Pak J Med Sci 2008 Vol. 24 No. 4 www.pjms.com.pk 537 Original Article CARBAPENEM RESISTANCE IN GRAM-NEGATIVE BACILLI ISOLATES IN AN IRANIAN 1000-BED TERTIARY HOSPITAL Mohammad Rahbar 1 , Mohammad Kabeh-Monnavar 2 , Kamal Khadem Vat an 3 , Asgar Fadaei -haqi 4 , Far shad Shaker i an 5 ABSTRACT Obj ect ive: Carbapenems are bet a-lact amase ant ibiot ics, present ly considered as most pot ent agent s f or t reat ment of inf ect ions caused by Gram-negat ive bacilli. The aim of t his st udy was t o det ermine resist ance of Pseudomonas aeruginosa, Acinet obact er baumannii and Kl ebsi el l a pneumonniae as prevalent nosocomial agent s t o commonly used ant ibiot ics including carbapenems such as imipenem and meropenem. Met hodology: A total of 202 gram-negative bacilli including K.pneumoniae, P aeruginosa and A.baumannii isolated from hospitalized patients in Milad hospital of Tehran were subj ect for suscept ibilit y t est ing. Suscept ibilit y t est ing was perf ormed by disk dif f usion and MIC met hods as recommended by Clinical Laborat ory St andards Inst it ut e (CLSI) Result s : All isolat es of K. pneumonia were suscept ible t o imipenem and meropenem. Resist ance in non-ferment ing gram-negat ive bacilli (NFGB) was prevalent . P . aer ugi nosa isolat es exhibit ed 7.5%and 40.2%resist ance t o imipenem and meropenem respect ively. The maj orit y isolat es of Aci net obact er baumanni i were mult i-drug resist ant and resist ance of t his organism t o imipenem and meropenem was 27.7%and 38. 5%respect ively. Conclusions: Our st udy revealed t hat in spit e of resist ance of K.pneumoniae t o commonly used ant ibiot ics, all isolat es were suscept ible t o imipenem and meropeem. More t han 80%isolat es of A .bammanni were resist ant t o commonly used ant ibiot ics. About 40.2%isolat es of P . aer ugi nosa and (38. 5%) isolat es of A.baumannii were resist ant t o meropenem respect ively. KEY WORDS: Carbapenem resist ance, Non-ferment er gram- negat ive bacilli. Pak J Med Sci July - September 2008 Vol. 24 No. 4 537-540 How t o cit e t his art icle: Rahbar M, Monnavar KM, Vatan KK, Fadaei-haq A, Shakerian F. Carbapenem resistance in gram-negative bacilli isolates in an Iranian 1000-bed Tertiary Hospital. Pak J Med Sci 2008; 24(4): 537-40. Correspondence Dr. Mohammad Rahbar, Department of Microbiology, Iranian Reference Healt h Laborat ories, Tehran, Iran. E-mail: mhhf_rz@yahoo.com * Received for Publicat ion: February 8, 2008 * Revision Received: February 21, 2008 * Revision Accepted: June 10, 2008 INTRODUCTION Carbapenems was first introduced in 1980 and are now frequently used as the last choice in treating serious infections caused by multidrug-resistant strains of gram negative bacilli. These antibiotics are stable to ß-lactamase including the extended spectrum ß -lactamase (ESBLs) and AmpC produced by gram –negative bacilli. 1-4 The carbapenems are a class of beta- lactamase antibiotics that differ from the peni- cillins by the substitution of a carbon atom for a sulfur atom and by the addition of a double bond to the five –membered ring of the peni- cillin nucleus. 5 Carbapenems bind bacterial