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Class I integrons have garnered significant attention due to pivotal roles in the dissemination of antimicrobial resistance genes (ARGs), which impose risks to public health and food safety. Here, the prevalence and characteristics of class I integrons in Escherichia coli isolates derived from food-producing animals and human patients were assessed. Of 721 E. coli isolates collected from human patients (113), pigs (298), and poultry (310), 93 (12.90%) carried the class I integrase gene (intI1). Multilocus sequence typing identified 39 sequence types from 93 intI1-postive isolates, including three novel types. Sequence analysis revealed that 59 classical class I integrons encompassed six distinct gene cassettes arrangements [dfrA17-aadA5, dfrA12-aadA2, dfrA1-aadA1, dfrA7, aac(6')-Ib, and aadA1-aac(3)-VIa]. Six insertion sequences (IS1, IS6, IS21, IS91, IS110, and IS256) and one transposon (Tn3) were harbored in proximity to the integrons. A comparison with sequences retrieved from the National Center for Biotechnology Information database demonstrated that E. coli isolates with integron sequences were detected in various food-producing animals and human hosts in environmental niches across Asia, Europe, and North America. These findings indicate the potential risk of ARG transmission between food-producing animals and humans by bacteria populations and provide useful baseline data for monitoring of ARGs. [ABSTRACT FROM AUTHOR]

Background: Productions of metallo-β-lactamases enzymes are the most common mechanism of antibiotic resistance to all beta-lactam classes (except monobactams) in Acinetobacter baumannii. MBLs are usually associated with gene cassettes of integrons and spread easily among bacteria. The current study was performed to detect the genes encoding MBLs and integron structures in A. baumannii isolates from burn patients.Methods: This study was performed on 106 non-duplicate A. baumannii isolates from burn patients referred to Shahid Motahari Hospital in Tehran. Antibiotic susceptibility of A. baumannii isolates was performed using disk diffusion and broth microdilution method in accordance with the CLSI guidelines. The presence of class 1 integron and associated gene cassettes as well as MBLs-encoding genes including blaVIM, and blaIMP were investigated using PCR and sequencing techniques.Results: In this cross-sectional study all (100%) of the A. baumannii isolates examined were multidrug resistant. All isolates were sensitive to colistin and simultaneously all were resistant to imipenem. PCR assays showed the presence of blaVIM and blaIMP genes in 102 (96.2%) and 62 (58.5%) isolates of A. baumannii respectively. In addition, 62 (58.5%) of the A. baumannii isolates carried integron class 1, of which 49 (79.0%) were identified with at least one gene cassette. Three types of integron class 1 gene cassettes were identified including: arr2, cmlA5, qacE1 (2300 bp); arr-2, ereC, aadA1, cmlA7, qacE1 (4800 bp); and aac(3)-Ic, cmlA5 (2250 bp).Conclusion: A high prevalence of MBLs genes, especially blaVIM, was identified in the studied MDR A. baumannii isolates. In addition, most of the strains carried class 1 integrons. Furthermore, the gene cassettes arrays of integrons including cmlA5 and cmlA7 were detected, for the first time, in A. baumannii strains in Iran. [ABSTRACT FROM AUTHOR]

Background: Integrons are genomic elements that mediate horizontal gene transfer by inserting and removing genetic material using site-specific recombination. Integrons are commonly found in bacterial genomes, where they maintain a large and diverse set of genes that plays an important role in adaptation and evolution. Previous studies have started to characterize the wide range of biological functions present in integrons. However, the efforts have so far mainly been limited to genomes from cultivable bacteria and amplicons generated by PCR, thus targeting only a small part of the total integron diversity. Metagenomic data, generated by direct sequencing of environmental and clinical samples, provides a more holistic and unbiased analysis of integron-associated genes. However, the fragmented nature of metagenomic data has previously made such analysis highly challenging. Results: Here, we present a systematic survey of integron-associated genes in metagenomic data. The analysis was based on a newly developed computational method where integron-associated genes were identified by detecting their associated recombination sites. By processing contiguous sequences assembled from more than 10 terabases of metagenomic data, we were able to identify 13,397 unique integron-associated genes. Metagenomes from marine microbial communities had the highest occurrence of integron-associated genes with levels more than 100-fold higher than in the human microbiome. The identified genes had a large functional diversity spanning over several functional classes. Genes associated with defense mechanisms and mobility facilitators were most overrepresented and more than five times as common in integrons compared to other bacterial genes. As many as two thirds of the genes were found to encode proteins of unknown function. Less than 1% of the genes were associated with antibiotic resistance, of which several were novel, previously undescribed, resistance gene variants. Conclusions: Our results highlight the large functional diversity maintained by integrons present in unculturable bacteria and significantly expands the number of described integron-associated genes. [ABSTRACT FROM AUTHOR]

Background: VIM-type enzyme encodes the most widely acquired metallo-β-lactamases in Gram-negative bacteria. To obtain current epidemiological data for integrons from enterobacteriae in hospital, the study characterizes the genetic structure in In1059 by comparison with In846 integrons harbouring VIM gene and other class 1 integrons including In37, In62, In843 and In1021 with the aim of identifying the putative mechanisms involved integron mobilization and infer evolution of relevant integrons. Methods: Six of 69 recombinant plasmids from clinical strains were found to be class 1 integrons by digestion with BamHI, drug susceptibility testing, conjugation experiments, PCR amplification, integron cloning and sequencing, genome comparison, and detection of carbapenemase activity. Results: The sequences of the six recombinant plasmids encoding In1021, In843, In846, In37, In62, and the novel In1059 integron had approximate lengths of ~4.8-, 4.1-, 5.1-, 5.3-, 5.3- and 6.6- kb, respectively. The genetic structures of these integrons were mapped and characterized, and the carbapenemase activities of their parental strains were assessed. Conclusions: Our results suggest that the six variable integron structures and regular variations that exist in the gene cassettes provide a putative mechanism for the integron changes. Our study has also shown that the genetic features in the integrons named above fall within a scheme involving the stepwise and parallel evolution of class 1 integron variation likely under antibiotic selection pressure in clinical settings. [ABSTRACT FROM AUTHOR]

Background: Dystroglycan (DG) is an adhesion receptor complex composed of two non-covalently associated subunits, transcribed from a single gene. The extracellular α-DG is highly and heterogeneously glycosylated and binds with high affinity to laminins, and the transmembrane β-DG binds intracellular dystrophin. Multiple cellular functions have been proposed for DG, notwithstanding that its role in skeletal muscle appears central as demonstrated by both primary and secondary severe muscular dystrophic phenotypes collectively known as dystroglycanopathies. We recently analysed the molecular phylogeny of the DG core protein and identified the α/β interface, transmembrane and cytoplasmic domains of β-DG as the most conserved region. It was also identified that the IG2_MAT_NU region has been independently duplicated in multiple lineages. Results: To understand the evolution of dystroglycan in more depth, we investigated dystroglycan gene structure in 35 species representative of the phyla in which dystroglycan has been identified (i.e., all metazoan phyla except Ctenophora). The gene structure of three exons and two introns is remarkably conserved. However, additional lineagespecific introns were identified, which interrupt the coding sequence at distinct points, were identified in multiple metazoan groups, most prominently in ecdysozoans. Conclusions: A coding DNA sequence (CDS) intron that interrupts the encoding of the IG1 domain is universally conserved and this intron is longer in gnathostomes (jawed vertebrates) than in other metazoans. Lineage-specific gain of additional introns has occurred notably in ecdysozoans, where multiple introns interrupt the large 3' exon. More limited intron gain has also occurred in placozoa, cnidarians, urochordates and the DG paralogues of lamprey and teleost fish. [ABSTRACT FROM AUTHOR]

Background: Although CRISPR/Cas enables one-step gene cassette knock-in, assembling targeting vectors containing long homology arms is a laborious process for high-throughput knock-in. We recently developed the CRISPR/Cas-based precise integration into the target chromosome (PITCh) system for a gene cassette knock-in without long homology arms mediated by microhomology-mediated end-joining. Results: Here, we identified exonuclease 1 (Exo1) as an enhancer for PITCh in human cells. By combining the Exo1 and PITCh-directed donor vectors, we achieved convenient one-step knock-in of gene cassettes and floxed allele both in human cells and mouse zygotes. Conclusions: Our results provide a technical platform for high-throughput knock-in. [ABSTRACT FROM AUTHOR]

Background: The human and animal intestinal tract harbors a complex community of microbes which enables bacteria to inherit antibiotic resistance genes. The aims of this study were to investigate clonality, antimicrobial resistance, prevalence and gene cassette arrays of class I and II integrons among commensal Escherichia coli from human and animals. Methods: A total of 200 E. coli isolates from human, chicken, cattle, and sheep were isolated followed by phenotypic antibiotic susceptibility testing and detection of class I and II integrons gene cassettes arrays. The clonal relationship of the isolates were analyzed by (GTG)5-PCR. Results: Of 200 isolates, 136 isolates were multi drug resistance (MDR) including 47, 40, 31 and 18 isolates from chicken, human, cattle and sheep, respectively. Class I integron was detected in 50, 38, 6 and 16%, while class II was detected in 26, 8, 0 and 4% of chicken, human, cattle and sheep isolates, respectively. Variable regions were amplified and sequenced. Cassette arrays in class I integrons were: dfrA1, dfrA5, dfrA7, dfrA12, aadA1, dfrA17 aadA1, aadA22, aadB-aadA2 and dfrA12-orfF-aadA2, and for class II, dfrA1-sat-aadA1, and sat-sat1-aadA1 were detected. Six class I and three class II positive strains did not produce any amplicons for variable region. Integron-positive isolates showed higher rate of resistance to streptomycin and trimethoprim-sulphamethoxazole, especially in chicken isolates which were fed antibiotics. Low similarity and great genetic diversity of class I and II integrons carrying isolates indicated no clonal relation. Conclusions: Integrons encoding for antibiotic resistance are significantly present among non-pathogenic commensal E. coli, especially from the hosts medicated by antibiotics. Uncontrolled use of antibiotics will increase the numbers of multiple drug resistant isolates and integrons prevalence. [ABSTRACT FROM AUTHOR]

Background: The classic AOX1 replacement approach is still one of the most often used techniques for expression of recombinant proteins in the methylotrophic yeast Pichia pastoris. Although this approach is largely successful, it frequently delivers clones with unpredicted production characteristics and a work-intense screening process is required to find the strain with desired productivity. Results: In this project 845 P. pastoris clones, transformed with a GFP expression cassette, were analyzed for their methanol-utilization (Mut)-phenotypes, GFP gene expression levels and gene copy numbers. Several groups of strains with irregular features were identified. Such features include GFP expression that is markedly higher or lower than expected based on gene copy number as well as strains that grew under selective conditions but where the GFP gene cassette and its expression could not be detected. From these classes of strains 31 characteristic clones were selected and their genomes sequenced. By correlating the assembled genome data with the experimental phenotypes novel insights were obtained. These comprise a clear connection between productivity and cassette-to-cassette orientation in the genome, the occurrence of false-positive clones due to a secondary recombination event, and lower total productivity due to the presence of untransformed cells within the isolates were discovered. To cope with some of these problems, the original vector was optimized by replacing the AOX1 terminator, preventing the occurrence of false-positive clones due to the secondary recombination event. Conclusions: Standard methods for transformation of P. pastoris led to a multitude of unintended and sometimes detrimental integration events, lowering total productivity. By documenting the connections between productivity and integration event we obtained a deeper understanding of the genetics of mutation in P. pastoris. These findings and the derived improved mutagenesis and transformation procedures and tools will help other scientists working on recombinant protein production in P. pastoris and similar non-conventional yeasts. [ABSTRACT FROM AUTHOR]

Background: blaVIM-2 harboring Pseudomonas aeruginosa has been reported worldwide and considered as the most prevalent metallo-β-lactamase after NDM which are found horizontally transferable and mostly associated with integron gene cassettes. The present study investigates the genetic background, transmission dynamics as well as stability of blaVIM-2 in clinical isolates of P. aeruginosa harbor blaNDM-1 as well which were collected from October 2012 to September 2013. Methods: Two P. aeruginosa strains harboring blaVIM-2 along with blaNDM-1 were isolated from Silchar Medical College and Hospital, India. Genetic environment of these resistance determinants was determined and transferability was checked by transformation and conjugation assay which was further confirmed by Southern hybridization. Replicon typing was performed to determine the incompatibility group of the resistant plasmid and their stability was checked by serial passage method. Antimicrobial susceptibility pattern of the isolates was determined and their clonal relatedness was checked by pulsed field gel electrophoresis. Results: blaVIM-2 was found to be horizontally transferable through an Inc F type plasmid of approximately 30 kb in size. blaVIM-2 was found to be associated with integron gene cassette and was flanked by two different types of cassette arrays. Both the isolates were co-harboring blaNDM-1 which was carried within Inc N type of plasmid with an approximate 24 kb in size and associated with ISAba125 in their upstream region. Reduced susceptibility rate as well as high MIC range was observed in case of wild strains and transformants carrying blaVIM-2 and blaNDM-1. Conclusions: The detection of this co-existence of multiple carbapenem resistance genes in this part of world is worrisome and further investigation is required in order to trace the source and to initiate proper treatment option. [ABSTRACT FROM AUTHOR]

Background: To investigate antibiotic resistance, the occurrence and distribution of class 1 and 2 integrons in multidrug- resistant Staphylococcus aureus isolates from hospitals in Tehran, Iran. The isolates were examined for susceptibility to antimicrobial agents. The mecA gene, class 1 and 2 integrons were detected by PCR. Integrase positive strains were further analysed for the presence of resistance gene cassettes using specific primers and were sequenced. Results: Among 139 S.aureus isolates, 109 (78.4 %) and 112 (80.5 %) strains were considered as multidrug resistant and mecA positive, respectively. Class 1 integrons and internal variable regions were found in 72.6 % (101/139) and 97 % (98/101) and class 2 integrons and variable regions also in 35.2 % (49/139) and 65.3 % (32/49) of S.aureus clinical isolates, respectively. Twelve distinct cassette arrays were found, containing genes encoding resistance to ß-lactams, aminoglycosides, streptothricin, trimethoprim, chloramphenicol,a putative glucose dehydrogenase precursor and a protein with unknown function. Gene cassette arrays aadB, aadA2 and dhfrA1-sat2-aadA1 were common in S.aureus isolates. We detected a completely new gene cassettes which contained aadB, oxa2, aacA4, orfD-aacA4-catB8, aadB-catB3, orfD-aacA4 and aadB-aadA1-cmlA6 of class 1 and dhfrA1-sat2-aadA1, dhfrA11, dhfrA1-sat2 of class 2 integrons. Conclusions: This is the first study to report carriage of class 1 and 2 integrons and associated gene cassettes among in S.aureus isolates from Iran. [ABSTRACT FROM AUTHOR]

Background Laribacter hongkongensis is a Gram-negative, urease-positive bacillus associated with invasive bacteremic infections in liver cirrhosis patients and fish-borne community-acquired gastroenteritis and traveler's diarrhea. Its mechanisms of adaptation to various environmental niches and host defense evasion are largely unknown. During the process of analyzing the L. hongkongensis genome, a complete urease cassette and two adjacent arc gene cassettes were found. We hypothesize that the urease cassette and/or the arc gene cassettes are important for L. hongkongensis to survive in acidic environment and macrophages. In this study, we tested this hypothesis by constructing single, double and triple non-polar deletion mutants of the urease and two arc gene cassettes of L. hongkongensis using the conjugation-mediated gene deletion system and examining their effects in acidic environment in vitro, in macrophages and in a mouse model. Results HLHK9ΔureA, HLHK9ΔureC, HLHK9ΔureD and HLHK9ΔureE all exhibited no urease activity. HLHK9ΔarcA1 and HLHK9ΔarcA2 both exhibited arginine deiminase (ADI) activities, but HLHK9ΔarcA1/arcA2 double deletion mutant exhibited no ADI activity. At pH 2 and 3, survival of HLHK9ΔarcA1/arcA2 and HLHK9ΔureA/arcA1/arcA2 were markedly decreased (p < 0.001) but that of HLHK9ΔureA was slightly decreased (p < 0.05), compared to wild type L. hongkongensis HLHK9. Survival of HLHK9ΔureA/arcA1/arcA2 and HLHK9ΔarcA1/arcA2 in macrophages were also markedly decreased (p < 0.001 and p < 0.01 respectively) but that of HLHK9ΔureA was slightly decreased (p < 0.05), compared to HLHK9, although expression of arcA1, arcA2 and ureA genes were all upregulated. Using a mouse model, HLHK9ΔureA exhibited similar survival compared to HLHK9 after passing through the murine stomach, but survival of HLHK9ΔarcA1/arcA2 and HLHK9ΔureA/arcA1/arcA2 were markedly reduced (p < 0.01). Conclusions In contrast to other important gastrointestinal tract pathogens, ADI pathway is far more important than urease for acid resistance and intracellular survival in L. hongkongensis. The gene duplication of the arc gene cassettes could be a result of their functional importance in L. hongkongensis. [ABSTRACT FROM AUTHOR]

Background The recombinant yeast strains displaying the heterologous cellulolytic enzymes on the cell surface using the glycosylphosphatidylinositol (GPI) anchoring system are considered promising biocatalysts for direct conversion of lignocellulosic materials to ethanol. However, the cellulolytic activities of the conventional cellulase-displaying yeast strains are insufficient for the hydrolysis of cellulose. In this study, we constructed novel gene cassettes for the efficient cellulose utilization by cellulase-displaying yeast strains. Results The novel gene cassettes for the cell-surface display of Aspergillus aculeatus β-glucosidase (BGL1) and Trichoderma reeseii endoglucanase II (EGII) were constructed using the promoter and the GPI anchoring region derived from Saccharomyces cerevisiae SED1. The gene cassettes were integrated into the S. cerevisiae genome, then the β-glucosidase activity of these recombinant strains was evaluated. We revealed that simultaneous utilization of the SED1 promoter and Sed1 anchoring domain in a gene cassette enabled highly-efficient enzyme integration into the cell wall. The β-glucosidase activity of recombinant yeast cells transduced with the novel gene cassette was 8.4-fold higher than that of a conventional strain. The novel EGII-displaying strain also achieved 106-fold higher hydrolysis activity against the water-insoluble cellulose than a conventional strain. Furthermore, direct ethanol production from hydrothermally processed rice straw was improved by the display of T. reeseii EGII using the novel gene cassette. Conclusions We have developed novel gene cassettes for the efficient cell-surface display of exo- and endo-type cellulolytic enzymes. The results suggest that this gene cassette has the wide applicability for cell-surface display and that cellulase-displaying yeasts have significant potential for cost-effective bioethanol production from lignocellulosic biomass. [ABSTRACT FROM AUTHOR]

Background Multidrug-resistant Pseudomonas aeruginosa is a serious challenge for antimicrobial therapy of nosocomial infections, as it possesses several mechanisms of antimicrobial resistance. In Central Greece, a sudden increase of infections caused by carbapenem-resistant P. aeruginosa was observed during 2011, indicating the need for further analysis. Methods Five-hundred and sixty-eight P. aeruginosa isolates were collected consecutively during an 8-month period in 2011 from inpatients treated in three hospitals in the Thessaly region (1,000,000 habitants) of Greece. Carbapenem-resistant P. aeruginosa (n = 284) were characterized by antimicrobial susceptibility testing and β-lactamase content, and the genetic relatedness of carbapenemase-producing isolates was assessed by BOX-PCR, multilocus sequence typing, and eBURST analysis. Mapping of the class I integrons of Verona integronencoded metallo-β-lactamase (VIM)-carrying isolates was also performed, and clinical data of the VIM producers were reviewed. Results Eighty (14.1%) out of the 568 P. aeruginosa isolates recovered from clinical specimens were VIM producers. Multilocus sequence typing revealed high prevalence of the international clones ST111 and ST235 among blaVIM-2- and blaVIM-4-positive isolates, respectively. blaVIM-17 was identified in an isolate of a novel sequence type (ST1457). blaVIM gene cassettes were carried by five distinct class I integrons, including two novel ones. Conclusions Since the first report of VIM-producing P. aeruginosa in 2000, this microorganism still remains among the most prevalent multidrug resistant pathogens in Greece. The spread of VIM-producers belonging to the most common international clones (ST111 and ST235), the spread of integrons of divergent structures, and the emergence of novel integrons underscore their ongoing evolution. [ABSTRACT FROM AUTHOR]

Background Antibiotic/ herbicide resistant marker genes have been proven to be very useful in plant transformation for the initial selection of desired transgenic events. However, presence of these genes in the genetically modified crops may render the crop less acceptable to the consumers. Among several different approaches, the effectiveness of Cre/lox mediated recombination strategy for selectable marker gene (SMG) elimination has previously been demonstrated by different groups in several plants including Brassica. In the present study exploiting Cre/lox mediated recombination strategy, attempt has been made for selectable marker gene elimination from Allium sativum leaf agglutinin (ASAL) expressing Brassica plants with hemipteran insect resistant phenotype. Results Allium sativum leaf agglutinin (ASAL) linked with lox flanked hygromycin resistant (hpt) gene was introduced in mustard. Cre recombinase gene cassette was also integrated in separate event. A Cre/lox mediated recombination using crossing strategy was adopted to remove the hpt gene from the subsequent generation of selected hybrid events. Reciprocal crosses were made between T1 ASAL-lox-hpt-lox and cre-bar plants. Marker gene elimination was confirmed in the resulting F1 hybrid progenies by PCR analysis, using hpt, cre and ASAL specific primers followed by Southern hybridization. In marker free plants, expression of ASAL was also confirmed by western blotting and ELISA analysis. Retention of functionality of expressed ASAL was investigated by agglutination assay using rabbit erythrocytes. Expressed ASAL was also found to be thermo-sensitive. In planta insect bioassay on F1 hybrid progenies exhibited detrimental effect on the performance of devastating target pest, Lipaphis erysimi. The F1 hybrid hpt negative, ASAL positive plants were allowed to self- fertilize to obtain F2 progeny plants. In some of these plants cre gene was found to be segregated out of the ASAL gene by genetic segregation yielding completely marker free plants. Conclusions The present study establishes the efficient expression of the newly introduced insect resistant ASAL gene even after Cre/lox mediated recombination resulting in elimination of selectable marker gene. [ABSTRACT FROM AUTHOR]

Background Multidrug resistant Pseudomonas aeruginosa harbours integrons and other mobile genetic elements such as plasmids and transposons, which easily disseminate antibiotic resistance genes among clinical strains of P. aeruginosa. Methodology Plasmid extraction of 54 clinical isolates of P. aeruginosa was carried out by alkaline lysis method; and plasmid size estimation was done by using E. coli V517 standard plasmid marker. Fifty-four clinical strains of P. aeruginosa were isolated from 5 hospitals in 3 Southwestern states of Nigeria between March and September 2010. Plasmid extraction of isolates was carried out by alkaline lysis method; and plasmid size estimation was done by using E. coli V517 standard plasmid marker. PCR amplification for the 3 classes of resistance integrons, and gene cassette characterization were carried out using specific primers and by sequencing of PCR products. Conjugal mating of the integron positive P. aeruginosa strains with E. coli DH5α was performed to demonstrate transferability of integrons and gene cassettes. Result Agarose gel electrophoresis of plasmid DNA revealed that all the 54 P. aeruginosa harboured 1-4 plasmids with sizes ranging from 2.2 - >58 kb. Class 1 integron was identified in 31 (57%) strains; but none of them carried class 2 and class 3 integrons. High prevalence of aadA gene conferring resistance to streptomycin/spectinomycin was detected in the strains positive for class 1 integron. Sequencing of the 1.6 kb and 1.2 kb amplified band of gene cassettes revealed the presence of aadA6-orfD and aadA13 respectively. Conclusion This study demonstrates the presence of plasmids and integrons harbouring resistance gene cassettes, which may collectively constitute an efficient system for dissemination of resistance genes in P. aeruginosa. Disturbingly, the rapid and unabated spread of class 1 integron-associated multidrug resistant P. aeruginosa in Southwest Nigeria may greatly hamper successful treatment of infections caused by such strains. This necessitates the establishment of functional antimicrobial resistance surveillance programmes in Nigeria. [ABSTRACT FROM AUTHOR]

Background: Integrons are mobile DNA elements and they have an important role in acquisition and dissemination of antimicrobial resistance genes. However, there are limited data available on integrons of Staphylococcus aureus (S. aureus) from bovine mastitis, especially from Chinese dairy cows. To address this knowledge gap, bovine mastitis-inducing S. aureus isolates were investigated for the presence of integrons as well as characterization of gene cassettes. Integrons were detected using PCR reactions and then further characterized by a restriction fragment-length polymorphism analysis and amplicon sequencing. Results: All 121 S. aureus isolates carried the class 1 integrase gene intI1, with no intI2 and intI3 genes detected. One hundred and three isolates were positive for the presence of 12 resistance genes, either alone or in combination with other gene cassettes. These resistance genes encoded resistance to trimethoprim (dhfrV, dfrA1, dfrA12), aminoglycosides (aadA1, aadA5, aadA4, aadA24, aacA4, aadA2, aadB), chloramphenicol (cmlA6) and quaternary ammonium compound (qacH) and were organized into 11 different gene cassettes arrangements (A-K). The gene cassette arrays dfrA1-aadA1 (D, 44.6%), aadA2 (K, 31.4%), dfrA12-orfX2-aadA2 (G, 27.3%) and aadA1 (A, 25.6%) were most prevalent. Furthermore, 74 isolates contained combinations of 2 to 4 gene cassette arrays. Finally, all of the integron/cassettes-positive isolates were resistant to aminoglycoside antibiotics. Conclusions: This is the first study on the integrons and gene cassette arrays in S. aureus isolates from milk of mastitic cows from Northwestern China and provide the evidence for class 1 integron as possible antibiotic resistance determinants on dairy farms. [ABSTRACT FROM AUTHOR]