title: Evaluation of the in vitro activity of tigecycline against multiresistant Gram-positive cocci containing tetracycline resistance determinants.
abstract: This study was undertaken to test the in vitro activity of tigecycline against 117 clinically relevant Gram-positive pathogens and to correlate this activity with their resistance gene content. Overall, tigecycline showed a minimal inhibitory concentration (MIC) range of 0.015-0.5mg/L, able to inhibit potently all multiresistant streptococci, enterococci and MR staphylococci. Tigecycline was active against methicillin-resistant Staphylococcus aureus (MRSA) and enterococci, with MICs for 90% of the organisms (MIC(90)) of 0.25 mg/L and 0.12 mg/L, respectively, being more active than linezolid (MIC(90)=2 mg/L) and quinupristin/dalfopristin (MIC(90)=0.5 and 2-4 mg/L, respectively). Molecular characterisation of resistance determinants demonstrated the concomitant presence of different classes of genes: in particular, tet(M), erm(B) and erm(C) in Streptococcus agalactiae; tet(O), variably associated with different erm genes, in Streptococcus pyogenes; vanA, tet(M) and erm(B) in Enterococcus faecalis, and vanA and erm(B) in Enterococcus faecium. All the MRSA strains harboured SCCmec and erm genes and 50% possessed tet(K) with tet(M) genes. Staphylococcus epidermidis strains were only resistant to erythromycin. These results clearly demonstrate that tigecycline has a MIC(90) range of 0.015-0.5 mg/L both against tetracycline-susceptible and -resistant isolates carrying other resistance determinants, suggesting that this drug could play an important role in the treatment of infections caused by these multiresistant Gram-positive pathogens.
authors.affiliation: Department of Microbiology, University of Catania, Via Androne 81, 95124 Catania, Italy.
authors.forename: Sonia
authors.initials: S
authors.lastname: Borbone
authors.forename: Agnese
authors.initials: A
authors.lastname: Lupo
authors.forename: Maria Lina
authors.initials: ML
authors.lastname: Mezzatesta
authors.forename: Floriana
authors.initials: F
authors.lastname: Campanile
authors.forename: Maria
authors.initials: M
authors.lastname: Santagati
authors.forename: Stefania
authors.initials: S
authors.lastname: Stefani
mesh_terms: D000081:Acetamides / Q000494:pharmacology; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D024901:Drug Resistance, Multiple, Bacterial / Q000235:genetics*; D016983:Enterococcus / Q000187:drug effects* / Q000235:genetics; D005798:Genes, Bacterial; D006801:Humans; D000069349:Linezolid; D008826:Microbial Sensitivity Tests; D008911:Minocycline / Q000031:analogs & derivatives* / Q000494:pharmacology; D023303:Oxazolidinones / Q000494:pharmacology; D013210:Staphylococcus / Q000187:drug effects* / Q000235:genetics; D013291:Streptococcus / Q000187:drug effects* / Q000235:genetics; D013753:Tetracycline Resistance / Q000235:genetics*; D000078304:Tigecycline; D014769:Virginiamycin / Q000494:pharmacology
chemical_list: D000081:Acetamides; D000900:Anti-Bacterial Agents; D023303:Oxazolidinones; D014769:Virginiamycin; C062940:quinupristin-dalfopristin; D000078304:Tigecycline; D008911:Minocycline; D000069349:Linezolid