Changes in gram negative microorganisms’ resistance pattern during 4？years period in a referral teaching hospital; a surveillance study

During a four-year period (2007–2010) isolates derived from all patients admitted to infectious diseases ward of Imam Khomeini Hospital, the major referral center for infectious disease in Iran with the highest admission rates, were evaluated. Based on disk diffusion method and zone of inhibition size, the microorganism was regarded as to be sensitive, resistant or has intermediate susceptibility to the antimicrobial agents.The widest spread Gram-negative microorganism in all of isolates taken together in our study was E.coli (30%) followed by Stenotrophomonas maltophilia in 28.6% and Enterobacter spp. in 11.9%, respectively. The susceptibility to amikacin, imipenem, piperacillin/tazobactam, and nitrofurantoin was equal or above 50% for all microorganisms over four years. However, the susceptibility to ampicillin, ampicillin/sulbactam, cefotaxim, and ceftriaxone was less than 50% in derived isolates during the study period.In conclusion, the finding of the present study revealed that resistance rate to common antimicrobial agents in Iran is growing and isolates were susceptible mostly to broad-spectrum antibiotics including imipenem and piperacillin/tazobactam.Antibiotic resistance is a critical challenge for infective diseases management around the word [1-3]. Infection with a resistant strain has been associated to higher rate of morbidity and mortality as well as prolonged length of hospital and intensive care unit stay and increased expenses for the healthcare systems [3,4].Surveillance studies evaluating antimicrobial susceptibilities are of great value in providing information for prescribing the most appropriate agent [5]. These studies could be used as a guide in antimicrobial usage policies in order to halt the expansion of microorganism resistance [6-10].Although there are few reports on the antibiotic resistance in Iran, many of them are simple point-in-time prevalence studies or evaluated pathogens involved in a specific infectious disease [11-14]. Prese