Commensals: Underappreciated Reservoir of Antibiotic Resistance

A ntibiotic resistance, reported for sulfonamides in the mid-1930s and for penicillins in the 1940s, remains a stubborn quandary. What was once confined mainly to hospitals increasingly involves multidrug resistance that encompasses communities and encircles the globe. Virtually all types of bacterial infections are becoming resistant to antibiotic treatments, according to officials at the Centers for Disease Control and Prevention in Atlanta, Ga. Yet, despite decades of grappling with these issues, we still do not understand fully how genes carrying resistance traits spread, what makes certain species highly promiscuous in transferring those traits, whether there are effective barriers to their spread, and the frequency with which resistance genes move independently or in tandem with other migrating genes. While evidence points to microorganisms associated with food, animals, and water as the main sources for resistance genes, which of them exerts the most impact is not known. We also do not know how important a role the burgeoning aquaculture industry plays, particularly in those countries where such farms are poorly regulated and may not only abuse antibiotics but sometimes even operate within the confines of wastewater treatment plants. Equally worrisome are the sludge products of urban and rural wastewater treatment plants that are increasingly used for fertilizer—dispersing unknown amounts of resistance genes and antibiotics that withstand standard sewage treatment. In 2008, the Alliance for the Prudent Use of Antibiotics (APUA) convened microbiologists and other experts to review these and related questions and also to address the role of commensal and other nonpathogenic microorganisms in the overall problem of antibiotic resistance development and disSummary