The role of surveillance cultures in the prediction of susceptibility patterns of Gram-negative bacilli in the intensive care unit.

Surveillance cultures may detect colonisation with drug-resistant Gram-negative bacteria and can be hypothesised to guide appropriate initial antibiotic treatment for intensive care unit (ICU) patients. We investigated the microbiological data of 228 episodes of nosocomial bloodstream infection (BSI) due to Gram-negative bacteria in an ICU in which piperacillin/tazobactam or meropenem was used empirically for serious infections, to evaluate the contribution of surveillance cultures to an appropriate choice of initial antibiotic therapy. Surveillance cultures were taken in advance of BSI in 218 (95.6%) of 228 episodes. Concordant organisms with identical identification and susceptibilities were found in prior surveillance cultures and subsequent blood cultures in 65 (29.8%) of 218 episodes. Surveillance cultures predicted resistance in 52.9% and 51.4% of BSIs caused by resistant pathogens to piperacillin/tazobactam and meropenem, respectively. The negative predictive value of surveillance cultures negative for a resistant organism also exceeded 90% for piperacillin/tazobactam and meropenem. Given that the overall resistant rates of BSI pathogens of our study were 11.3% to piperacillin/tazobactam and 16.4% to meropenem, surveillance cultures in our setting may provide important information on the probability of drug resistance of the causative pathogens and some utility in aiding empiric antibiotic therapy for ICU patients who subsequently develop BSI.