Introduction. Biofilm formation is one of the main virulence factors in Pseudomonas aeruginosa infections. This study is aimed at investigating the presence of genes involved in biofilm formation in clinical P. aeruginosa isolates. Material and Methods. A cross‐sectional study was conducted on 112 P. aeruginosa isolates. The biofilm formation assay was performed on all isolates. Antimicrobial resistance was determined by the disk diffusion method, and the presence of genes was detected by polymerase chain reaction. Isolates were typed with Rep‐PCR. Results. The results of biofilm formation demonstrated that 85 strains (75.9%) were biofilm producers, and 27 strains (24.1%) were nonproducer isolates. Antibiotic susceptibility pattern in biofilm‐positive and biofilm‐negative isolates obtained from hospitalized patients showed a high rate of antibiotic resistance to amoxicillin with 95.7% and 92.3%, respectively. Based on PCR amplification results, the frequency of genes involved in biofilm formation among all isolates was as follows: algD (78.6%), pelF (70.5%), pslD (36.6%), Ppgl (0%), and PAPI-1 (77.6%). Rep‐PCR typing demonstrated that 112 P. aeruginosa isolates were classified into 57 types according to 70% cut‐off. The predominant type was A which contained 15 isolates. Moreover, 7 isolates were clustered in genotype B, followed by C type (6), D (4), E (4), F (4), G (4), H (3), I (3), J (3 isolates), and 12 genotypes, each containing two isolates. Also, 35 isolates were distributed in scattered patterns and showed single types. Conclusion. Study results showed significant association between biofilm formation and resistance to antibiotics such as ceftazidime and meropenem. Analysis of Rep‐PCR patterns indicated that the evaluated isolates were heterogeneous, relatively.

This study determined the mechanisms and patterns of antimicrobial resistance among the isolates obtained from different wards of a teaching hospital in the city of Mashhad in northeast-Iran. Between January 2012 and the end of June 2012, 36 isolates of Acinetobacter baumannii (A. baumannii) were collected from different wards of Ghaem Hospital. Antimicrobial susceptibility testing and epsilometer-testing (E-test) were performed. The genetic resistance determinants of A, B and D classes of β-lactamases, aminoglycoside modifying enzymes (AMEs), efflux pumps and ISAba1 elements were assessed by PCR. REP-PCR was performed to find the genetic relatedness of the isolates. Colistin was the most effective antibiotic of those tested, where all isolates were susceptible. E-test results revealed high rates of resistance to imipenem, ceftazidime and ciprofloxacin. The majority of isolates (97%) were multidrug-resistant (MDR). OXA-51, OXA-23 and tetB genes were detected in all isolates, but OXA-58, IMP and tetA were not detected. The prevalence of OXA-24, blaTEM, blaADC, blaVIM and adeB were 64%, 95%, 61%, 64%, and 86% respectively. ISAba1 were found to be inserted into the 5' end of OXA-23 in 35 isolates (97%). Of the AMEs, aadA1 (89%) were the most prevalent, followed by aphA1 (75%). The band patterns reproduced by REP-PCR showed that 34 out of 36 isolates belonged to one clone and two singletons were identified. The results confirmed that refractory A. baumannii isolates were widely distributed. It warned the hospital infection control team to exert strict measures to control the infection. An urgent surveillance system should be implemented.