Williamsia spp. are emerging opportunistic bacteria

Actinomycetes that have mycolic acid in the cell walls have been classified under genera such as Corynebacterium, Gordonia, Mycobacterium, Nocardia, Rhodococcus, Tsukamurella, Skermania and Williamsia [1]. Williamsia was introduced in 1999 by Kämpfer et al. [2] to accommodate actinomycetes with atypical cell morphology and mycolic acids with 50 to 56 carbon chain lengths between the genera of Rhodococcus and Gordonia. Members of the genus Williamsia are Gram-positive, aerobic, rod and coccoid shaped, smooth and orange-red pigmented (in some species) colonies and not acid-fast bacteria, and consist of straight-chain saturated, unsaturated and 10-methyl-branched components that currently comprise 11 recognized species which have been isolated from human clinical specimens and environmental resources [3,4]. According to reports, Williamsia deligens, W. muralis and W. serinedens have been isolated from immunocompromised patients with diabetes mellitus, as well as elderly patients. The most commonly reported sources of Williamsia infection include pulmonary infection [5], bacteraemia [4], endophthalmitis [3] and perinatal sepsis [6]. In addition, evidence indicates that Williamsia serinedens is able to grow in oilcontaminated soil; this bacterium is likely to be effective in the biodegradation process and in the decomposition of industrial pollution from soil [7]. Members of aerobic actinomycetes are increasing by discovering new species, and clinical microbiologists will face problems identifying them. Phenotypic tests are unable to identify actinomycetes and differentiate