Gerard Wright and colleagues have documented the presence of antibiotic resistance in the microbiome of a cave that has been isolated for more than 4 million years and used elegant methods to show that the mechanisms of resistance include enzymes circulating in modern drug-resistant pathogens [1]. This work confirms and extends Wright’s previous remarkable study of a collection of antibiotic resistance genes from 30,000 year-old permafrost sediments [2].

I thank the authors for finding and referencing our 1970 article reporting the detection of transferable antibiotic resistance plasmids in the fecal flora of an antibiotic virgin population living in a remote area of Borneo [3]. Like the current authors, we concluded that antibiotic resistance was a natural phenomenon that predated human use of antibiotics. I differ, however, with the authors’ interpretation of our data. They reference our article as evidence that plasmids from bacterial collections that predate the antibiotic era are largely devoid of resistance elements. While it is true that we detected resistance plasmids from only 6 strains of Escherichia coli isolated from 128 individuals, our observation clearly documents their presence in a pre-antibiotic community of human beings.

The presence of antibiotic resistance genes in pre-antibiotic communities suggests that their presence provides ecological advantages to bacteria independently of anthropogenic use of antibiotics. The presence of resistance genes in ancient bacteria, however, should only serve as a further caution against the indiscriminate use of antimicrobial compounds. The genetic elements have been present for millions of years and just waiting for further selective pressure.

1. Bhullar K, Waglechner N, Pawloski A, Koteva K, Banks ED, et al. (2012) Antibiotic Resistance is Prevalent in an Isolated Cave Microbiome. PLoS ONE 7(4): e34953. doi:10.1371/journal.pone.0034953.

2. D’Costa VM, King CE, Kalan L, Morar M, Wilson WLSung, et al.(2011) Antibiotic Resistance Is Ancient. Nature 477 (7365): 457-61. doi: 10.1038/nature10388.

3. Davis CE, Anandan J (1970) The evolution of r factor. A study of a “preantibiotic” community in Borneo. N Engl J Med 282: 117-122.