Researchers at the Technical University of Denmark published a paper “Transmission of antimicrobial resistance in the gut microbiome of gregarious cockroaches: the importance of interaction between antibiotic exposed and non-exposed populations” in mSystems that describes a study of antimicrobial resistance (AMR) transmission among cockroaches with implications for AMR transmission in humans.

“…we used a gregarious cockroach, Pycnoscelus surinamensis, as an in vivo animal model for AMR transmission investigations. We explored whether the effect of antimicrobial treatment is detectable with metagenomic sequencing, and whether AMR genes can be spread and established in unchallenged (not treated with antibiotics) individuals following contact with treated donors, and under various frequencies of interaction,” write the investigators.

“Gut and soil substrate microbiomes were investigated by metagenomic sequencing for bacterial community composition and resistome profiling. We found that tetracycline treatment altered the treated gut microbiome by decreasing bacterial diversity and increasing the abundance of tetracycline resistance genes. Untreated cockroaches that interacted with treated donors also had elevated tetracycline resistance.”

cockroach
A scientific team used a gregarious cockroach, Pycnoscelus surinamensis, as an in vivo animal model for antimicrobial resistance transmission investigation. [Chase D’animulls/Getty Images]

The levels of resistance differed depending on the magnitude and frequency of donor transfer. Additionally, treated donors showed signs of microbiome recovery due to their interaction with the untreated ones. Similar patterns were also recorded in the soil substrate microbiomes.

“Our results shed light on how interacting microbiomes facilitate AMR gene transmission to previously unchallenged hosts, a dynamic influenced by the interaction frequencies, using an in vivo model to validate theoretical AMR transmission models.”

Serious threat

AMR represents a serious threat to the health of humans and other animals. With fewer and fewer drugs being effective against some microbial pathogens, infections have become increasingly difficult to treat. Theoretical modeling has been used to explore the spread of AMR through the microbiome of the symbiotic, or nonpathogenic, gut of animals. The present study represents a real-world investigation.

Gregarious insects such as cockroaches permit a simple, easily maintained experimental system to test microbial transmission of AMR. Many cockroach species live in dense groups and have frequent contact, parallel to humans living in urban environments. Researchers added tetracycline to the diet of a population of socially interactive cockroaches. Tetracyclines are a class of antibiotics that treat several kinds of bacterial infections. They observed an increase in abundance of tetracycline resistance genes in their gut microbiomes.

The scientists allowed an untreated population of cockroaches to mix with the tetracycline-treated ones. After interaction with treated cockroaches, the untreated ones also displayed elevated resistance to tetracycline, as did the soil substrate in the habitat which housed the cockroaches. The levels of tetracycline resistance depended on the extent and the frequency of interaction between treated and untreated cockroach populations.

The results of the study illustrate that the direct overuse of antibiotics may not be the only way in which AMR is transmitted; animals carrying AMR genes in their microbiomes can interact with those that do not, facilitating transmission of AMR genes between them. Complementary research in mammals will be needed to confirm these results and extrapolate the findings to humans.

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