Application of the antibiotic batumin for accurate and rapid identification of staphylococcal small colony variants

Background Staphylococcus aureus is a major human pathogen causing significant morbidity and mortality. The S. aureus colonies in osteomyelitis, in patients with cystic fibrosis and patients with endoprosthesis rejection frequently have an atypical morphology, i.e. staphylococcal small-colony variants, which form a naturally occurring subpopulation of clinically important staphylococci. Identification of these small colony variants is difficult, because of the loss of typical phenotypic characteristics of these variants. We wanted to improve and simplify the diagnosis of staphylococcal infection using a diagnostic preparation, consisting of 5 μg batumin paper disks. Batumin possesses a unique selective activity against all studied Staphylococcus spp., whereas all other species tested thus far are batumin resistant. We assessed the efficacy of the batumin diagnostic preparation to identify staphylococcal small colony variants, isolated from osteomyelitis patients. Findings With the batumin diagnostic preparation, all 30 tested staphylococcal small-colony variants had a growth inhibition zone around the disk of minimum 25 mm, accordant with the inhibition zones of the parent strains, isolated from the same patients. Conclusions The batumin diagnostic preparation correctly identified the small-colony variants of S. aureus, S. haemolyticus and S. epidermidis as belonging to the genus Staphylococcus, which differ profoundly from parental strains and are difficult to identify with standard methods. Identification of staphylococcal small-colony variants with the batumin diagnostic preparation is technically simple and can facilitate practical laboratory work.