Abstract
BackgroundLinezolid is an oxazolidinone antimicrobial regarded as a “last resort” antimicrobial, used typically for treatment of Gram-positive bacterial infections. It is acknowledged that prevalence of resistance to linezolid is increasing in Europe. In Ireland, a number of outbreaks of linezolid-resistant isolates have been reported, including an outbreak at the location for this study, the Intensive Care Unit (ICU) of University Hospital Limerick (UHL).MethodsThe Chromagar™ Lin-R selective medium was validated using a panel of linezolid-sensitive and linezolid-resistant strains. Subsequently, the prevalence exercise focused on a convenience sample of patients (n = 159) in critical care wards, ICU (n = 23) and High-Dependency Unit (HDU, n = 51), in addition to patients undergoing dialysis therapy (n = 77). Eight additional patients had specimens collected when attending more than one location. Growth on Chromagar™ Lin-R agar was followed by drug sensitivity testing by disc diffusion and minimum inhibitory concentration (MIC) testing.ResultsA validation exercise was performed on 23 isolates: seven target and sixteen non-target organisms. Isolates performed as intended (100% sensitivity, 100% specificity). For the prevalence study, of 398 tests, 40 resulted in growth of non-target organisms (specificity approx. 90%). A sole patient (1/159) was identified as colonized by a linezolid-resistant Staphylococcus epidermidis, a prevalence of 0.63%. Molecular investigation confirmed presence of the G2576T mutation in the 23S rRNA.ConclusionWhile this point prevalence study identified extremely low carriage of linezolid-resistant bacteria, it remains prudent to maintain vigilance as reports of outbreaks associated with linezolid-resistant S. epidermidis (LRSE) in European critical care units are increasing.
Highlights
Linezolid was the first oxazolidinone antimicrobial agent approved by the FDA, in 2000
University Hospital Limerick (UHL), a linezolid-resistant S. aureus harbouring the G2576T mutation was isolated from a cystic fibrosis patient in 2005 [9] while we reported the first cfr-mediated linezolid-resistant S. epidermidis outbreak in an Irish Intensive Care Unit (ICU), involving nine colonized or infected patients in 2013 [3]
A study by Egan et al [10] revealed enterococci in Irish hospitals exhibited high transmissibility, implicating optrA and poxtA genes. Subsequent to these reports, the Irish Health Protection Surveillance Centre recommended screening of individuals who are at risk for carriage of antimicrobial-resistant organisms [11] upon presentation at hospitals
Summary
Linezolid was the first oxazolidinone antimicrobial agent approved by the FDA, in 2000. University Hospital Limerick (UHL), a linezolid-resistant S. aureus harbouring the G2576T mutation was isolated from a cystic fibrosis patient in 2005 [9] while we reported the first cfr-mediated linezolid-resistant S. epidermidis outbreak in an Irish Intensive Care Unit (ICU), involving nine colonized or infected patients in 2013 [3]. A study by Egan et al [10] revealed enterococci in Irish hospitals exhibited high transmissibility, implicating optrA and poxtA genes Subsequent to these reports, the Irish Health Protection Surveillance Centre recommended screening of individuals who are at risk for carriage of antimicrobial-resistant organisms [11] upon presentation at hospitals. In Ireland, a number of outbreaks of linezolid-resistant isolates have been reported, including an outbreak at the location for this study, the Intensive Care Unit (ICU) of University Hospital Limerick (UHL). Conclusion While this point prevalence study identified extremely low carriage of linezolid-resistant bacteria, it remains prudent to maintain vigilance as reports of outbreaks associated with linezolid-resistant S. epidermidis (LRSE) in European critical care units are increasing
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