title: Virulence of vancomycin-resistant Enterococcus faecium according to linezolid resistance and clinical outbreak status.
abstract: Assessing clinical virulence differences between vancomycin-resistant Enterococcus faecium (VREF) strains resistant to linezolid (LRVRE) and linezolid-susceptible VRE (LSVRE) strains is difficult due to confounding patient variables. Galleria mellonella is a validated host interaction model allowing straightforward organism virulence assessment. The objective of this study was to assess the virulence of VREF in G. mellonella according to linezolid resistance and clinical outbreak status. A genetically related pair of VREF strains with and without genotypically confirmed linezolid resistance was selected for analysis. Additionally, six strains of LSVRE and two strains of LRVRE were selected according to epidemiologic outbreak status. Mortality of G. mellonella was assessed daily over a 5-day period and analyzed using Kaplan-Meier survival curves and log rank tests. Linezolid resistance did not have a significant effect on G. mellonella mortality in the genetically related pair (P = 0.93). There was no significant difference in mortality over time between strains (non-outbreak [i.e., no patient transmissions were recorded] [n = 2] versus outbreak [i.e., transmission occurred between 3 or more patients in a period of 30 days] [n = 6], P = 0.84; extensive transmission [i.e., the isolate was transmitted between at least 80 patients] [n = 2] versus limited transmission [i.e., the isolate was transmitted between fewer than 10 patients] [n = 4], P = 0.78). These results suggest that patients infected with LRVRE or outbreak strains of VREF are at no greater risk of poor outcomes mediated by organism virulence than those infected with LSVRE or non-outbreak strains.
authors.affiliation: Midwestern University, Downers Grove, Illinois, USA.
authors.forename: Milena
authors.initials: M
authors.lastname: McLaughlin
authors.forename: Michael
authors.initials: M
authors.lastname: Malczynski
authors.forename: Chao
authors.initials: C
authors.lastname: Qi
authors.forename: Grace
authors.initials: G
authors.lastname: Barajas
authors.forename: Jordan
authors.initials: J
authors.lastname: Radetski
authors.forename: Teresa
authors.initials: T
authors.lastname: Zembower
authors.forename: Marc H
authors.initials: MH
authors.lastname: Scheetz
mesh_terms: D000081:Acetamides / Q000494:pharmacology*; D000818:Animals; D002641:Chicago / Q000453:epidemiology; D004195:Disease Models, Animal; D004196:Disease Outbreaks; D052978:Disk Diffusion Antimicrobial Tests; D016984:Enterococcus faecium / Q000187:drug effects* / Q000235:genetics / Q000472:pathogenicity*; D016908:Gram-Positive Bacterial Infections / Q000188:drug therapy / Q000453:epidemiology*; D006746:Hospital Bed Capacity, 500 and over; D006801:Humans; D053208:Kaplan-Meier Estimate; D000069349:Linezolid; D009036:Moths / Q000382:microbiology; D023303:Oxazolidinones / Q000494:pharmacology*; D013997:Time Factors; D014640:Vancomycin / Q000494:pharmacology; D020713:Vancomycin Resistance
chemical_list: D000081:Acetamides; D023303:Oxazolidinones; D014640:Vancomycin; D000069349:Linezolid