Antimicrobial co-resistance patterns of gram-negative bacilli isolated from bloodstream infections: a longitudinal epidemiological study from 2002–2011
Background: Increasing multidrug resistance in gram-negative bacilli (GNB) infections poses a serious threat to
public health. Few studies have analyzed co-resistance rates, defined as an antimicrobial susceptibility profile in a
subset already resistant to one specific antibiotic. The epidemiologic and clinical utility of determining co-resistance
rates are analyzed and discussed.
Methods: A 10-year retrospective study from 2002–2011 of bloodstream infections with GNB were analyzed from
three hospitals in Greater Vancouver, BC, Canada. Descriptive statistics were calculated for antimicrobial resistance
and co-resistance. Statistical analysis further described temporal trends of antimicrobial resistance, correlations of
resistance between combinations of antimicrobials, and temporal trends in co-resistance patterns.
Results: The total number of unique blood stream isolates of GNB was 3280. Increasing resistance to individual
antimicrobials was observed for E. coli, K. pneumoniae, K. oxytoca, E. cloacae, and P. aeruginosa. Ciprofloxacin
resistance in E. coli peaked in 2006 at 40% and subsequently stabilized at 29% in 2011, corresponding to decreasing
ciprofloxacin usage after 2007, as assessed by defined daily dose utilization data. High co-resistance rates were
observed for ceftriaxone-resistant E. coli with ciprofloxacin (73%), ceftriaxone-resistant K. pneumoniae with
trimethoprim-sulfamethoxazole (83%), ciprofloxacin-resistant E. cloacae with ticarcillin-clavulanate (91%), and
piperacillin-tazobactam-resistant P. aeruginosa with ceftazidime (83%).
Conclusions: Increasing antimicrobial resistance was demonstrated over the study period, which may partially be
associated with antimicrobial consumption. The study of co-resistance rates in multidrug resistant GNB provides
insight into the epidemiology of resistance acquisition, and may be used as a clinical tool to aid prescribing empiric
For the full version of the article click here: Antimicrobial co-resistance patterns of gram-negative bacilli isolated from bloodstream infections: a longitudinal epidemiological study from 2002–2011