Antimicrobial resistance of 100 serial gram-negative isolates in two intensive care units

To determine antimicrobial resistance pattern among gram-negative bacteria isolated from suspected sources of infections in patients hospitalized in two Intensive Care Units (ICUs) at Siriraj Hospital from September 1991 to December 1991, minimal inhibitory concentrations of one-hundred consecutive gram-negative isolates for various antimicrobials were performed using the microbroth dilution method. Of all gram-negative bacterial isolates, 25 per cent were Pseudomonas aeruginosa, 22 per cent Acinetobacter anitratus, 16 per cent Klebsiella pneumoniae, 12 per cent enterobacter, 8 per cent E.coli, 5 per cent non-fermenter, 4 per cent pseudomonas, 3 per cent arizona, 2 per cent A. lwoffii, 1 per cent Aeromonas hydrophila, 1 per cent Aeromonas hydrophila, 1 per cent Proteus rettgeri, and 1 per cent shigella. The in vitro MIC study revealed that 50, 48, 43, 61, 59, 34, 47, 52, 31, 15 per cent of gram-negative isolates were resistant to gentamicin, tobramycin, amikacin, cefotaxime, ceftriaxone, ceftazidime, aztreonam, piperacillin, ciprofloxacin and imipenem respectively. In addition, 64 and 71 per cent of the isolates were resistant to aminoglycosides and cephalosporins being used in the same patients 48 hours before cultures were obtained respectively. The possible spread of resistant gram-negative isolates by cross contamination was not evident by looking at MIC co-variation in sequential isolates of P. aeruginosa. It was concluded that antimicrobial resistance was highly prevalent among gram-negative bacteria isolated from patients already hospitalized in the ICUs. Potent antimicrobials such as imipenem, newer fluoro-quinolones, ceftazidime and amikacin, are often needed for therapy of serious gram-negative bacterial infections in the ICUs.