Dados do Trabalho

Título

Macrolide Resistance in Bordetella pertussis: Insights from Disk Diffusion Testing and Tentative Interpretative Ranges

Introdução

Macrolide antibiotics are used as first-line therapy for treating Bordetella pertussis infections but macrolide resistance in Asia is an ongoing threat. Test methods for macrolide resistance lack standardization for breakpoint interpretation. In 2021, a collaborative effort has worked to improve macrolide resistance detection in B. pertussis based on disk diffusion (DD) assay. 

Objetivo (s)

This abstract discusses using DD for macrolide susceptibility testing and proposes interpretative zone diameter ranges for addressing macrolide resistance in B.pertussis.

Material e Métodos

DD testing on 459 B. pertussis strains from Brazil and 357 from Mexico (2004-2023) involved 15 µg azithromycin, erythromycin, and clarithromycin-coated disks on Regan-Lowe plates. Susceptibility was defined as ≥40 mm inhibition zone. The absence of zones or bacterial growth after 3, 5, or 7 days indicated resistance. Strains also underwent Erythromycin Resistance PCR (ER-PCR) to detect the A2047G mutation associated with resistance. 

Resultados e Conclusão

The 10th percentile for erythromycin and azithromycin was 45 mm and 47 mm, respectively, with means of 54.5 mm and 47 mm. However, clarithromycin predominantly had smaller inhibition zone diameters, with 10th percentile and mean of 34 mm and 41 mm. ER-PCR confirmed the lack of mutation in all these isolates, and zone diameters remained stable after 3, 5, and 7 days of incubation. Among these strains, 51% exhibited inhibition zones below 40 mm for clarithromycin, with 46% falling between 38 mm and 46 mm. The 10th percentile data and the absence of the A2047G mutation support a provisional breakpoint of 32 mm or greater for clarithromycin susceptibility. In our study, B. pertussis isolates exhibiting inhibition zones greater than 40 mm may be considered susceptible to erythromycin; a comparable interpretation was also noted for azithromycin. However, this value is not suitable for clarithromycin since most of our isolates produced results that were less than 40 mm. According to our data, a breakpoint of 32 mm is proposed as a provisional cut-off value for clarithromycin. Initial macrolide susceptibility interpretation can be done after three days of incubation, with further incubation needed only to rule out resistant bacterial growth within the inhibition zones. Additional studies are necessary to fully validate the proposed breakpoints.

Palavras Chave

Macrolide resistance; B.pertussis; ER-PCR; breakpoints