Anti-microbial locks increase the prevalence of Staphylococcus aureus and antibiotic-resistant Enterobacter: observational retrospective cohort study.

BACKGROUND Anti-microbial lock solutions (AML), in conjunction with systemic antibiotics, may successfully treat tunnelled haemodialysis catheter-related bloodstream infections (CR-BSI). It is unknown whether AML promote anti-microbial resistance. METHODS This is a retrospective cohort study of all CR-BSI (2003-2006) in our dialysis unit. Controls (n = 265) were treated with systemic vancomycin and gentamicin. In addition to the systemic antibiotics, the study group (n = 662) received AML containing vancomycin and gentamicin during inter-dialytic periods. Antibiotic sensitivity/resistance profiles of all organisms were analysed. Changes in the incidence of infection (chi-square test) and resistant organisms (Fisher's exact test) were calculated. RESULTS The incidence of CR-BSI decreased from 8.50/1000 catheter days (controls) to 3.80 (study group; P < 0.0001), and the incidence of relapses decreased (P = 0.0027). The number needed to treat to prevent subsequent bacteraemia using an AML adjunct is 3 ± 0.4. The proportion of Gram-positive cultures increased (P < 0.0001), including Staphylococcus aureus (P = 0.03), but the proportion of methicillin-resistant S. aureus (P = 0.87) and vancomycin resistance (P = 0.90) did not. Increased gentamicin resistance (P < 0.0001) and ciprofloxacin resistance (P = 0.04) were observed in Gram-negative cultures. Gentamicin resistance [relative risk (RR) > 15.29; P < 0.0001] and ciprofloxacin resistance (RR = 6; P = 0.007) increased in Enterobacter species, but not Pseudomonas or Escherichia coli species. CONCLUSION AML decrease CR-BSI incidence, although proportions of S. aureus and anti-microbial-resistant Enterobacter are increased.