Dual spectinomycin-streptomycin resistance marker in Brucella spp.

Pathogenic microbiology investigators have a responsibility to consider the public health implications of their research, including the experimental introduction of antibiotic resistance markers that could influence the treatment of infectious diseases. Furthermore, the reviewers for Infection and Immunity as well as other scientific journals are asked to evaluate submitted manuscripts for the occurrence of “misuses of microbiology or of information derived from microbiology”(1). But the importance of resistance to multiple antibiotics conferred by single marker genes is not always recognized. A case in point is the bacterial aadA1 gene in the omega fragment, originally from plasmid R100.1 (6). The use of this marker has recently been reported for gene disruption in Brucella suis with selection for resistance against spectinomycin, an antibiotic not used in the treatment of brucellosis (5). However, this marker also confers resistance to streptomycin, a frontline antibiotic frequently included in therapeutic protocols for brucellosis (2). This point may be particularly important for this organism due to its status as a relatively frequent cause of laboratory-acquired infection and its classification as a risk group 3 pathogen, a CDC select agent, and a USDA high-consequence livestock pathogen (3, 4, 7). There may be implications for other investigators considering the use of the same marker or interested in obtaining the recombinant streptomycin-resistant Brucella strains reported in reference 5. Alternative markers not conferring resistance to streptomycin should be used or developed to avoid these problems associated with aadA1 in Brucella spp.