en Life Science Life Science مقاله پژوهشی Original Research Article <span style="font-size:10pt"><span new="" roman="" style="font-family:" times=""><b><span style="font-size:9.0pt"><span style="background:#2d7f8f"><span style="color:white">Background & Objective:</span></span></span></b><b> </b><span style="font-size:9.0pt">Extended-spectrum beta-lactamases (ESBLs) are enzymes in bacteria that resist many antibiotics. Detection of <a name="_Hlk165045335">ESBLs</a> production is important as it&#39;s a marker of colonization and potential transfer to other patients. </span><span style="font-size:9.0pt">We studied the antibiotic susceptibility, biofilm formation capacity, and prevalence of ESBLs of opportunistic bacteria including <i>K. pneumoniae </i>and<i> E. coli</i>. The isolates capable of biofilm formation were analyzed among 100 <i>E. coli and</i> 104 <i>K. pneumoniae</i> isolates.</span><b> </b><span style="font-size:9.0pt"><span style="color:black"></span></span></span></span><br> <b><span style="font-size:9.0pt"><span style="background:#2d7f8f"><span style="color:white"><span style="letter-spacing:-.1pt">&nbsp;Materials & Methods:</span></span></span></span></b> <span style="font-size:9.0pt">This<b> </b>process involved collecting and identifying bacterial samples, testing antibiotic susceptibility, detecting <a name="_Hlk165045433">ESBLs</a> phenotypes, and multidrug-resistance (MDR) isolates, assessing biofilm formation capability, and evaluating results through statistical analysis.<span style="color:red"></span></span><br> <span style="font-size:10pt"><span new="" roman="" style="font-family:" times="">&nbsp;<span style="font-size:9.0pt"><span style="color:black"><span style="letter-spacing:-.1pt"></span></span></span></span></span><br> <b><span lang="EN-IN" style="font-size:9.0pt"><span style="background:#2d7f8f"><span style="color:white">Results: </span></span></span></b><span style="font-size:9.0pt">The susceptibility tests for discs were performed following the guidelines outlined by the Clinical Laboratory Standards Institute in 2023 (CLSI). <i>K. pneumoniae</i> exhibits inherent resistance to ampicillin, while 80 (80%) strains of <i>E. coli</i> have been reported to be resistant to ampicillin. Additionally, 50 <i>K. pneumoniae</i> isolates and 41 <i>E. coli</i> isolates were found capable of forming a biofilm. Seven of <i>E. coli</i> (17.07%), and seven of <i>K. pneumoniae</i> (14%) isolates could form a mighty biofilm. It was observed that the strongest resistance in the isolates that formed strong biofilm was related to tetracycline with 5 (7.2%) resistance in <i>K. pneumonia </i>and 7 (7%) resistance in <i>E. coli</i>. Furthermore, 47 (47%) of <i>E. coli</i>, and 21 (20.2%) of <i>K. pneumoniae</i> isolates were classified as ESBLs producers, and 52 (50%) <i>K. pneumoniae</i> and 72 (72%) <i>E. coli</i> isolates were classified as MDR.</span><br> <span style="font-size:9.0pt"></span><br> <b><span style="font-size:9.0pt"><span style="background:#2d7f8f"><span style="color:white">Conclusion: </span></span></span></b><span style="font-size:9.0pt">Considering the role of biofilm in the transfer of genes, appropriate health policies, and the correct administration of effective antibiotics can help in prevention.</span><br> &nbsp; Escherichia coli, Klebsiella pneumoniae, Antibiotic-resistant, Biofilm, ESBLs, MDR 219 225 http://journal.zums.ac.ir/browse.php?a_code=A-10-5288-6&slc_lang=en&sid=1 Bahman Mirzaei dr.bahman.m@gmail.com 5200319475328460089428 5200319475328460089428 Yes Department of Medical Microbiology and Virology, School of Medicine, Zanjan University of Medical Science, Zanjan, Iran