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  Discussion on Scientific Report: Growing Resistance to Antibiotics
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DrO

Posted on Friday, Sep 2, 2016 - 12:11 pm:

Here is a discouraging report of growing resistance of Rhodococcus to some of our commonly used antibiotics. Knowledge of local resistance patterns could be essential for proper early selection of antimicrobial treatment. The best place to get this information would be your local and state labs. The article lists alternative antibiotics that could be considered.
DrO

{Dec;70(12):3184-90. doi: 10.1093/jac/dkv279. Epub 2015 Sep 16.

Novel transferable erm(46) determinant responsible for emerging macrolide resistance in Rhodococcus equi.

Anastasi E1, Giguère S2, Berghaus LJ3, Hondalus MK4 , Willingham-Lane JM4, MacArthur I1, Cohen ND5, Roberts MC6, Vazquez-Boland JA7.

Author information:
1Microbial Pathogenesis Unit, School of Biomedical Sciences and The Roslin Institute, University of Edinburgh, Edinburgh, UK.
2Department of Large Animal Medicine, University of Georgia, Athens, GA, USA.
3Department of Large Animal Medicine, University of Georgia, Athens, GA, USA.
4Department of Infectious Diseases, University of Georgia, Athens, GA, USA.
5Department of Large Animal Clinical Sciences, Texas A&M University, College Station, TX, USA.
6Department of Environmental and Occupational Health Sciences, School of Public Health, University of Washington, Seattle, WA, USA.
7Microbial Pathogenesis Unit, School of Biomedical Sciences and The Roslin Institute, University of Edinburgh, Edinburgh, UK Grupo de Patogenómica Bacteriana, Facultad de Veterinaria, Universidad de Léon, Léon, Spain.

OBJECTIVES:
The objective of this study was to identify the molecular mechanism of macrolide resistance in the actinomycete Rhodococcus equi, a major equine pathogen and zoonotic agent causing opportunistic infections in people.

METHODS:
Macrolide-resistant (n?=?62) and macrolide-susceptible (n?=?62) clinical isolates of R. equi from foals in the USA were studied. WGS of 18 macrolide-resistant and 6 macrolide-susceptible R. equi was performed. Representative sequences of all known macrolide resistance genes identified to date were used to search the genome assemblies for putative homologues. PCR was used to screen for the presence of the identified resistance determinant in the rest of the isolates. Mating experiments were performed to verify mobility of the gene.

RESULTS:
A novel erm gene, erm(46), was identified in all sequenced resistant isolates, but not in susceptible isolates. There was complete association between macrolide resistance and the presence of erm(46) as detected by PCR screening of all 124 clinical isolates of R. equi. Expression of erm(46) in a macrolide-susceptible strain of R. equi induced high-level resistance to macrolides, lincosamides and streptogramins B, but not to other classes of antimicrobial agents. Transfer of erm(46) to macrolide-susceptible R. equi was confirmed. The transfer frequency ranged from 3?×?10(-3) to 1?×?10(-2).

CONCLUSIONS:
This is the first molecular characterization of resistance to macrolides, lincosamides and streptogramins B in R. equi. Resistance was due to the presence of a novel erm(46) gene mobilizable likely by conjugation, which has spread among equine isolates of R. equi in the USA.}
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