Characteristics of Arthrobacter cumminsii, the Most Frequently Encountered Arthrobacter Species in Human Clinical Specimens

During a 2-year period, 10 strains of Arthrobacter cumminsii were isolated in or received by a Swiss routine clinical bacteriology laboratory, and 5 further isolates were referred to a Swedish bacteriology reference center over a 5-year period, making A. cumminsii the most frequently encountered Arthrobacter species in these two laboratories. The present report outlines the clinical features of the 15 A. cumminsii strains and presents an extended biochemical characterization of this microorganism. A. cumminsii exhibits a unique cellular fatty acid pattern with the consistent presence of C(14:0i) and C(14:0) fatty acids as well as relatively large amounts of C(16:0i) and C(16:0) fatty acids usually not seen in other Arthrobacter spp. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis was found to be a useful tool for confirmation of the identification of A. cumminsii. The MICs of 39 antimicrobial agents were determined, and it was demonstrated that aminoglycosides and quinolones had only weak activities against A. cumminsii strains, in contrast to their activities against most other coryneform bacteria. As a result of the extended characterization of A. cumminsii, an emended description of this species is presented. Due to the lack of A. cumminsii in established identification systems, it is most likely that this species is underdiagnosed in many routine clinical bacteriology laboratories.