The usefulness of the serum bactericidal test in orthopedic infections

Intraoperative Bacterial Contamination and Activity of Different Antimicrobial Prophylaxis Regimens in Primary Knee and Hip Replacement

Surgical antimicrobial prophylaxis (SAP) is important for the prevention of prosthetic joint infections (PJIs) and must be effective against the microorganisms most likely to contaminate the surgical site. Our aim was to compare different SAP regimens (cefazolin, cefuroxime, or vancomycin, alone or combined with gentamicin) in patients undergoing total knee (TKA) and hip (THA) arthroplasty. In this preclinical exploratory analysis, we analyzed the results of intraoperative sample cultures, the ratio of plasma antibiotic levels to the minimum inhibitory concentrations (MICs) for bacteria isolated at the surgical wound and ATCC strains, and serum bactericidal titers (SBT) against the same microorganisms. A total of 132 surgical procedures (68 TKA, 64 THA) in 128 patients were included. Cultures were positive in 57 (43.2%) procedures (mostly for coagulase-negative staphylococci and Cutibacterium spp.); the rate was lower in the group of patients receiving combination SAP (adjusted OR 0.475, CI95% 0.229-0.987). The SAP regimens evaluated achieved plasma levels above the MICs in almost all of intraoperative isolates (93/94, 98.9%) and showed bactericidal activity against all of them (SBT range 1:8-1:1024), although SBTs were higher in patients receiving cefazolin and gentamicin-containing regimens. The potential clinical relevance of these findings in the prevention of PJIs remains to be determined.

Release of gentamicin and vancomycin from preformed spacers in infected total hip arthroplasties: measurement of concentrations and inhibitory activity in patients' drainage fluids and serum

Gentamicin (G) and vancomycin (V) concentrations in drainage fluids obtained from patients during the first 24 hours after implantation of antibiotic-loaded polymethylmethacrylate (PMMA) spacers in two-stage revision of infected total hip arthroplasty were studied. The inhibitory activity of drainage fluids against different multiresistant clinical isolates was investigated as well. Seven hips were treated by implantation of industrial G-loaded spacers. Vancomycin was added by manually mixing with PMMA bone cement. Serum and drainage fluid samples were collected 1, 4, and 24 hours after spacer implantation. Antibiotics concentrations and drains bactericidal titer of combination were determined against multiresistant staphylococcal strains. The release of G and V from PMMA cement at the site of infection was prompt and effective. Serum levels were below the limit of detection. The local release kinetics of G and V from PMMA cement was similar, exerting a pronounced, combined inhibitory effect in the implant site. The inhibitory activity of drainage fluids showed substantial intersubject variability related to antibiotic concentrations and differed according to the pathogens tested. Gentamicin and vancomycin were released from temporary hip spacers at bactericidal concentrations, and their use in combination exerted strong inhibition against methicillin-resistant S. aureus and Coagulase Negative Staphylococci strains.

The bactericidal activity of gatifloxacin in plasma and urine

OBJECTIVE: To investigate the bactericidal activity of gatifloxacin in serum and urine against relevant pathogens. METHODS: Serum and urine samples obtained in a single rising dose pharmacokinetic study were investigated for bactericidal activity. The doses employed were placebo, and 200, 400, 600 and 800 mg of gatifloxacin. RESULTS: The titers obtained reflected the dose and susceptibility of the pathogen. In serum a titer of greater-than-or-equal1:8 was observed for Escherichia coli for >24 h after 400 mg; for Staphylococcus aureus and Acinetobacter baumanii the titer was greater-than-or-equal1:8 for between 12--24 h after 600 mg; for Serratia marcescens it was greater-than-or-equal1:8 for >12 h following 800 mg; and for Streptococcus pneumoniae it was greater-than-or-equal1:8 for 8 h following 800 mg. In urine, the titers were greater, and for Escherichia coli, Staphylococcus saprophyticus, Proteus mirabilis and Enterococcus faecalis the titer was >1:8 for 12--24 h after 200 mg and for 24--36 h after a 400-mg dose. Pseudomonas aeruginosa demonstrated a titer of >1:8 for 18--24 h following 600 mg. CONCLUSIONS: These data suggest that gatifloxacin should be efficacious for a wide range of systemic and urinary tract infections.