Using Roadkill Animals to Study Bacterial Natural Products

In a study recently published in the Journal of Natural Products, researchers from the University of Oklahoma used roadkill to study substances produced by mammalian microbiota (bacteria that normally live within mammals). Their techniques could be used to develop natural therapies derived from bacteria, they say. For example, bacteria isolated from the ear of an opossum produced molecules that inhibited biofilm production by the pathogenic yeast Candida albicans.

Metabolic products of the human microbiota may benefit human health, say the authors. Identifying the genome of the intestinal flora could also make it possible to genetically engineer bacteria to the host’s advantage. “One can envision the potential for generating and applying designer microbes that produce compounds capable of warding off selected pathogens or modulating disease processes,” they write.

The investigators chose to study the microbiota of nonhuman mammals, theorizing that products of these bacteria might have been driven by natural selection and therefore could have a therapeutic benefit. Roadkill, or animals killed by vehicle collision, provided a ready source of bacteria from many species without the need to test live animals.

The researchers collected samples from recently deceased animals along a busy stretch of Oklahoma highway that crosses a state park, agricultural land, and forests. “The juxtaposition of having an active highway that intersects such a variety of mammalian habitats made this a prime location for near daily animal—vehicle collisions,” they write.

The research group collected swab samples from “intact orifices” of animals that had been dead for a short time, usually less than 10 hours. Animals sampled (in descending order of frequency) were opossums, squirrels, raccoons, deer, armadillos, and skunks. Bacteria isolated from the swabs underwent laser ablation electrospray ionization mass spectrometry and bioassays to identify their metabolic products. The investigators also analyzed the bacterial genomes.

Of the 3659 bacterial species isolated from the animal carcasses, 39% were from opossums. The most common bacteria found were Gammaproteobacteria (mouth, nose, ear, and upper gastrointestinal tract) and Fusobacteria (rectum).

In a screening bioassay, a Pseudomonas species and a Serratia species isolated from the ear of an opossum inhibited C. albicans biofilm formation but did not kill the yeast cells. Further analysis showed that the Pseudomonas species produced the metabolite viscosin, and the Serratia species produced serrawettin. Viscosin and serrawettin are cyclic lipodepsipeptides (types of biosurfactants), and inhibiting biofilm production affects yeast’s ability to adhere to surfaces. “The abilities of these bacterial cyclic lipodepsipeptides to limit biofilm formation, while not impacting yeast cell survival, hint at the possibility of alternative chemical options for controlling C. albicans infections by means of biofilm modulation,” write the authors.

Because the composition of the normal bacterial flora changes after death, the use of roadkill could limit the applicability of this study, say the investigators. However, they write, sampling undamaged orifices of freshly killed animals reduced the effects of environmental contamination and decomposition, so their isolates most likely were true representatives of the mammalian microbiota.

Sampling roadkill is a humane way to obtain bacteria from many species, say the authors, noting that nonhuman mammalian microbiota may provide a source of new natural products. “The discovery pipeline presented here is an enabling tool for identifying bacterial natural products from nonhominid mammals,” they conclude.

Dr. Laurie Anne Walden received her doctorate in veterinary medicine from North Carolina State University. After an internship in small animal medicine and surgery at Auburn University, she returned to North Carolina, where she has been in small animal primary care practice for over 20 years. Dr. Walden is also a board-certified editor in the life sciences and owner of Walden Medical Writing, LLC. She works as a full-time freelance medical writer and editor and continues to see patients a few days each month.