genus such as nocardia, gordonia, mycobacterium and rhodococcus are in actinomycete family and they are gram-positive and partially acid-fast. rhodococcus species usually stain gram-positive. cells form as cocci or short rods which grow in length, and may form an extensively branched vegetative mycelium which may fragment. microscopic aerial hyphae and spores are not usually produced. they are also non-motile. they are usually partially acid-fast due to the mycolic acid in their cell walls. colonies of other rhodococci may be rough, smooth or mucoid and pigmented cream, buff, yellow, coral, orange or red. although biochemical tests help to distinguish rhodococcus from other organisms, differentiation from other aerobic actinomycetes can be difficult. colonial and cell morphology cannot be used to distinguish among rhodococcus, gordonia and tsukamurella species. i listed some of phenotypic characterization of nocardia, gordonia, mycobacterium, rhodococcus and corynebacterioum in table 1 [2-9] and showed phenotypic tests such as microscopic examination, gram and acid-fast staining, catalase, oxidase and motility tests that used by aghaei et al is insufficient for the genus rhodococcus confirmation. in literature, results of phenotypic tests are ambiguous for rhodococcus identification and cannot distinguish the genus gordonia of rhodococcus [10]. authors do not explain about phenotypic tests results in this article and results are equivocal.