Antimicrobial Resistance Patterns And Correlation Between Biofilm Formation And Class 1 Integrons In Escherichia Coli Isolates From Tongliao,north-east China

Background and ObjectiveEscherichia coli, an important member of microbial flora of intestinal tract, may become an opportunistic pathogen responsible for extra-intestinal infections, including urinary tract infections, bacteremia, and meningitis. According to the 2014 global surveillance report of antimicrobial resistance, the prevalence of both third generation cephalosporin and fluoroquinolone resistance in E. coli isolates has remarkably increased among 114 countries worldwide. Therefore, to investigate the current status of drug resistance of E. coli is necessary for optimizing the use of antibiotics and providing the guidance for antimicrobial therapy. Bacterial biofilms—sessile microbial communities formed on solid surfaces—are made up of a polysaccharide matrix that contains peptidoglycan, fibrin and phospolipid, etc. Bacterial biofilms have attracted extensive research because of biofilm-associated phenotypes such as high resistance to antibiotics. Class I integron, the most frequently found in clinical isolates of Gram-negative bacteria, can capture extra-cellular resistance gene and integrate resistance gene cassettes by site-specific recombination. On the other hands, many resistance genes present as gene cassettes in an integron leading to the development of multi-drug resistance. Our aim was to investigate the changes in the patterns of antimicrobial resistance and the integron carriage of E. coli isolates in Tongliao and to study the expression of class I integrase in both biofilm-enclosed bacteria and planktonic bacteria. Materials and Methods:A total of 99 E. coli clinical isolates, collected at Tongliao hospital between October 2013 and March 2014, were examined in this study. The antimicrobial susceptibility of clinical isolates was determined using disk diffusion approach. Microtitre plate assays were performed to examine the biofilm formation of E. coli isolates. Class I integron carriage of 99 E. coli isolates was detected by PCR assay. The gene cassette regions for the class I integron were amplified using primer pairs, RT-PCR was employed to detect the expression of Class I integron in both biofilm-enclosed bacteria and planktonic bacteria. Results and Conclusion:Antimicrobial susceptibility testing revealed that more than 50(>50%) of the isolates were resistant to 13 of 23 antibiotics tested in this study. Among 99 clinical isolates, low frequencies of resistance were found to imipenem(7% of isolates) and meropenem(5% of isolates). The capacity of 99 E. coli clinical isolates to form biofilm was tested using microtitre plate assays. Most of the strains tested formed biofilm after 24 hours. The biofilm production is closely related to the resistance of isolates to amikacin, piperacillin/tazobactam, and aztreonam. PCR and DNA sequencing analysis revealed the presence of class I integrons in 55 isolates(55.6%), and gene cassettes of class I integrons in 36 isolates(36.4%). The class I integron carried two types of gene cassettes. One cassette array in 3 isolates was dfr A17 and aad A5, the other in one isolate was aar-3 and dfr A27. Quantitative Real-time PCR assay demonstrated that the expression level of class I integrase gene exhibited more significantly increased in biofilm-enclosed strains than in planktonic strains.