Detection of Genes Related to Linezolid Resistance (poxtA, cfr, and optrA) in Clinical Isolates of Enterococcus spp. from Humans: A First Report from Iran.

Background: Enterococci may develop resistance to linezolid through chromosomal mutations that involve specific linezolid resistance genes, such as cfr, optrA, and poxtA. The objective of this study was to evaluate the antibiotic susceptibility of enterococcal isolates and identify cfr, optrA, and poxtA genes in MDR isolates. Materials and Methods: Enterococcal isolates were collected from various clinical specimens at Al-Zahra, Amin, and Khorshid Hospitals in Isfahan. The Enterococcus isolates were identified as belonging to the E. faecalis and E. faecium species by using specific gene (D alanine D alanine ligase ddl) sets in PCR. To detect cfr, optrA, and poxtA genes among the species, a multiplex-PCR assay was performed. Results: Out of 175 isolates, E. faecalis predominated 129/175 (73.7%). Furthermore, the prevalence of vancomycin-resistant Enterococci (VRE) and linezolid-resistant Enterococci (LRE) was 29.7% and 4%, respectively. The overall prevalence of MDR was 91.1%, 68.9%, and 66.6% of E. faecium, E. faecalis, and other Enterococcus spp., respectively. Interestingly, the frequency of optrA (71.4%) in E. faecium and poxtA and crf (42.8%) in E. faecalis were detected among LRE species. A statistically significant relationship (P < 0.05) was found between the presence of the three genes and the occurrence of LRE. Conclusion: This is the first study to report the detection of linezolid resistance genes (cfr, optrA, and poxtA) in clinical Enterococcus spp. isolates from Iran, conducted at Isfahan University of Medical Sciences hospitals. The emergence of enterococcal strains that resist linezolid is concerning as it can lead to the spread of resistant strains among patients, resulting in treatment failure.

Evolutionary trajectories of beta-lactamase NDM and DLST cluster in Pseudomonas aeruginosa: finding the putative ancestor.

Pseudomonas aeruginosa has different antibiotic resistance pathways, such as broad-spectrum lactamases and metallo-ß-lactamases (MBL), penicillin-binding protein (PBP) alteration, and active efflux pumps. Polymerase chain reaction (PCR) and sequencing methods were applied for double-locus sequence typing (DLST) and New Delhi metallo-ß-lactamase (NDM) typing. We deduced the evolutionary pathways for DLST and NDM genes of P. aeruginosa using phylogenetic network. Among the analyzed isolates, 62.50% of the P. aeruginosa isolates were phenotypically carbapenem resistance (CARBR) isolates. Characterization of isolates revealed that the prevalence of blaNDM, blaVIM, blaIMP, undetermined carbapenemase, and MexAB-OprM were 27.5%, 2%, 2.5%, 12.5%, and 15%, respectively. The three largest clusters found were DLST t20-105, DLST t32-39, and DLST t32-52. The network phylogenic tree revealed that DLST t26-46 was a hypothetical ancestor for other DLSTs, and NDM-1 was as a hypothetical ancestor for NDMs. The combination of the NDM and DLST phylogenic trees revealed that DLST t32-39 and DLST tN2-N3 with NDM-4 potentially derived from DLST t26-46 along with NDM-1. Similarly, DLST t5-91 with NDM-5 diversified from DLST tN2-N3 with NDM-4. This is the first study in which DLST and NDM evolutionary routes were performed to investigate the origin of P. aeruginosa isolates. Our study showed that the utilization of medical equipment common to two centers, staff members common to two centers, limitations in treatment options, and prescription of unnecessary high levels of meropenem are the main agents that generate new types of resistant bacteria and spread resistance among hospitals.

In vitro antimicrobial effects of green tea, microwaving, cold boiled water, and chlorhexidine on Streptococcus mutans and Candida albicans on silicone pacifiers.

Background: This study aimed to compare the antimicrobial effects of green tea, microwaving, cold boiled water, and chlorhexidine (CHX) on Streptococcus mutans and Candida albicans on silicone pacifiers. Materials and Methods: In this in vitro experimental study, 60 equal-size samples of silicone pacifiers were cut, ultraviolet sterilized, and randomly divided into two groups (n = 30) for immersion in 0.5 McFarland standard suspension of S. mutans and C. albicans. The samples in each group were then randomly divided into five subgroups (n = 6) for disinfection with 0.12% CHX, cold boiled water, green tea, microwaving for 7 min, and distilled water. The sample suspensions were cultured on blood agar (for S. mutans) and Sabouraud dextrose agar (for C. albicans) and incubated. The number of colonies was counted after 24 and 48 h. Data were analyzed using the Kruskal-Wallis and Mann-Whitney tests (P < 0.05). Results: At 24 and 48 h, the S. mutans colony count was the lowest in CHX and green tea subgroups followed by microwave, cold boiled water, and distilled water subgroups (P < 0.05). Conclusion: CHX and green tea can significantly decrease the S. mutans and C. albicans colony count on silicone pacifiers.

Comparative Evaluation of Antibacterial Effect of Propolis and Aloe Vera, Xylitol, and Cpp-Acp Gels on Streptococcus mutans and Lactobacillus in Vitro.

INTRODUCTION: Early childhood caries is a kind of caries occurring in deciduous teeth. Bacteria are among the main factors. Antibacterial agents such as fluoride are used in both prevention and treatment, but their application in children faces limitations such as fluorosis. Therefore, novel methods of caries prevention among the children are mainly focused on the use of fluoride-free active ingredients. In this comparative study, antibacterial effects of gels containing propolis and aloe vera, fluoride, xylitol, and CPP-ACP were investigated. METHODS: This is an in vitro study. By plate well technique, plates containing gels were created in the culture medium of Streptococcus mutans and Lactobacillus, and their antibacterial impacts were evaluated by measuring the inhibition zone after 24, 48, and 72 hours. Then, different concentrations of each gel were evaluated in the same way for the antibacterial properties. For each sample, this process was iterated 3 times, where the average was declared as the final number. The collected data were entered in SPSS 24. RESULTS: In both bacteria, propolis gel and aloe vera had the highest zone of inhibition, followed by fluoride and xylitol in the second and third places, respectively. Different concentrations of gels are significantly different in terms of antimicrobial effect (P value ≤ 0/05). The antimicrobial effect of propolis and aloe vera gel was kept up to the concentration of 1/16. As the bacterial and gel contact time is prolonged, the antibacterial effect of different gels increases, but the difference is not statistically significant (P value = 0.109). CPP-ACP gel had no antimicrobial effect at any concentration. CONCLUSION: Propolis and aloe vera gel had a greater antimicrobial effect than other gels, where such effect was observed in low concentrations. CPP-ACP gel had no antimicrobial properties.

Discovery of potential inhibitors against New Delhi metallo-ß-lactamase-1 from natural compounds: in silico-based methods.

New Delhi metallo-ß-lactamase variants and different types of metallo-ß-lactamases have attracted enormous consideration for hydrolyzing almost all ß-lactam antibiotics, which leads to multi drug resistance bacteria. Metallo-ß-lactamases genes have disseminated in hospitals and all parts of the world and became a public health concern. There is no inhibitor for New Delhi metallo-ß-lactamase-1 and other metallo-ß-lactamases classes, so metallo-ß-lactamases inhibitor drugs became an urgent need. In this study, multi-steps virtual screening was done over the NPASS database with 35,032 natural compounds. At first Captopril was extracted from 4EXS PDB code and use as a template for the first structural screening and 500 compounds obtained as hit compounds by molecular docking. Then the best ligand, i.e. NPC120633 was used as templet and 800 similar compounds were obtained. As a final point, ten compounds i.e. NPC171932, NPC100251, NPC18185, NPC98583, NPC112380, NPC471403, NPC471404, NPC472454, NPC473010 and NPC300657 had proper docking scores, and a 50 ns molecular dynamics simulation was performed for calculation binding free energy of each compound with New Delhi metallo-ß-lactamase. Protein sequence alignment, 3D conformational alignment, pharmacophore modeling on all New Delhi metallo-ß-lactamase variants and all types of metallo-ß-lactamases were done. Quantum chemical perspective based on the fragment molecular orbital (FMO) method was performed to discover conserved and crucial residues in the catalytic activity of metallo-ß-lactamases. These residues had similar 3D coordinates of spatial location in the 3D conformational alignment. So it is posibble that all types of metallo-ß-lactamases can inhibit by these ten compounds. Therefore, these compounds were proper to mostly inhibit all metallo-ß-lactamases in experimental studies.

Investigation of carbapenem resistant Acinetobacter baumannii ST2 in Iran.

This study investigated carbapenem resistance among Acinetobacter baumannii isolated from respiratory specimens. Epidemiological relationship of the isolates was also evaluated. In this study, 81 respiratory specimens of A. baumannii from AL Zahra Hospital were confirmed by phenotypic and genotypic methods. Antimicrobial susceptibility was performed by disc diffusion method. Carbapenem resistance genes were identified by PCR. The isolates were typed by RAPD-PCR and multilocus sequence typing (MLST) methods. All isolates were resistant to imipenem and 80 isolates to meropenem. Frequency of oxacillinase genes was as follows: blaOXA-23 gene was positive in 74 (91.3%), blaOXA-24 gene in 50 (61.7%) and blaOXA-58 was not found in any isolates. On the other hand 22 (27.2%) isolates contained blaIMP-1, 3 (3.7%) isolates contained blaIMP-2 gene, 5 (6.2%) isolates contained blaVIM-1, 4 (5%) isolates had blaVIM-2 and none of the isolates had blaSIM-1 gene. RAPD-PCR typing identified 16 different patterns, with one pattern being the most frequent one in 26 isolates. In MLST 6 different sequence types were identified, the most predominant being ST2 belonging to clonal complex 2. The results of this study showed high resistance to carbapenems as well as high abundance of oxacillinase genes.

The Occurrence of Type I, II, and III Integrons in Multi-drug Resistance and Methicillin-Resistant Staphylococcus aureus Isolates in Iran.

Integrons are mobilizable platforms-DNA elements with impacts on moving antibiotic resistance genes among bacteria and capable of spreading multi-drug resistance (MDR) in pathogens. Methicillin-resistant Staphylococcus aureus (MRSA) strains are the main cause of community-acquired and nosocomial infections with high mortality and morbidity rates worldwide. This work is mainly aimed at calculating the frequency of Type I, II, and III integrons within multi-drug resistance and Methicillin-resistant S. aureus Isolates in Iran. In this cross-sectional study, 230 clinical isolates of S. aureus were gathered from patients of educational hospitals in the provinces of Iran. These isolates were verified utilizing particular biochemical examinations and then assessed for antibiotic susceptibility through disk diffusion technique and standard procedures were done. Genomic and plasmid DNA of all isolates were extracted using Extraction Kit and PCR assay was used for the detection of Type I, II and III integrons genes. Out of the 230 S. aureus isolates, 136 (59.1%) isolates were MRSA and 141 (61.3%) isolates exhibited the MDR pattern. PCR and sequencing showed that 57 (24.8%) of tested isolates carry Type I integron. Among the isolates investigated, MRSA and MDR isolates showed frequencies of 56.1% and 57.9%, respectively. Type II and III integrons were found in none of 230 isolates. The IntI I gene was present in approximately one-quarter of this study isolates. The great prevalence rate of MDR and MRSA isolates and concurrently the existence of Type I integron among those isolates have been considered an important concern in medical society.

Correction to: Investigation of antimicrobial susceptibility, class I and II integrons among Pseudomonas aeruginosa isolates from hospitalized patients in Isfahan, Iran.

Following publication of the original article [1], an error was reported in the tables due to a typesetting mistake. Table 3 is presented as a duplicate of Table 2. In this Correction, the correct presentation of Table 3 is shown.

Investigation of antimicrobial susceptibility, class I and II integrons among Pseudomonas aeruginosa isolates from hospitalized patients in Isfahan, Iran.

OBJECTIVES: The role of integrons in the transfer of antibiotic resistance is one of the important issues, therefore, this study is aimed to investigate antibiotic resistance pattern and prevalence of class 1 and 2 integrons in P. aeruginosa isolated. RESULTS: Out of 72 confirmed P. aeruginosa isolates, 50% were from ICU patients. Antibacterial susceptibility pattern showed that isolates were most resistant to ceftazidime (76.4%) and colistin was the most effective antibiotic (100%) and molecular analysis of class I and II integrons showed 55.5% and 29.1% of isolates were positive, respectively and the proportions of MDR isolates were significantly higher among integron-positive isolates with 73.6% compared to negative isolates with 22.9%. Our results showed that there was a correlation among class 1 and 2 integrons with MDR P. aeruginosa isolates. According to the importance of integrons in acquisition and dissemination of antibiotics resistance genes, the performance of antibiotic surveillance programs and investigating the role of integrons is recommended to control the spreading of antibiotics resistance genes.

First Report of the Isolation of Nocardia thailandica from the Bronchoalveolar Lavage of a Patient in Iran.

Nocardiae are Gram-positive, filamentous, aerobic, relatively slow-growing, and weakly acid-fast bacteria which cause nocardiosis in humans. We describe a 53-year-old patient with chronic bronchitis referred to Al-Zahra Hospital, Isfahan. A bronchial washing sample was taken from the patient. A Nocardia-like microorganism was detected in microscopic evaluation. Based on the phenotypic and 16S rRNA gene sequencing, the isolate was identified as Nocardia thailandica. The patient was treated with trimethoprim-sulfamethoxazole and linezolid. This is the first report of the isolation of Nocardia thailandica from Iran.

High rate of carbapenem-resistant Klebsiella pneumoniae detected from hospital equipments in Iran.

The objective of this study was to assess the prevalence, antibiogram, and related genes of carbapenem-resistant Klebsiella pneumoniae (CRKP) among hospital environment samples. A total of 250 samples were taken from different surfaces and medical devices of three hospitals in Isfahan, Iran. All samples were cultured and K. pneumoniae strains were identified by conventional microbiological methods and polymerase chain reaction (PCR). Antibiogram of isolates was performed by disk diffusion method and production of carbapenemases and metallo-ß-lactamases (MBLs) was confirmed using modified Hodge test and E-test, respectively. Molecular detection of the related genes was carried out by PCR. Overall, 37 (14.8%) K. pneumoniae strains were isolated, of which 34 (91.9%) strains were resistant to carbapenems. Twenty-eight (82.4%) isolates were positive for carbapenemases and seven (20.6%) isolates were phenotypically MBL producers. The results of PCR showed that the prevalence of blaOXA-48, blaNDM, blaIMP, blaSHV, blaCTX-M, blaTEM, and class 1 integron among CRKP isolates was 70.6%, 52.9%, 2.9%, 100%, 82.4%, 55.9%, and 76.5%, respectively. However, blaKPC, blaGES, blaIMI, blaVIM, and class 2 integron were not detected in any of the isolates. This study showed that the environment of our hospitals is contaminated with CRKP and it emphasizes the importance of using standard methods for infection control.

The emergence of blaOXA-48 and blaNDM among ESBL-producing Klebsiella pneumoniae in clinical isolates of a tertiary hospital in Iran.

The aim of this study was to investigate the prevalence of carbapenem-resistant Klebsiella pneumoniae (CRKP) and the most common types of carbapenemases, metallo-beta-lactamases (MBLs), and extended-spectrum beta-lactamases (ESBLs) among CRKP isolates in a tertiary hospital in Isfahan, Iran. Eighty non-repetitive clinical isolates of K. pneumoniae were obtained from different clinical specimens. Antibiotic resistance pattern of isolates was determined by disk diffusion method and production of carbapenemases and MBLs was confirmed using modified Hodge test and E-test, respectively. Molecular detection of the antibiotic resistance genes was performed using PCR. Fifty-one (63.8%) isolates have decreased susceptibility to carbapenems, of which 46 (90.2%) isolates were as carbapenemase producer and four (7.8%) isolates were positive for MBLs, phenotypically. The results of PCR showed that the prevalence of blaOXA-48, blaNDM, blaSHV, blaCTX-M, and blaTEM genes among CRKP isolates were 90.2%, 15.7%, 98%, 96.1%, and 90.2%, respectively. No isolates carrying the blaKPC, blaGES, blaIMI, blaVIM, and blaIMP genes were detected. This study showed that the production of OXA-48 is one of the main mechanisms of resistance to carbapenems in CRKP isolates in Isfahan. In addition, the dissemination of NDM-producing CRKP isolates is a potential risk for the health care system of this area in the near future.

Determination of antibiotic resistance pattern and prevalence of OXA-type carbapenemases among Acinetobacter baumannii clinical isolates from inpatients in Isfahan, central Iran.

Acinetobacter baumannii is one of the most important bacterial species with the ability to produce OXA-type carbapenemases. We aimed to evaluate the prevalence of OXA-type carbapenemases among clinical isolates of A. baumannii in three major hospitals of Isfahan. In this cross-sectional descriptive study, 153 non-repeated strains of A. baumannii were isolated from various clinical samples of hospitalized patients in Al-Zahra, Imam Mousa Kazem, and Shariati hospitals from October 2015 to October 2016. Antimicrobial susceptibility testing for imipenem, meropenem, ertapenem, cefepime, ceftazidime, ceftriaxone, piperacillin-tazobactam, gentamicin, amikacin, ciprofloxacin, and tetracycline was performed using the disk diffusion method. In order to identify bla-oxa genes, a multiplex polymerase chain reaction was used. The resistance rates in A. baumannii isolates to beta-lactam antibiotics including imipenem, ertapenem, meropenem, cefepime, ceftazidime, ceftriaxone, and piperacillin/tazobactam were 100%, 100%, 99.3%, 97.4%, 96.7%, 97.4%, and 98.6%, respectively. PCR assay showed the presence of bla-oxa genes in all isolates. The bla-oxa-51 gene was recognized in all (100%) isolates, 90.8% and 62.1% of isolates possessed the bla-oxa-23 and bla-oxa-24 genes, respectively, while the bla-oxa-58 gene was not detected in any of the isolates. Also, 56.2% of isolates had both the bla-oxa-23 and bla-oxa-24 genes simultaneously. We found that the prevalence of OXA-type carbapenemases among carbapenem-resistant A. baumannii isolates is high in Isfahan, with OXA-23 being the major carbapenemase mechanism responsible for the resistance phenotype.

Investigation of Class I, II, and III Integrons Among Acinetobacter Baumannii Isolates from Hospitalized Patients in Isfahan, Iran.

OBJECTIVES: This study aimed to determine the prevalence of class I, II, and III integrons among clinical Acinetobacter baumannii isolates collected from hospitalized patients. METHODS: This cross-sectional study was conducted at two teaching hospitals in Isfahan, Iran, from October 2015 to October 2016. A total of 147 non-duplicate A. baumannii isolates were collected from clinical specimens and identified as A. baumannii using standard microbiological methods and confirmed by genotyping. Antimicrobial susceptibility was determined using disc diffusion method, and the presence of integron genes was performed using the polymerase chain reaction. RESULTS: Out of 147 confirmed A. baumannii isolates, 97.3% of isolates were extensive drug-resistant (XDR) and 2.7% were multidrug-resistant (MDR). Class I and II integrons were detected in 63.9% and 78.2% of the A. baumannii, respectively. Class III integron was not detected in any of the isolates. CONCLUSION: Our results show a high prevalence of classes I and II integrons which may play a key role in the acquisition of MDR and XDR phenotype among A. baumannii isolates in our region. Therefore, use of appropriate infection control in clinical settings and implementation of treatment strategies is necessary for our hospitals.

Prevalence of CTX-M and TEM ß-lactamases in Klebsiella pneumoniae Isolates from Patients with Urinary Tract Infection, Al-Zahra Hospital, Isfahan, Iran.

BACKGROUND: Extended-spectrum ß-lactamase (ESBL)-producing is a significant resistant mechanism to ß-lactams in Enterobacteriaceae, especially in Klebsiella pneumoniae. The main objectives of this study were to genetically characterize urinary clinical isolates of K. pneumoniae through the investigating of blaTEM, blaCTX-M and using molecular typing by Enterobacterial repetitive intergenic consensus polymerase chain reaction (ERIC-PCR) method. We also determined the frequency of antibiotic resistance of K. pneumoniae strains to characterize the ß-lactamases included. MATERIALS AND METHODS: A cross-sectional study was carried out to evaluate 98 strains of K. pneumoniae isolated from urine culture of outpatients referred to Al-Zahra Hospital, Isfahan, Iran. Antibiotic susceptibility testing was performed using Kirby-Bauer's method. Screening of ESBLs was carried out using double-disk screening test. PCR technique was performed to detect TEM and CTX-M genes. The total DNA of each strain was tested by ERIC-PCR. RESULTS: In 98 K. pneumoniae studied clinical isolates, 25.5% were ESBL producing and 44.9% multidrug-resistant (MDR). From 25 ESBL isolates, 23 (92%) cases showed MDR phenotype. In ESBL producing isolates, 23 (92%) were blaCTX-M and 19 (76%) blaTEM positive. The antimicrobial drug susceptibilities of ESBL isolates indicated high resistant rates for cefotaxime and ceftazidime. All 25 ESBL producing isolates were resistant to cefotaxime. Complex patterns of fingerprints isolates showed that 36% of the isolates were belonged to the cluster no 5. CONCLUSION: This study revealed high antimicrobial resistance rates among ESBL isolates which can lead to various health difficulties. Epidemiological data collection from patients is recommended to develop the strategies to manage antibiotic resistance.

High prevalence of multidrug-resistance uropathogenic Escherichia coli strains, Isfahan, Iran.

BACKGROUND AND OBJECTIVES: Urinary tract infection (UTI) is one of the most frequent infectious diseases and can occur in all age groups. Escherichia coli is the main cause of this infection. Multiple resistances to antimicrobial agents are increasing quickly in E. coli isolates and may complicate therapeutic strategies for UTI. The aim of this study was to determine the antibiotic resistance pattern and the multidrug-resistance (MDR) phenotypes in uropathogenic E. coli (UPEC). MATERIALS AND METHODS: A total of 135 UPEC isolates were collected from both outpatients (91 isolates) and inpatients (44 isolates) between September, 2012 and February, 2013. In order to determine the MDR among UPEC isolates, we have tested 15 antimicrobial agents and antibiotic susceptibility was done by Kirby-Bauer disk diffusion method. RESULTS: The percentage of MDR isolates (resistant to at least three drug classes such as aminoglycosides, fluoroquinolones, penicillins, cephalosporins, or carbapenems) was 68% in the inpatients and 61% in the outpatients. Antibiotic resistance to ampicillin, ceftazidim, nalidixic acid, and trimethoprim/sulfamethoxazole were higher than 50%. Amikacin, nitrofurantoin, and gentamicin showed markedly greater activity (89.1%, 85.9%, and 82.4% sensitivity, respectively) than other antimicrobial agents. Resistance to meropenem did show either in outpatients or in inpatients. INTERPRETATION AND CONCLUSIONS: The high prevalence of drug resistance among UTI patients calls for continuous monitoring of the incidence of drug resistance for appropriate empiric selection of antibiotic therapy. Empirical treatment of UTIs should be relied on susceptibility patterns from local studies.

Study on Prevalence, Antibiotic Susceptibility, and tuf Gene Sequence-Based Genotyping of Species-Level of Coagulase-Negative Staphylococcus Isolated From Keratitis Caused by Using Soft Contact Lenses.

OBJECTIVE: To study on antibiotic susceptibility and identify coagulase-negative Staphylococcus (CoNS) species based on tuf gene sequencing from keratitis followed by using soft contact lenses in Isfahan, Iran, 2013. METHODS: This study examined 77 keratitis cases. The samples were cultured and the isolation of CoNS was done by phenotypic tests, and in vitro sensitivity testing was done by Kirby-Bauer disk diffusion susceptibility method. RESULTS: Thirty-eight of isolates were conveniently identified as CoNS. In this study, 27 (71.1%), 21 (55.3%), and 16 (42.1%) were resistant to penicillin, erythromycin, and tetracycline, respectively. One hundred percent of isolates were sensitive to gentamicin, and 36 (94.7%) and 33 (86.8%) of isolates were sensitive to chloramphenicol and ciprofloxacin, respectively. Also, resistances to cefoxitin were 7 (18.4%). Analysis of tuf gene proved to be discriminative and sensitive in which all the isolates were identified with 99.0% similarity to reference strains, and Staphylococcus epidermidis had the highest prevalence among other species. CONCLUSIONS: Results of this study showed that CoNS are the most common agents causing contact lens-associated microbial keratitis, and the tuf gene sequencing analysis is a reliable method for distinguishing CoNS species. Also gentamycin, chloramphenicol, and ciprofloxacin are more effective than the other antibacterial agents against these types of bacteria.

Antibiotic Resistance Patterns and Genetic Diversity in Clinical Isolates of Pseudomonas aeruginosa Isolated From Patients of a Referral Hospital, Isfahan, Iran.

BACKGROUND: Pseudomonas aeruginosa is a well-known opportunistic pathogen, which affects hospitalized patients in different wards due to its natural resistance to drugs. OBJECTIVES: The purpose of the current study was to determine the antibiotic susceptibility profiles and genetic relatedness in P. aeruginosa isolated from patients admitted to a referral hospital in Isfahan, Iran. MATERIALS AND METHODS: Out of 150 analyzed samples, 54 P. aeruginosa isolates were recovered and were subjected to antibiotic resistance patterns and genetic diversity determination by Kirby-Bauer's disk diffusion method and RAPD-PCR, respectively. RESULTS: The highest percentage of resistance was observed against ceftazidime and imipenem with 30 (55.6%) isolates; meanwhile all isolates were sensitive to polymyxin B. Twenty-eight (51.8%) isolates revealed resistance to all applied antibiotics. RAPD-PCR (Random Amplified Polymorphic DNA- Polymerase Chain Reaction) results showed 54 unique genotypes, which were divided into 39 clusters. CONCLUSIONS: Although different source of P. aeruginosa may involve in patient colonization, genetically related strains were isolated from different wards and or the same ward of the hospital. Our results pointed to the restriction of currently used antibiotics in studied hospital. We hope that our results cast light on the control and transmission of the infection in the investigated hospital.