title: Absence of a functional erm gene in isolates of Mycobacterium immunogenum and the Mycobacterium mucogenicum group, based on in vitro clarithromycin susceptibility.
abstract: 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).
authors.affiliation: Mycobacteria/Nocardia Laboratory, The University of Texas Health Science Center at Tyler, Tyler, Texas, USA barbara.elliott@uthct.edu.
authors.forename: Barbara A
authors.initials: BA
authors.lastname: Brown-Elliott
authors.affiliation: Pathology Laboratories, A.R.U.P., Salt Lake City, Utah, USA.
authors.forename: Kimberly
authors.initials: K
authors.lastname: Hanson
authors.affiliation: Mycobacteria/Nocardia Laboratory, The University of Texas Health Science Center at Tyler, Tyler, Texas, USA.
authors.forename: Sruthi
authors.initials: S
authors.lastname: Vasireddy
authors.affiliation: Mycobacteria/Nocardia Laboratory, The University of Texas Health Science Center at Tyler, Tyler, Texas, USA.
authors.forename: Elena
authors.initials: E
authors.lastname: Iakhiaeva
authors.affiliation: Department of Pathology, Keck School of Medicine of USC, Los Angeles, California, USA.
authors.forename: Kevin A
authors.initials: KA
authors.lastname: Nash
authors.affiliation: Mycobacteria/Nocardia Laboratory, The University of Texas Health Science Center at Tyler, Tyler, Texas, USA.
authors.forename: Ravikiran
authors.initials: R
authors.lastname: Vasireddy
authors.affiliation: Mycobacteria/Nocardia Laboratory, The University of Texas Health Science Center at Tyler, Tyler, Texas, USA.
authors.forename: Nicholas
authors.initials: N
authors.lastname: Parodi
authors.affiliation: Mycobacteria/Nocardia Laboratory, The University of Texas Health Science Center at Tyler, Tyler, Texas, USA.
authors.forename: Terry
authors.initials: T
authors.lastname: Smith
authors.affiliation: Mycobacteria/Nocardia Laboratory, The University of Texas Health Science Center at Tyler, Tyler, Texas, USA.
authors.forename: Martha
authors.initials: M
authors.lastname: Gee
authors.affiliation: Mycobacteria/Nocardia Laboratory, The University of Texas Health Science Center at Tyler, Tyler, Texas, USA.
authors.forename: Anita
authors.initials: A
authors.lastname: Strong
authors.affiliation: Pathology Laboratories, A.R.U.P., Salt Lake City, Utah, USA.
authors.forename: Adam
authors.initials: A
authors.lastname: Barker
authors.affiliation: Pathology Laboratories, A.R.U.P., Salt Lake City, Utah, USA.
authors.forename: Samuel
authors.initials: S
authors.lastname: Cohen
authors.affiliation: Pathology Laboratories, A.R.U.P., Salt Lake City, Utah, USA.
authors.forename: Haleina
authors.initials: H
authors.lastname: Muir
authors.affiliation: Pathology Laboratories, A.R.U.P., Salt Lake City, Utah, USA.
authors.forename: E Susan
authors.initials: ES
authors.lastname: Slechta
authors.affiliation: Mycobacteria/Nocardia Laboratory, The University of Texas Health Science Center at Tyler, Tyler, Texas, USA.
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Wallace
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D017291:Clarithromycin / Q000494:pharmacology*; D006801:Humans; D018942:Macrolides / Q000494:pharmacology; D008780:Methyltransferases / Q000235:genetics*; D008826:Microbial Sensitivity Tests; D009164:Mycobacterium Infections / Q000382:microbiology; D009170:Nontuberculous Mycobacteria / Q000187:drug effects* / Q000235:genetics* / Q000302:isolation & purification; D012189:Retrospective Studies; D013997:Time Factors
chemical_list: D000900:Anti-Bacterial Agents; D018942:Macrolides; D008780:Methyltransferases; C035181:rRNA (adenosine-O-2'-)methyltransferase; D017291:Clarithromycin