OBJECTIVES: Some clinical isolates of Mycobacterium fortuitum are naturally resistant to macrolides, e.g. clarithromycin. Thus, the aim of this study was to identify the gene(s) conferring this resistance. METHODS: M. fortuitum ATCC 6841T DNA libraries were screened for plasmids that complemented the macrolide-susceptible phenotype of Mycobacterium smegmatis variant ermKO4 [erm(38)-negative]. Macrolide-resistant M. smegmatis transformants were selected on agar containing 128 mg/L erythromycin. RESULTS: Genetic complementation identified an M. fortuitum rRNA methylase gene, termed erm(39), 69% identical to erm(38) of M. smegmatis. In addition, erm(39) was found to be in the same chromosomal location as erm(38) in their respective hosts. Like erm(38), erm(39) conferred resistance (MIC >128 mg/L) to macrolide-lincosamide (ML) agents, but not to streptogramin B. Analysis of erm gene expression in M. fortuitum showed that ML agents increased erm(39) RNA levels, reaching a steady state level approximately 20-fold higher than baseline. Screening of 32 M. fortuitum clinical isolates by PCR showed that all were positive for erm(39), irrespective of clarithromycin susceptibility. A majority of clarithromycin-susceptible (MIC < or = 2 mg/L) isolates were postulated to carry a disabled erm(39) gene as they had a GTG-->CTG mutation in the putative initiation codon of the erm(39) gene. CONCLUSIONS: The similarity of the erm genes of M. smegmatis and M. fortuitum suggests that they were inherited from a common ancestor. Although the clinical impact of erm(39) on the therapeutic utility of clarithromycin is unclear, induction of this gene is consistent with the trailing end-points commonly seen during susceptibility testing of M. fortuitum isolates against macrolides.
OBJECTIVES: Some clinical isolates of Mycobacterium fortuitum are naturally resistant to macrolides, e.g. clarithromycin. Thus, the aim of this study was to identify the gene(s) conferring this resistance. METHODS:M. fortuitumATCC 6841T DNA libraries were screened for plasmids that complemented the macrolide-susceptible phenotype of Mycobacterium smegmatis variant ermKO4 [erm(38)-negative]. Macrolide-resistant M. smegmatis transformants were selected on agar containing 128 mg/L erythromycin. RESULTS: Genetic complementation identified an M. fortuitum rRNA methylase gene, termed erm(39), 69% identical to erm(38) of M. smegmatis. In addition, erm(39) was found to be in the same chromosomal location as erm(38) in their respective hosts. Like erm(38), erm(39) conferred resistance (MIC >128 mg/L) to macrolide-lincosamide (ML) agents, but not to streptogramin B. Analysis of erm gene expression in M. fortuitum showed that ML agents increased erm(39) RNA levels, reaching a steady state level approximately 20-fold higher than baseline. Screening of 32 M. fortuitum clinical isolates by PCR showed that all were positive for erm(39), irrespective of clarithromycin susceptibility. A majority of clarithromycin-susceptible (MIC < or = 2 mg/L) isolates were postulated to carry a disabled erm(39) gene as they had a GTG-->CTG mutation in the putative initiation codon of the erm(39) gene. CONCLUSIONS: The similarity of the erm genes of M. smegmatis and M. fortuitum suggests that they were inherited from a common ancestor. Although the clinical impact of erm(39) on the therapeutic utility of clarithromycin is unclear, induction of this gene is consistent with the trailing end-points commonly seen during susceptibility testing of M. fortuitum isolates against macrolides.
Authors: F Schlünzen; R Zarivach; J Harms; A Bashan; A Tocilj; R Albrecht; A Yonath; F Franceschi Journal: Nature Date: 2001-10-25 Impact factor: 49.962
Authors: Richard J Wallace; Barbara A Brown-Elliott; Leslie Hall; Glenn Roberts; Rebecca W Wilson; Linda B Mann; Christopher J Crist; Sher H Chiu; Robbie Dunlap; Maria J Garcia; J Todd Bagwell; Kenneth C Jost Journal: J Clin Microbiol Date: 2002-08 Impact factor: 5.948
Authors: Kevin A Nash; Nadya Andini; Yansheng Zhang; Barbara A Brown-Elliott; Richard J Wallace Journal: Antimicrob Agents Chemother Date: 2006-10 Impact factor: 5.191
Authors: Barbara A Brown-Elliott; Kimberly Hanson; Sruthi Vasireddy; Elena Iakhiaeva; Kevin A Nash; Ravikiran Vasireddy; Nicholas Parodi; Terry Smith; Martha Gee; Anita Strong; Adam Barker; Samuel Cohen; Haleina Muir; E Susan Slechta; Richard J Wallace Journal: J Clin Microbiol Date: 2015-01-07 Impact factor: 5.948