RESUMEN
Macrolide resistance has been linked to the presence of a functional erythromycin ribosomal methylase (erm) gene in most species of pathogenic rapidly growing mycobacteria (RGM). For these Mycobacterium isolates, extended incubation in clarithromycin is necessary to determine macrolide susceptibility. In contrast, the absence of a detectable erm gene in isolates of M. chelonae, M. senegalense, and M. peregrinum and a nonfunctional erm gene in M. abscessus subsp. massiliense and 15% to 20% of M. abscessus subsp. abscessus isolates renders these species intrinsically macrolide susceptible. Not all RGM species have been screened for the presence of an erm gene, including the Mycobacterium mucogenicum group (M. mucogenicum, M. phocaicum, and M. aubagnense) and Mycobacterium immunogenum. A total of 356 isolates of these two pathogenic RGM taxa from two reference laboratories (A.R.U.P. Reference Laboratories and the Mycobacteria/Nocardia Laboratory at the University of Texas Health Science Center at Tyler) underwent clarithromycin susceptibility testing with readings at 3 to 5 days and 14 days. Only 13 of the 356 isolates had resistant clarithromycin MICs at initial extended MIC readings, and repeat values on all available isolates were ≤2 µg/ml. These studies suggest that these two additional RGM groups do not harbor functional erm genes and, like M. chelonae, do not require extended clarithromycin susceptibility testing. We propose to the Clinical Laboratory and Standards Institute that isolates belonging to these above-mentioned six rapidly growing mycobacterial groups based on molecular identification with no known functional erm genes undergo only 3 to 5 days of susceptibility testing (to exclude mutational resistance).
Asunto(s)
Antibacterianos/farmacología , Claritromicina/farmacología , Metiltransferasas/genética , Micobacterias no Tuberculosas/efectos de los fármacos , Micobacterias no Tuberculosas/genética , Humanos , Macrólidos/farmacología , Pruebas de Sensibilidad Microbiana , Infecciones por Mycobacterium/microbiología , Micobacterias no Tuberculosas/aislamiento & purificación , Estudios Retrospectivos , Factores de TiempoRESUMEN
The erm(41) gene causes inducible macrolide resistance in Mycobacterium abscessus but not Mycobacterium chelonae. erm(41) sequencing of 285 M. abscessus and 45 M. chelonae isolates was compared to 14-day susceptibility; agreement percentages were 98.9% and 100%, respectively. Extended incubation may not be necessary for M. chelonae, and the erm(41) genotype is a useful adjunct for M. abscessus.