Evolution of honey resistance in experimental populations of bacteria depends on the type of honey, and has no major side effects for antibiotic susceptibility

With rising antibiotic resistance, alternative treatments for communicable
diseases are increasingly relevant. One possible alternative for some
types of infections is honey, used in wound care since before 2000 BCE and
more recently in licensed, medical-grade products. However, it is unclear
whether medical application of honey results in the evolution of bacterial
honey resistance, and whether this has collateral effects on other
bacterial traits such as antibiotic resistance. Here, we used single-step
screening assays and serial transfer at increasing concentrations to
isolate honey-resistant mutants of Escherichia coli. We only
detected bacteria with consistently increased resistance to the honey they
evolved in with two of the four tested honey products, and the observed
increases were small (maximum two-fold increase in IC90). Genomic
sequencing and experiments with single-gene knockouts showed a key
mechanism by which bacteria increased their honey resistance was by
mutating genes involved in detoxifying methylglyoxal, which contributes to
the antibacterial activity of Leptospermum honeys.
Crucially, we found no evidence that honey adaptation conferred
cross-resistance or collateral sensitivity against nine antibiotics from
six different classes. These results reveal constraints on bacterial
adaptation to different types of honey, improving our ability to predict
downstream consequences of wider honey application in medicine.