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Background: Extended-spectrum beta-lactamase (ESBLs) producing bacteria are issued as a serious problem considering their ability to hydrolyze most of beta-lactam antibiotics. The outbreak of infections derived by ESBL-producing enterobacteriaceae is increasing throughout the world. Therefore, this study aims to determine a pattern of antibiotic resistance and investigate the extended-spectrum beta-lactamases production of enterobacteriaceae isolates separated from clinical specimens.Materials and Methods: In this study, 170 various strains of enterobacteriaceae isolated from clinical specimens in teaching hospitals of Arak cultured and identified applying standard methods during one year (2010-2011). The antibiotic resistance of isolates was investigated through disk Agar diffusion according to CLSI criteria. The resistant isolates against ceftazidime and cefotaxime antibiotics were studied through the combined disk test for the final confirmation of ESBL-production. The minimum inhibitory concentration was determined through micro broth dilution.Results: In this study, the resistance rate of various strains of enterobacteriaceae against amoxiclav, cefotaxime, ceftriaxone, ceftazidime, cefoxitin, cefotetan, meropenem and imipenem were respectively, 91.1%, 70%, 68.8%, 62.9%, 28.2%, 11.1%, 11.1% and 1.7%. Among 125 resistant enterobacteriaceae isolates against ceftazidime or cefotaxime, 108 isolates (86.4%) had ESBL-positive phenotype and 17 isolates (13.6%) had ESBL-negative phenotype. The MICs of the resistant isolates were indicated within a range of 16 to 512 µg/ml for ceftazidime and 64 to 512 µg/ml for cefotaxime.Conclusion: According to the results of this study, imipenem is the most effective antimicrobial antibiotic. On the other hand, the present study indicates that the bacteria within the family of ESBL producing enterobacteriaceae are highly prevalent among the patients. The increase in rate of such cases is often resulted by irrational antibiotic prescription. Application of new antimicrobials, limitation of the use of antimicrobial factors and increasing the utilization of infection control tools are all required in order to solve this problem.

Mycobacterium tuberculosis growth rate is closely coupled to rRNA transcription which is regulated through carD gene. The aim of this study was to determine the sequence of carD gene in drug susceptible and resistant clinical isolates of M. tuberculosis and designing of a PCR assay based on carD sequence for rapid detection of this bacterium.Specific primers for amplification of carD gene were carefully designed, so that whole sequence of gene could be amplified; therefore primers were positioned at the upstream (promoter of this gene and ispD gene) and downstream (in ispD gene). DNA from 41 clinical isolates of M. tuberculosis with different pattern of drug resistance was used in the study. PCR conditions and annealing temperature were designed by means of online programs. PCR products were sequenced by ABI system.PCR product of carD gene was a 524 bp fragment. This method could detect all resistant and susceptible strains of M. tuberculosis. The size of amplified fragment was similar in all investigated samples. Sequence analysis showed that there was similar sequence in all of our isolates therefore probably this gene is considered to be conservative. Translation of nucleotide mode to amino acids was showed that TRCF domain in N-terminal of protein CarD was found to be fully conservative.This is the first study on the sequence of carD gene in clinical isolates of M. tuberculosis. This conservative gene is recommended for use as a target for designing of suitable inhibitors as anti-tuberculosis drug because its importance for life of MTB. In the other hand, a PCR detection method based on detection of carD gene was recommended for rapid detection in routine test.