Antibiotic-Resistant Bacteria in Returning Travelers

Overview of Antibiotic Resistance

Long before the human era, microbes competed for ecological niches in the environment. Thus, ancient bacteria developed the ability to resist the assault of naturally occurring antibacterial substances, especially those made by fungi and other soil-dwelling organisms. By harnessing these substances (and by developing new antibiotics) for clinical use, we have dramatically accelerated this evolutionary process. The more we expose bacteria to these medications, the sooner we select resistant phenotypes. Nobel Laureate Alexander Fleming warned long ago that this process was inevitable and that medical professionals have an ethical responsibility to use antibiotics in a responsible fashion. Less than a century later, his concerns have proven prophetic. Antibiotic resistance to at least one class of drugs has been documented in almost all bacteria studied, including Gram-positive bacteria (e.g., methicillin-resistant Staphylococcus aureus , vancomycin-resistant Enterococcus , and drug-resistant Streptococcus pneumoniae ), and Gram-negative bacteria (e.g., extended-spectrum beta-lactamase-producing Escherichia coli , MDR Pseudomonas aeruginosa , and carbapenem-resistant Enterobacteriaceae ). Some mechanisms of resistance are specific to a particular species, but in many cases the genetic determinants of resistance lie on mobile elements, such as plasmids and integrons, which can move between species. Thus, in some regions of the world there seem to be ideal conditions for the creation and spread of resistant microbes, in which antibiotic use is uncontrolled and sanitation is insufficient. There is no single, reliable, international surveillance system for detecting and reporting antimicrobial resistance. The World Health Organization oversees a consortium of regional laboratories around the globe, but their funding streams and staffing are often insufficient to generate timely data, especially in sub-Saharan Africa. High-quality data are essential for our understanding of this phenomenon, and they are sorely lacking—this situation needs to change right away. However, the trend is clear: many bacterial infections are becoming tougher to treat worldwide, including in the tropics.

There is no hope of eradicating pathogenic bacteria from the face of the earth with antibiotics—resistance is inevitable. The global question is whether we can reduce, delay, and anticipate the emergence of resistance in a way that helps humans live side-by-side with bacteria in a sustainable way. Our understanding of the human microbiome—the universe of microorganisms on and inside us—is still incomplete. But we do know that more than 90% of the cells on us and in us are microorganisms, so by the numbers we are more “them” than “us.” The notion of human dominance over the microscopic world is naïve, and a more nuanced view of our position in the world is called for. For medical providers dealing with MDRO infections in their individual patients, these questions have very urgent clinical meaning.