title: Anti-microbial locks increase the prevalence of Staphylococcus aureus and antibiotic-resistant Enterobacter: observational retrospective cohort study.
abstract: 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.
  
  
  CONCLUSIONS
  AML decrease CR-BSI incidence, although proportions of S. aureus and anti-microbial-resistant Enterobacter are increased.
authors.affiliation: South West Thames Renal and Transplantation Unit, St. Helier Hospital, Carshalton, Surrey, UK. johndixon3@nhs.net
authors.forename: John J
authors.initials: JJ
authors.lastname: Dixon
authors.forename: Maggi
authors.initials: M
authors.lastname: Steele
authors.forename: A David
authors.initials: AD
authors.lastname: Makanjuola
mesh_terms: D058186:Acute Kidney Injury / Q000150:complications / Q000628:therapy; D000368:Aged; D016470:Bacteremia / Q000209:etiology / Q000517:prevention & control*; D016022:Case-Control Studies; D055499:Catheter-Related Infections / Q000188:drug therapy / Q000209:etiology; D002408:Catheters, Indwelling / Q000009:adverse effects*; D004352:Drug Resistance, Microbial / Q000187:drug effects*; D004754:Enterobacter / Q000187:drug effects*; D004756:Enterobacteriaceae Infections / Q000188:drug therapy / Q000453:epidemiology / Q000382:microbiology; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D015995:Prevalence; D011379:Prognosis; D006435:Renal Dialysis / Q000009:adverse effects*; D012189:Retrospective Studies; D013203:Staphylococcal Infections / Q000188:drug therapy / Q000453:epidemiology* / Q000382:microbiology; D013211:Staphylococcus aureus / Q000187:drug effects; D006113:United Kingdom / Q000453:epidemiology