Background Blood infection is one of the major causes of morbidity and mortality among the newborns especially in developing countries, at the other hand being informed about antimicrobial resistance pattern for correct treatment is necessary. So the aim is study the bacterial agent in blood infection in newborns who were admitted in NICU of Imam Hussein hospital of Tehran and survey their antibiotic resistance pattern.

Methods In this study, microorganisms of blood samples of hospitalised infant in NICU from Imam Hussein, hospital of Tehran during one year isolated, and their antimicrobial resistance pattern was studied by Kirby-Bauer test.

Results During a year study on 105 blood samples, 81(77.1%) were gram negative and 24(22.9%) were gram positive organisms. Klebsiella pneumonia (30.5%), Entrobacter cloacae(21%) and Staphylococcus epidermidis(11.4%) were the most common gram negative and positive isolated microorganisms, respectively.

Early and Late onset septicemia in this study occurred with coagulase negative staphylococci and Klebsiella penumoniae. The most antimicrobial susceptibility in gram negative microorganisms were shown to Moxyfloxacin (88.1%) and Ciprofloxacin (84.2%) and in gram positive were shown to Vancomycin (83.3%). All the gram positive microorganisms were resistance (100%) to penicillin.

Conclusion This result shown that the most contamination in NICU is from gram negative bacteria.