Microbiology of infected arthroplasty: implications for empiric peri-operative antibiotics.

PURPOSE: To classify the spectrum and antibiotic susceptibility of bacteria isolated from infected hip and knee arthroplasty specimens, and to recommend appropriate empiric peri-operative antibiotics.
METHODS: From January 1999 to August 2006, specimens from revision hip and knee arthroplasties (with or without suspected infection) were routinely collected for identifying possible organisms and their susceptibility patterns. During the period, 147 patients had positive specimens yielding 248 micro-organisms (from 195 tissue specimens, 43 fluid specimens, and 10 swabs). 140 isolates were from hips and 108 from knees.
RESULTS: Most isolates were Gram-positive; their distribution was similar in hip and knee specimens. Of the 248 micro-organisms isolated, Staphylococcus was the most common genus encountered (131, 53%), followed by Gram-negative isolates (24%). 88% of Gram-negative organisms were detected within 48 hours of inoculation and 94% of Gram-positive organisms within 96 hours. Overall, 46% of isolates were susceptible to cephalothin. Only 35% of coagulase-negative staphylococci were sensitive to cephalothin. No Gram-positive vancomycin resistance was encountered.
CONCLUSION: Empiric prophylactic antibiotics for revision hip and knee arthroplasties should include vancomycin to cover Gram-positive organisms and gentamicin for most Gram-negative bacteria.