Michael Hornsey - Tigecycline resistance in Serratia marcescens associated with up-regulation of the SdeXY-HasF efflux system also active against ciprofloxacin and cefpirome

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  Hornsey, Michael, Ellington, Matthew J., Doumith, Michel, Hudson,   Sue, Livermore, David M., Woodford, Neil Journal of   Antimicrobial Chemotherapy 2010 65  (3 ) 479 -482

  Abstract: Objectives Efflux by RND-type   transporters is known to confer resistance to tigecycline in   several Enterobacteriaceae species and we examined the potential   of this mechanism in Serratia marcescens using a clinical isolate   and laboratory-selected mutants.Methods Expression of RND-type   efflux pump genes was analysed by real-time RT–PCR. Laboratory   mutants were selected by exposure to either tigecycline or   tetracycline in vitro. Efflux pump genes were inactivated by   suicide plasmids containing the R6Kγ origin of   replication.Results Higher tigecycline MICs correlated with   elevated expression of the RND-type efflux pump genes sdeXY.   Inactivation of sdeY or the outer membrane component gene hasF   reduced MICs of tigecycline, tetracycline, ciprofloxacin and   cefpirome to below those for strain NCTC 10211. A   tetracycline-selected laboratory mutant also showed increases in   sdeXY expression and tigecycline MIC.Conclusions Up-regulation of   endogenous SdeXY–HasF-mediated efflux is associated with   tigecycline resistance in S. marcescens along with MIC rises for   tetracycline, ciprofloxacin and cefpirome. Inactivation of this   efflux system reduced MICs of those compounds to below those for   strain NCTC 10211.

  Address (URL): http://jac.oxfordjournals.org/content/65/3/479.abstract