title: High vancomycin MICs within the susceptible range in Staphylococcus aureus bacteraemia isolates are associated with increased cell wall thickness and reduced intracellular killing by human phagocytes.
abstract: Vancomycin minimum inhibitory concentrations (MICs) at the upper end of the susceptible range for Staphylococcus aureus have been associated with poor clinical outcomes of bloodstream infections. We tested the hypothesis that high vancomycin MICs in S. aureus bacteraemia isolates are associated with increased cell wall thickness and suboptimal bacterial internalisation or lysis by human phagocytes. In total, 95 isolates were evaluated. Original vancomycin MICs were determined by Etest. The susceptibility of S. aureus isolates to killing by phagocytes was assessed in a human whole blood assay. Internalisation of bacterial cells by phagocytes was investigated by flow cytometry. Cell wall thickness was evaluated by transmission electron microscopy. Genotypic analysis of S. aureus isolates was performed using a DNA microarray system. Vancomycin MICs were significantly higher (P=0.006) in isolates that were killed suboptimally (killing index <60%) compared with those killed efficiently (killing index >70%) and tended to correlate inversely (P=0.08) with the killing indices. Isolates in both killing groups were internalised by human neutrophils and monocytes with comparable efficiency. The cell wall was significantly thicker (P=0.03) in isolates in the low killing group. No genotypic differences were found between the isolates in both killing groups. In summary, high vancomycin MICs in S. aureus bacteraemia isolates were associated with increased cell wall thickness and reduced intracellular killing by phagocytes.
authors.affiliation: Microbiology Service, Hospital Clínico Universitario de Valencia, Fundación INCLIVA, Valencia, Spain.
authors.forename: Rocío
authors.initials: R
authors.lastname: Falcón
authors.affiliation: Department of Microbiology, Faculty of Pharmacy, University of Valencia, Valencia, Spain.
authors.forename: Alba
authors.initials: A
authors.lastname: Martínez
authors.affiliation: Microbiology Service, Hospital Clínico Universitario de Valencia, Fundación INCLIVA, Valencia, Spain.
authors.forename: Eliseo
authors.initials: E
authors.lastname: Albert
authors.affiliation: Microbiology Service, Hospital Clínico Universitario de Valencia, Fundación INCLIVA, Valencia, Spain.
authors.forename: Silvia
authors.initials: S
authors.lastname: Madrid
authors.affiliation: Unit of Infectious Diseases, Hospital Clínico Universitario de Valencia, Fundación INCLIVA, Valencia, Spain.
authors.forename: Rosa
authors.initials: R
authors.lastname: Oltra
authors.affiliation: Microbiology Service, Hospital Clínico Universitario de Valencia, Fundación INCLIVA, Valencia, Spain.
authors.forename: Estela
authors.initials: E
authors.lastname: Giménez
authors.affiliation: Centro de Investigación Príncipe Felipe, Valencia, Spain.
authors.forename: Mario
authors.initials: M
authors.lastname: Soriano
authors.affiliation: Microbiology Service, Hospital Clínico Universitario de Valencia, Fundación INCLIVA, Valencia, Spain.
authors.forename: Víctor
authors.initials: V
authors.lastname: Vinuesa
authors.affiliation: Department of Microbiology, Faculty of Pharmacy, University of Valencia, Valencia, Spain.
authors.forename: Daniel
authors.initials: D
authors.lastname: Gozalbo
authors.affiliation: Department of Microbiology, Faculty of Biological Sciences, University of Valencia, Valencia, Spain.
authors.forename: María Luisa
authors.initials: ML
authors.lastname: Gil
authors.affiliation: Microbiology Service, Hospital Clínico Universitario de Valencia, Fundación INCLIVA, Valencia, Spain; Department of Microbiology, School of Medicine, University of Valencia, Valencia, Spain. Electronic address: david.navarro@uv.es.
authors.forename: David
authors.initials: D
authors.lastname: Navarro
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D016470:Bacteremia / Q000382:microbiology*; D002473:Cell Wall / Q000648:ultrastructure*; D004705:Endocytosis; D005434:Flow Cytometry; D060005:Genotyping Techniques; D006801:Humans; D046228:Microarray Analysis; D008826:Microbial Sensitivity Tests; D050296:Microbial Viability; D010586:Phagocytes / Q000276:immunology* / Q000382:microbiology; D013203:Staphylococcal Infections / Q000382:microbiology*; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000276:immunology / Q000302:isolation & purification / Q000648:ultrastructure; D014640:Vancomycin / Q000494:pharmacology*
chemical_list: D000900:Anti-Bacterial Agents; D014640:Vancomycin
keywords: Cell wall thickness; Human phagocytes; Intracellular killing; Minimum inhibitory concentration (MIC); Staphylococcus aureus; Vancomycin