[Analyses of microbiology and antibiotic susceptibility in prosthetic knee infections]

To explore the microbiological etiology of prosthetic knee infections during two-staged revision and analyze antibiotic susceptibility of bacteria so as to provide clinical recommendations for empiric antibiotic therapy.

A retrospective review was performed for 78 hospitalized patients for prothetic knee infections undergoing two-staged revision between January 1, 2007 and February 28, 2014.Suspicious intra-operative tissues were collected and cultured. Microbiological data sets and antibiotic susceptibility of bacteria were analyzed.

Micro-organisms were isolated from 65 patients. The negative culture rate was 16.7%. The most common genus encountered was Gram-positive isolates (75.7%), followed by Gram-negative isolates (20.5%) and fungi isolates (2.7%). Polymicrobialinfections accounted for 15.4% of patients. The most common causative organism of infection was coagulase-negative staphylococci (46.6%) and followed by Staphylococcus aureus (20.5%). The detection rate of methicillin-resistant staphylococcus(MRS) was 34.3% (25/73) and it accounted for 47.5% of staphylococcus.Gram-negative isolates were dominated by Escherichia coli (4/15) and Acinetobacter baumannii (4/15). All A.baumanniiscame from polymicrobial infection. Coagulase-negative staphylococci and A. baumannii were the most common causative organisms of polymicrobial infection. The results of antibiotic susceptibility showed cefazolin and cefuroxime were poorly susceptible to isolates. The drug resistance rates were 43.5% and 53.6%.Some third or fourth generation cephalosporins also have problems of bacterial resistance.Some antibiotics such as vancomycin, linezolid, imipenem, rifampin, cefoperazone/sulbactam and levofloxacin had high rates of drug sensitivity.

Most infections are caused by staphylococci. The proportion of isolated MRS is high.Empiric prophylacticantibiotics therapy may include vancomycin and cefoperazone/sulbactam to cover Gram-positive and Gram-negative organisms.Empiric therapeutic antibiotics therapy includes vancomycin and carbapenems. After the results of antibiotic susceptibility, antibiotics should be timely adjusted.