Long-term macrolide therapy has been shown to provide benefit to those with a range of chronic respiratory conditions. However, there remain concerns about the impact of macrolide exposure on the carriage and abundance of antibiotic resistance genes within the oropharynx. The potential for onward transmission of resistance from macrolide recipients to their close contacts is also poorly understood.
Does long-term macrolide use impact carriage of resistance within the oropharyngeal microbiota in people with chronic respiratory conditions and risk of onward transmission to their close contacts?
Oropharyngeal swabs were collected from 93 individuals with chronic respiratory conditions, of whom 53 were receiving long-term macrolide therapy. An oropharyngeal swab was also collected from a close co-habiting contact of each subject. Detection and abundance of ten macrolide-associated resistance genes with the potential to disseminate via horizontal gene transfer were assessed by quantitative PCR.
Detection of resistance genes in macrolide recipients was comparable to that in non-recipients. However, the normalised gene abundance of erm(B) was significantly higher in the macrolide recipient group (p=0.045). In the close contacts, no between-group differences in resistance gene detection or abundance were identified. Within-group analysis showed that the detection of erm(F) and mef in macrolide recipients, but not non-recipients, was significantly associated with detection in close contacts (p=0.003 and p=0.004 respectively). However, between-group analysis showed that treatment group did not predict co-carriage between patients and their close contacts (p>0.05 for each gene).
While levels of erm(B) were higher in those receiving long-term macrolide therapy and there was evidence of gene co-carriage with close contacts, there was no evidence that macrolide use increased the onward transmission risk to their close contacts. This study therefore addresses concerns that long-term macrolide therapy could promote the dissemination of transmissible macrolide resistance.

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