title: In vitro selection of Staphylococcus aureus mutants resistant to tigecycline with intermediate susceptibility to vancomycin.
abstract: BACKGROUND
  Tigecycline (TIG) is an antibiotic belonging to the glycylcyclines class and appears to be a good choice to fight infections caused by Staphylococcus aureus. To date, TIG exhibits good activity against this microorganism. The aim of this work was to obtain in vitro mutants of S. aureus resistant to TIG and evaluate possible changes in their susceptibility patterns to other antibiotics.
  
  
  RESULTS
  Two mutants of S. aureus resistant to TIG (MIC = 16 µg/mL) were selected in vitro from clinical isolates of methicillin-resistant S. aureus. In both mutants, corresponding to different lineage (ST5 and ST239), an increase of efflux activity against TIG was detected. One mutant also showed a reduced susceptibility to vancomycin, corresponding to the VISA phenotype (MIC = 4 µg/mL), with a loss of functionality of the agr locus. The emergence of the VISA phenotype was accompanied by an increase in oxacillin and cefoxitin MICs.
  
  
  CONCLUSIONS
  This study demonstrates that, under selective pressure, the increase of efflux activity in S. aureus is one of the mechanisms that may be involved in the emergence of tigecycline resistance. The emergence of this phenotype may eventually be associated to changes in susceptibility to other antibiotics such oxacillin and vancomycin.
authors.affiliation: Facultad de Ciencias de la Salud, Universidad Adventista del Plata, 25 de mayo 99, Libertador San Martín, Entre Ríos, Argentina. invest5@uap.edu.ar.
authors.forename: Melina
authors.initials: M
authors.lastname: Herrera
authors.affiliation: Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Junín 956, Ciudad Autónoma de Buenos Aires, Argentina. sndigregorio@gmail.com.
authors.forename: Sabrina
authors.initials: S
authors.lastname: Di Gregorio
authors.affiliation: Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Junín 956, Ciudad Autónoma de Buenos Aires, Argentina. silvinafernandez23@gmail.com.
authors.forename: Silvina
authors.initials: S
authors.lastname: Fernandez
authors.affiliation: Facultad de Ciencias de la Salud, Universidad Adventista del Plata, 25 de mayo 99, Libertador San Martín, Entre Ríos, Argentina. grposse@gmail.com.
authors.forename: Graciela
authors.initials: G
authors.lastname: Posse
authors.affiliation: Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Junín 956, Ciudad Autónoma de Buenos Aires, Argentina. mmollera@ffyb.uba.ar.
authors.forename: Marta
authors.initials: M
authors.lastname: Mollerach
authors.affiliation: Facultad de Ciencias de la Salud, Universidad Adventista del Plata, 25 de mayo 99, Libertador San Martín, Entre Ríos, Argentina. jdiconza@gmail.com.|Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Junín 956, Ciudad Autónoma de Buenos Aires, Argentina. jdiconza@gmail.com.|Facultad de Bioquímica y Ciencias Biológicas, Universidad Nacional del Litoral, Ciudad Universitaria, Paraje "El Pozo", CC 242, Santa Fe, Argentina. jdiconza@gmail.com.
authors.forename: José
authors.initials: J
authors.lastname: Di Conza
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D024881:Drug Resistance, Bacterial; D006801:Humans; D008826:Microbial Sensitivity Tests; D008911:Minocycline / Q000031:analogs & derivatives* / Q000494:pharmacology; D009154:Mutation / Q000187:drug effects; D013203:Staphylococcal Infections / Q000382:microbiology*; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000235:genetics* / Q000378:metabolism; D000078304:Tigecycline; D014640:Vancomycin / Q000494:pharmacology*
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D014640:Vancomycin; D000078304:Tigecycline; D008911:Minocycline