A survey of 187 clinical Pseudomonas aeruginosa isolates from four hospitals in Qom province, central Iran, has found that 73 isolates carried Class 1 integrons and 14 carried Class 2 integrons, corresponding to prevalences of 39% and 7.5%, respectively. None of the isolates contained Class 3 integrons. The findings, published in MicrobiologyOpen, come from a cross-sectional molecular analysis of bacteria recovered from hospitalized patients aged 20 to 86 who were suspected of having nosocomial infections, and they map which mobile genetic platforms for antibiotic resistance genes are present in this collection of clinical isolates.
Integrons are genetic platforms capable of capturing, rearranging, and expressing gene cassettes, including antimicrobial resistance determinants, thereby facilitating the emergence and dissemination of multidrug-resistant bacteria. Unlike plasmids, integrons themselves are not necessarily self-replicating genetic elements; rather, they can occur within different genetic contexts. In clinical bacteria, particularly mobile Class 1 and 2 integrons, integron structures may be associated with plasmids, transposons, or the bacterial chromosome, providing an important mechanism for the acquisition and horizontal dissemination of resistance gene cassettes. These resistance genes are housed within mobile cassettes that can be shuffled and exchanged between integrons, enabling bacteria to rapidly evolve and adapt to various antibiotics.
The isolates analyzed were a subset of a previously described collection of 200 nonduplicated clinical P. aeruginosa isolates gathered from Shahid Beheshti, Nekoei, Kamkar, and Valiasr Hospitals, all affiliated with Qom University of Medical Sciences. Of the original 200, 187 were included in the present study, distributed approximately equally across the four hospitals: 91 isolates from Shahid Beheshti, 53 from Nekoei, 32 from Kamkar, and 11 from Valiasr. The samples came from urine, blood, surgical wounds, burn wounds, feces, and general body secretions including ear, eyes, nose, and sputum. Before molecular work began, the stored isolates were confirmed through Gram staining and a battery of biochemical tests, including oxidase and indole tests, culture on Simmons’ citrate agar, triple sugar iron agar, the sulfur indole motility test, and methyl red-Vegesproskaure assays.
To detect the integrons, the researchers extracted genomic DNA using a boiling method and screened every isolate by polymerase chain reaction with primers specific to the intI1, intI2, and intI3 integrase genes. Positive controls for each reaction were well-characterized Escherichia coli strains carrying known integrons: strain UB1637 with plasmid pR388:In3 for Class 1, strain DH5α with pMAQ612:Tn7 for Class 2, and strain DH5α with pSMB731 for Class 3, while E. coli ATCC 25922 served as the negative control. Amplified products were visualized on agarose gels, with a distinct 457 bp band confirming intI1 and a 288 bp band confirming intI2. Among the 14 isolates harboring Class 2 integrons, 11 isolates, or 5.9% of the total, possessed both Class 1 and Class 2 integrons simultaneously; these dual carriers came from burn departments with a frequency of five isolates, special care with four isolates, and other departments with two isolates.
The antibiotic susceptibility of all 187 isolates was tested by the Kirby-Bauer disk diffusion method against 18 antibiotics according to Clinical and Laboratory Standards Institute guidelines. Resistance rates were high across many drug classes: 50.8% to imipenem, 51.3% to ceftazidime, 63.6% to cefotaxime, 29.4% to amikacin, 46.5% to gentamicin, 81.3% to ceftizoxime, 27.8% to piperacillin-tazobactam, 34.8% to meropenem, 0.38% to piperacillin, and 50.3% to ceftriaxone. Resistance frequencies to ciprofloxacin, aztreonam, ticarcillin, tobramycin, cefepime, and ticarcillin-clavulanic acid were 46.5%, 43.9%, 43.9%, 47.1%, 38.5%, and 49.2%, respectively. Isolates resistant to colistin and polymyxin B constituted 16.0% and 3.7% of the collection.
When the researchers stratified resistance by integron status, the picture was more nuanced than a simple association. Among the 73 intI1-positive isolates, resistance to imipenem was 57% compared with 46% in the 114 intI1-negative isolates, and resistance to ceftizoxime reached 85% versus 79%. For the 14 intI2-positive isolates, resistance to imipenem was 79% and to gentamicin 71%, higher than the 49% and 44% seen in intI2-negative isolates. However, when the data were subjected to a Chi-square test evaluating the relationship between different resistance patterns and the presence of these integrons, the results showed no significant correlation of resistance patterns with the presence of Class 1 and 2 integrons in the clinical isolates. Among the 154 isolates classified as multidrug-resistant, extensively drug-resistant, or pan-drug-resistant, 66 isolates, or 42.9%, were found to harbor the Class 1 integron.
Beyond simply detecting the integrons, the team probed the variable regions of the Class 1 integrons in the 73 intI1-positive isolates, using conserved-region primers that flank the gene-cassette array. Short products representing only the structural backbone of the integron were not considered informative, but larger amplicons indicated inserted gene cassettes. Two isolates produced an approximately 800 bp amplicon, 11 produced an approximately 1700 bp amplicon, and six produced an approximately 2200 bp amplicon, making the 1700 bp product the most frequently detected, followed by the 2200 and 800 bp products. The remaining 54 intI1-positive isolates produced no detectable informative variable-region amplicon under the PCR conditions used, a result the authors caution does not necessarily demonstrate the absence of gene cassettes, because sequence variation at primer-binding sites or other PCR-related factors may interfere with amplification.
Bidirectional sequencing of representative fragments from each size category revealed the cassette arrangements carried by these integrons. The 800 bp fragment matched the coding sequence of the aminoglycoside 2′-O-adenylyl transferase aadB gene, with the surrounding integron structure comprising the intI1 gene, the attI1 promoter, the aadB cassette, a 59-base element, the quaternary ammonium compound resistance gene, sul1, and ORF5. The 1700 bp fragment contained the beta-lactamase blaOXA-10 gene together with the aminoglycoside 6′-N-acetyltransferase aac(6′)-II gene, an arrangement documented in GenBank under accession KX241477. The 2200 bp fragment carried three resistance genes in sequence: aadB, blaOXA-10, and aac(6′)-Ib, corresponding to accession KU839731. Together, these cassettes encode aminoglycoside-modifying enzymes and Class D beta-lactamases, or oxacillinases, which hydrolyze the beta-lactam ring of penicillin and cephalosporin family antibiotics.
The authors are explicit about the limits of what these prevalence figures can show. Because no molecular typing was performed, the study cannot determine the clonal relatedness of the isolates or establish whether the observed prevalence resulted from clonal expansion, independent acquisition, or dissemination of resistance determinants. The relatively high prevalence of Class 1 integrons may reflect circulation of resistance determinants among genetically diverse isolates, the expansion of one or more successful clones, or a combination of both. The observed distribution of integron-positive isolates across clinical settings, including burn and special-care units, is descriptive and does not establish epidemiological linkage between patients or wards, and the findings should not be interpreted as direct evidence of intrahospital transmission or regional clonal dissemination.
Future investigations, the team notes, should incorporate molecular epidemiological approaches such as RAPD-PCR, PFGE, MLST, or preferably whole-genome sequencing to establish the genetic relatedness of isolates and to clarify whether clusters of integron-positive P. aeruginosa reflect clonal transmission or independent acquisition of mobile resistance determinants. Integrating bacterial typing with temporal, patient-level, ward-level, and environmental sampling would provide a more robust assessment of possible transmission pathways within healthcare settings. For now, the study stands as an estimate of integron occurrence among sampled clinical P. aeruginosa isolates from central Iran, documenting that Class 1 integrons carrying aminoglycoside and beta-lactam resistance cassettes are common in this collection, Class 2 integrons appear at low frequency, and Class 3 integrons were entirely absent.
Subject of Research: Prevalence and gene-cassettes of Class 1, 2, and 3 integrons in multidrug-resistant clinical Pseudomonas aeruginosa isolates from central Iran
Article Title: Dissemination of Class 1, 2, and 3 Integrons Among Multidrug‐Resistant Isolates of Pseudomonas aeruginosa
Article References: Hosseini Bafghi, M., Baghaie, A., & Nazari, R. (2026). Dissemination of Class 1, 2, and 3 Integrons Among Multidrug‐Resistant Isolates of Pseudomonas aeruginosa. MicrobiologyOpen, 15(6), Article e70447. https://doi.org/10.1002/mbo3.70447
Image Credits: AI Generated
DOI: 10.1002/mbo3.70447
Keywords: Pseudomonas aeruginosa, integrons, antibiotic resistance, multidrug resistance, gene cassettes, hospital-acquired infections, Iran, PCR, DNA sequencing, aminoglycoside resistance, beta-lactamase, mobile genetic elements
News Source: Juliet Wilcox. (November 4, 2026). Class 1 and 2 Integrons Widespread in Multidrug-Resistant Pseudomonas aeruginosa From Iranian Hospitals. Scienmag.
