Epidemiology of Gram-negative antibiotic resistance in outpatients: a year of surveillance

Enterobacteriaceae are etiologic agents of nosocomial and community acquired infections such as urinary tract infections, intra-abdominal infections and bacteremia and may also cause upper and lower respiratory tract or skin and soft tissue infections. The most frequent species causing community-acquired infections are Escherichia coli, Klebsilella pneumoniae and Proteus mirabilis with other species, such as Enterobacter spp., Serratia marcescens and Citrobacter spp. mainly encountered in hospital acquired infections. Pseudomonas aeruginosa is the cause of 10-15% of nosocomial infections. These micro-organisms have developed extended spectrum beta-lactamases (ESBL), causing resistance to ceftazidime, ceftriaxone, cefotaxime and aztreonam. Our hospital, a large northern Italian teaching hospital with 600 beds, performs similar to 170 000 microbiological tests per year, which are used to follow trends in antimicrobial resistance of micro-organisms causing nosocomial and community acquired infections. Gram-negative strains were isolated and identified according to standard laboratory procedures.