I just read a recently published paper titled “Extended-spectrum β-lactamase-producing Enterobacteriaceae in healthy companion animals living in nursing homes and in the community” in American Journal of Infection Control. Unfortunately it is not open access and not easy to find, but it was interesting. Interesting to me mostly from the standpoint of pets being a sentinel of the household. Most of the studies examining ESBL-producing E. coli to date have focused on clinical isolates, so we are ignoring the major reservoir of these bacteria which is the healthy host. Since there appears to be more household sharing of microbes between pet-owner than even between spouses, studying pets is extremely relevant from a human health standpoint. Here, the authors attempted to find ESBL-producing E. coli from dogs and cats coming in for routine vaccinations or at nursing homes using rectal swabs. They looked at a total of 376 samples and found only 9 ESBL-producing isolates, a rate of 2.5%.
I applaud the authors for undertaking this study, as these types of projects are needed to get at the true occurrence of ESBL-producers in healthy animals and humans. I do have some issues with this type of study, though. The prevalence reported here is likely vastly underestimating the true prevalence of ESBL-producers that are out there. When you look at a single isolate from a rectal swab, you are ignoring the entire E. coli population present in an animal and therefore are probably missing a lot of other potential ESBL-producers that are out there. I think what is really needed is a more comprehensive study possibly using pre-enrichment to find ESBL-producers and better characterize the genetic elements encoding for them, the genetic background of the E. coli carrying them, etc. Beyond E. coli, the plasmids carrying many of these ESBL-encoding genes are present in other Proteobacteria that may be in the animal gut but also may be in the environment. What we see in single isolates of E. coli from rectal swabs is likely the tip of the iceberg related to what is actually out there. Using companion animals to measure the occurrence of such traits in bacterial populations is an excellent way to determine what might be floating around in households.