Microbiology of postoperative infections

Surgical infections, accounting for approximately one quarter of all nosocomial infections, contribute to longer hospital stays and higher medical costs. Clinical failure of antibiotic treatment often is associated with increasing drug resistance.

Non-duplicated microbial isolates obtained at our institution from surgical patients were identified and tested for antimicrobial susceptibility using the Sceptor system in 2001-2002 and the Phoenix system in 2003-2005. Epidemiologic data were extracted using Epicenter and Powerlab. During selected periods, genetic and biochemical characterization was performed by pulsed-field gel electrophoresis, colony blot hybridization, gene amplification and sequencing, isoelectric focusing, and enzyme kinetics.

The specimens were most commonly isolated from infections at surgical sites (24.0%), the urinary tract (19.0%), and blood stream (10.6%). Isolates of Escherichia coli showed an increasing prevalence of resistance to penicillins, third-generation cephalosporins, ciprofloxacin, and gentamicin, whereas the prevalence of resistant Staphylococcus aureus generally declined. Highly aggressive multi-drug-resistant (MDR) Pseudomonas aeruginosa strains were widespread, although colistin remained effective in 100% of cases. A significant increase was seen in infections attributable to S. epidermidis and Candida albicans. The overall number of Enterobacteriaceae carrying extended-spectrum beta-lactamases increased continuously, and new resistance traits emerged. It appeared that the TEM-92 determinant moved from Enterobacteriaceae to nonfermenting gram-negative rods such as Acinetobacter baumannii.

The number and type of antimicrobial-resistance determinants are increasing.