title: Virulence-suppressing effects of linezolid on methicillin-resistant Staphylococcus aureus: possible contribution to early defervescence.
abstract: In the present study, immunomodulatory effects of linezolid (LZD) on methicillin-resistance Staphylococcus aureus (MRSA) infections were evaluated. We have retrospectively reviewed treatment effects of LZD on 52 patients with severe MRSA infections. Sixty-four percent of the febrile patients demonstrated significant defervescence within 3 days, despite the presence of positive culture results. We speculated that this finding might be due to early anti-inflammatory effects of LZD, and to investigate this further we initiated in vivo experiments using mice MRSA pneumonia models. Mice were treated with either LZD or vancomycin (VCM) immediately after intranasal administration of MRSA. Bacterial numbers and levels of inflammatory cytokines in the lungs were determined. Although the bacterial burden in the lungs was not apparently different between the two groups, LZD but not VCM treatment significantly reduced induction of inflammatory cytokines in the lungs (P < 0.05). To evaluate whether this anti-inflammatory response was due to suppression of virulence factor expression, filter-sterilized supernatants of MRSA incubated in broth overnight with sub-MICs of LZD were subcutaneously administered to mice. To clarify whether LZD possesses direct host-modulating activity, cytokine responses to the supernatants were examined in mice pretreated with LZD. Interestingly, MRSA solutions prepared in the presence of sub-MICs of LZD revealed significant suppression of interleukin 6 (IL-6) in a dose-dependent manner (P < 0.05), but pretreatment of mice with LZD revealed no changes in cytokines. These findings suggest that sub-MICs of LZD might suppress virulence factors of MRSA, which may be associated with a reduction in endogenous pyrogens. These data may explain at least in part early defervescence observed in LZD-treated individuals.
authors.affiliation: Department of Infection Control, Toho University Omori Medical Center, Tokyo, Japan. sadako@med.toho-u.ac.jp
authors.forename: Sadako
authors.initials: S
authors.lastname: Yoshizawa
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Tateda
authors.forename: Tomoo
authors.initials: T
authors.lastname: Saga
authors.forename: Yoshikazu
authors.initials: Y
authors.lastname: Ishii
authors.forename: Keizo
authors.initials: K
authors.lastname: Yamaguchi
mesh_terms: D000081:Acetamides / Q000494:pharmacology*; D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D015169:Colony Count, Microbial; D016207:Cytokines / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D006801:Humans; D015850:Interleukin-6 / Q000096:biosynthesis; D000069349:Linezolid; D008168:Lung / Q000378:metabolism; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects* / Q000472:pathogenicity*; D051379:Mice; D008807:Mice, Inbred BALB C; D008826:Microbial Sensitivity Tests; D023303:Oxazolidinones / Q000494:pharmacology*; D011749:Pyrogens / Q000378:metabolism; D018805:Sepsis / Q000188:drug therapy / Q000382:microbiology; D013203:Staphylococcal Infections / Q000188:drug therapy / Q000382:microbiology; D014409:Tumor Necrosis Factor-alpha / Q000096:biosynthesis; D014774:Virulence / Q000187:drug effects; D037521:Virulence Factors / Q000037:antagonists & inhibitors / Q000096:biosynthesis; D000093242:Interleukin-6 Inhibitors
chemical_list: D000081:Acetamides; D000900:Anti-Bacterial Agents; D016207:Cytokines; D015850:Interleukin-6; D000069349:Linezolid; D023303:Oxazolidinones; D011749:Pyrogens; D014409:Tumor Necrosis Factor-alpha; D037521:Virulence Factors; D000093242:Interleukin-6 Inhibitors