A review in Applied and Environmental Microbiology from earlier this year provided evidence for an elusive link in antibiotic resistance. Livestock that are used for food are fed antibiotics to increase their body mass. This creates a selective pressure for antibiotic resistance in their gut, and it is well known that many antibiotic resistant strains originate in these animals. There is now mounting evidence that the antibiotic resistant strains of bacteria seen in humans are actually those same strains that originated from livestock. How, though, is this antibiotic resistance being transferred from animals to humans? According to this review: insects!
The authors detail studies showing that the feces of livestock animals contain many antibiotic resistant bacteria. Other studies have shown that many insects found in farms can acquire these antibiotic resistant strains in their own guts by feeding off the feces of the animals. The connection to humans is demonstrated in studies showing that when insects land on human food to eat, they can transfer their gut microbiome to these surfaces. Thus the vector of antibiotic resistance between animals and humans is the guts of insects. Furthermore, the authors show the same horizontal gene transfer that spreads antibiotic resistance in the guts of animals and humans also occurs in insects.
The authors of this article conclude that there should be an increase in pest control in farms, restaurants, and kitchens. Antibiotic resistance is a growing problem, and small measures like keeping flies away from our food are certainly worthwhile. Still, the most obvious solution is to outlaw antibiotic use in livestock all together, something that Europe has done since 2006.