Integron Types Research Articles

Integron types, gene cassettes, antimicrobial resistance genes and plasmids of Shigella sonnei isolates from outbreaks and sporadic cases in Taiwan

This study analysed the presence, location and transferability of integrons and antibiotic resistance genes in 103 Shigella sonnei outbreak isolates and in 32 sporadic isolates from Taiwan. Multiple antimicrobial resistance was common in both outbreak (95 %) and sporadic (97 %) isolates. Class 1 integrons were present in 34 outbreak isolates (33 %) and in six sporadic isolates (19 %). This study is the first, to our knowledge, to identify an atypical sul3-associated class 1 integron carrying the estX-psp-aadA2-cmlA-aadA1-qacH cassette array in Shigella. Class 2 integrons carrying the dfr1-sat2-aadA1 cassette array were predominant in outbreak isolates (90 %) but were not present in sporadic isolates. Other antimicrobial resistance genes not associated with integrons were found to encode resistance to ampicillin (bla(TEM)), chloramphenicol (cat1), sulfonamide (sul2) and tetracycline (tetA and tetB). The most common plasmid size was 130 kb (observed in 43 and 97 % of 1998 outbreak and sporadic isolates, respectively). In conclusion, the plasmid location of resistance genes and horizontal plasmid transfer promote the spread of multiple resistance genes in outbreak and sporadic isolates of S. sonnei.

Transferable Class 1 and 2 Integrons inEscherichia coliandSalmonella entericaIsolates of Human and Animal Origin in Lithuania

Antibiotic-resistant Escherichia coli (n = 191) and Salmonella enterica (n = 87) isolates of human and animal origin obtained in Lithuania during 2005-2008 were characterized for the presence and diversity of class 1 and 2 integrons. E. coli isolates were obtained from patients with urinary tract infections (UTIs) (n = 59) and both healthy and diseased farm animals, including poultry (n = 54), swine (n = 35), and cattle (n = 43). Isolates of non-typhoidal S. enterica were recovered from salmonellosis patients (n = 37) and healthy animals, including poultry (n = 31) and swine (n = 19). The presence of integrons, their gene cassette structure, and genome location were investigated by polymerase chain reaction, restriction fragment-length polymorphism, DNA sequencing, Southern blot hybridization, and conjugation experiments. Forty percent of the E. coli and 11% of the S. enterica isolates carried class 1 integrons, whereas class 2 integrons were found in E. coli isolates (9%) only. The incidence of integrons in human UTIs and cattle isolates was most frequent (p < 0.01). A total of 23 different gene cassettes within 15 different variable regions were observed. Seven different integron types, all of them transferable by conjugation, were common for isolates from human infections and for one or more groups of animal isolates. The most prevalent integron types contained arrays dfrA1-aadA1 (36%), dfrA17-aadA5 (23%), and dfrA1-sat1-aadA1 (78%). Two E. coli isolates from humans with UTIs harbored class 1 integron on conjugative plasmid with the novel array type of 4800 bp/dfrA17-aadA5Δ-IS26-ΔintI1-aadB-aadA1-cmlA residing on the Tn21-like transposon. Three S. enterica isolates from swine contained class 1 integron with the newly observed array type of 1800 bp/aadA7-aadA7. Integrons of 10 different types of both classes were located on transferable plasmids in E. coli and S. enterica. Our study demonstrated the existence of a considerable and common pool of transferable integrons in E. coli and S. enterica present in clinical and livestock environment in Lithuania.

Antimicrobial Resistance, Class 1 Integrons, and Genomic Island 1 in Salmonella Isolates from Vietnam

BackgroundThe objective was to investigate the phenotypic and genotypic resistance and the horizontal transfer of resistance determinants from Salmonella isolates from humans and animals in Vietnam.Methodology/Principal FindingsThe susceptibility of 297 epidemiologically unrelated non-typhoid Salmonella isolates was investigated by disk diffusion assay. The isolates were screened for the presence of class 1 integrons and Salmonella genomic island 1 by PCR. The potential for the transfer of resistance determinants was investigated by conjugation experiments. Resistance to gentamicin, kanamycin, chloramphenicol, streptomycin, trimethoprim, ampicillin, nalidixic acid, sulphonamides, and tetracycline was found in 13 to 50% of the isolates. Nine distinct integron types were detected in 28% of the isolates belonging to 11 Salmonella serovars including S. Tallahassee. Gene cassettes identified were aadA1, aadA2, aadA5, bla PSE-1, bla OXA-30, dfrA1, dfrA12, dfrA17, and sat, as well as open reading frames with unknown functions. Most integrons were located on conjugative plasmids, which can transfer their antimicrobial resistance determinants to Escherichia coli or Salmonella Enteritidis, or with Salmonella Genomic Island 1 or its variants. The resistance gene cluster in serovar Emek identified by PCR mapping and nucleotide sequencing contained SGI1-J3 which is integrated in SGI1 at another position than the majority of SGI1. This is the second report on the insertion of SGI1 at this position. High-level resistance to fluoroquinolones was found in 3 multiresistant S. Typhimurium isolates and was associated with mutations in the gyrA gene leading to the amino acid changes Ser83Phe and Asp87Asn.ConclusionsResistance was common among Vietnamese Salmonella isolates from different sources. Legislation to enforce a more prudent use of antibiotics in both human and veterinary medicine should be implemented by the authorities in Vietnam.

Prevalence and Characterization of Class 1 Integrons inEscherichia coliof Poultry and Human Origin

A prospective study was conducted to determine the prevalence and the gene-cassette content of class 1 integrons in Escherichia coli of poultry and human origin. A total of 235 E. coli isolates were examined; 65 were derived from farm poultry, 80 from hospitalized, and 90 from nonhospitalized patients. Susceptibilities to a range of antimicrobial agents were determined by disk diffusion. Int1-specific polymerase chain reaction, conserved-segment polymerase chain reaction, and DNA sequencing were used to determine the presence, length, and content of integrons. The relatedness among the isolates was examined by pulsed-field gel electrophoresis of XbaI digests of genomic DNA. The integron carriage rate for poultry isolates was 49.2%, whereas the carriage rate for hospital isolates was 26.2% and for community 11.1%. Multidrug resistance (resistance to three or more classes of antibiotics) phenotypes were observed in 96.8% of the integron-positive isolates, whereas only 34.9% of nonintegron-carrying organisms were multidrug resistant (p < 0.001). Seven integron types ranging in size from 663 to 2674 bp were identified; six types were observed in poultry isolates, five in hospital, and three in community isolates. Each integron type carried a distinct gene-cassette combination. The most prevalent gene cassettes belonged to the aad and dfr families. Identical integrons were detected in E. coli of human and poultry origin. A large reservoir of integrons exists in E. coli of poultry origin. The horizontal transfer of class 1 integrons among bacteria of poultry and human origins may contribute in the dissemination of antimicrobial resistance.

Antibiotic resistance integrons and extended-spectrum -lactamases among Enterobacteriaceae isolates recovered from chickens and swine in Portugal

To investigate the diversity of integrons and extended-spectrum beta-lactamases (ESBLs) among Enterobacteriaceae from chickens and swine in Portugal and analyse the clonal relationships between Portuguese ESBL-producing isolates of animal and human origin. We analysed samples from faeces of healthy swine (HSF, n = 35), from uncooked chicken carcasses (CM, n = 20) and from faeces of healthy chickens (HCF, n = 20). Samples were plated on MacConkey agar with and without ceftazidime (1 mg/L) or cefotaxime (1 mg/L). ESBLs were characterized by PCR and DNA sequencing. Bacterial identification, antibiotic susceptibility and conjugation assays were performed by standard procedures. Isolate clonal relatedness was established by PFGE and by RAPD for PFGE non-typeable isolates. Escherichia coli phylogenetic groups were identified by a multiplex PCR. Integron analysis was accomplished by PCR-RFLP and sequencing. ESBL-producing Enterobacteriaceae were identified in 60% of CM, 10% of HCF and 5.7% of HSF samples, respectively, mostly corresponding to E. coli (phylogroups A, D and B1). TEM-52, SHV-2 and CTX-M-1 were detected from chicken and SHV-12 from swine samples. High clonal diversity was observed and most bla(ESBL) genes were transferable (67%). Class 1 and/or class 2 integrons were identified in 80% of CM, 10% of HCF and 63% of HSF samples, with class 1 integrons more common than class 2 integrons (36% versus 12% of the isolates recovered, respectively). Ten class 1 integron types are described, aadA1 and dfrA1-aadA1 being the most frequently found. Two class 1 integron types (aadA13-estX and dfrA14-aadA1-catB2) and one class 2 integron (aadA1) are first reported here. This study is the first report of ESBLs and integrons from chickens and swine in Portugal and highlights the antibiotic-resistant bacteria and/or resistance genes that might be acquired by humans through the food chain.

Molecular typing indicates an important role for two international clonal complexes in dissemination of VIM-producing Pseudomonas aeruginosa clinical isolates in Hungary

VIM metallo-β-lactamase-producing serotype O11 or O12 Pseudomonas aeruginosa isolates infecting or colonising 19 patients from seven hospitals were reported in Hungary between 2003 and 2005. In this study we characterised VIM-producing Pseudomonas spp. clinical isolates from two novel locations in Hungary; we identified three new bla VIM carrying integron types and the presence of the bla VIM-2 allele in Hungary. By applying various typing techniques, including multilocus sequence typing, we revealed an important role of two international clonal complexes, CC4 and CC11, in the dissemination of bla VIM-positive P. aeruginosa in hospitals in Hungary. Isolate P12-Q, a representative strain from France of the major European multiresistant P12 clone, displayed ST111 which, according to eBURST analysis, is the presently calculated founder sequence type of CC4. This is in accordance with the wide geographic distribution of the P12 clone. Our data indicate that, although the CC4 clonal complex includes serotype O1 and O6 isolates as well, it also contains the P12 clone. We characterised a P. aeruginosa nosocomial clone with a singleton sequence type (ST313), that may have acquired bla VIM-2 and bla VIM-4 gene cassettes from a yet unidentified local gene pool in Hungary.

Characterization of integrons-mediated antimicrobial resistance among Escherichia coli strains isolated from bovine mastitis

To assess the prevalence of antimicrobial resistance and class I integrons in Escherichia coli strains ( n = 58) isolated from bovine mastitis in Inner Mongolia, antimicrobial susceptibility and the presence of various types of integrons were characterized. Most isolates were susceptible to amikacin, colistin, ceftazidime, gentamicin and kanamycin, while those also exhibited high resistant incidence rates to ampicillin, amoxicillin, sulfadiazine and sulfamethoxydiazine. The integrase gene of integrons was amplified by PCR using degenerate primers. The integrons were confirmed by restriction fragment length polymorphism (RFLP) analysis of positive PCR products. Neither class II nor class III integron was detected, while 56.90% ( n = 33) of the isolates were positive for the presence of intI1 gene. Sequencing analysis of gene cassettes revealed that seven gene cassettes were found, which encoded resistance to trimethoprim ( dfrA1 and dfrA17), aminoglycosides ( aacA4, aadA1 and aadA5) and chloramphenicol ( catB3), respectively. Of them, the gene cassette array dfrA17– aadA5 was found most prevalent (62.96%). The percentage of positive-integron among the isolates whose resistant profile was relatively broad ( n ≥ 7) is 100.00%, while the one in narrow-profile isolates ( n = 2–6) is 30.56%. The correlation analysis revealed the incidence of integrons among the isolates were highly related to the resistant profile, indicating integrons play an important role in the dissemination and spread of the antimicrobial resistant strains.

A novel Salmonella genomic island 1 and rare integron types in Salmonella Typhimurium isolates from horses in The Netherlands

To investigate the genotypic resistance of integron-carrying Salmonella Typhimurium isolates from horses and their genetic relationship. Sixty-one Salmonella isolates were screened for the presence of class 1 integrons by PCR. The gene cassettes of integron-positive isolates were detected by PCR, restriction fragment length polymorphism typing, and sequencing. The potential for the transfer of resistance determinants was investigated by conjugation experiments. The presence of Salmonella genomic island 1 (SGI1) or its variants was studied by PCR and nucleotide sequencing. PFGE was used to genotype the isolates. Eight distinct XbaI-PFGE profiles and seven integron types were observed among 26 integron-carrying Salmonella Typhimurium isolates. The gene cassettes detected were dfrA1, dfrA7, dfrA14, aadA1, aadA2, aadB and bla(PSE). A rare type of integron found in nine isolates carried the dfrA14 and aadA1 gene cassettes. Twelve Salmonella Typhimurium DT104 isolates contained SGI1 or one of its variants (SGI1, SGI1-B and SGI1-C). A novel variant of SGI1, designated SGI1-M, was identified in one isolate in which the aadA2 gene of SGI1 was replaced by the aadB gene. Transfer of integrons and antimicrobial resistance determinants to Escherichia coli K12 via conjugation was possible with nine isolates. Resistance to fluoroquinolones in nine isolates was caused by mutations in the gyrA gene leading to the amino acid changes Ser-83 --> Ala and Asp-87 --> Asn. The integron-positive clinical Salmonella Typhimurium isolates from horses belong to distinct strains. The data demonstrate the capability of Salmonella Typhimurium to acquire additional antibiotic resistance determinants and underline the need for the prudent use of antimicrobials.

Dissemination of sul3 -Containing Elements Linked to Class 1 Integrons with an Unusual 3′ Conserved Sequence Region among Salmonella Isolates

A sul3 domain (IS440-sul3-orf1-IS26) was found linked to an unusual 3' conserved sequence region (qacH) of class 1 integrons and detected among nontyphoid Salmonella isolates (n=47) from different sources. Three types of integrons differing in the gene cassette array (dfrA12-orfF-aadA2-cmlA1-aadA1, dfrA12-orfF-aadA2/1, and estX-psp-aadA2-cmlA1-aadA1) were found associated with this sul3 domain. They were associated with particular clones and specific high-molecular-weight plasmids.

Presencia de Integrones Clase 1 en Aislamientos de Staphylococcus epidermidis de las unidades de neonatología del Instituto Materno Infantil de Bogotá

a multiresistencia a los antibióticos por bacterias Gram positivas, especialmente el Staphylococcus epidermidis, constituye un problema creciente de salud pública en las unidades neonatales. Uno de los mecanismos de resistencia bacteriana recientemente descrito es la presencia de integrones y cassettes genéticos. Existen más de 9 clases de integrones, siendo el de clase 1 el que con mayor frecuencia se encuentra implicado en cepas causantes de infección hospitalaria.En este estudio, se determinó la presencia de integrones clase 1 en Staphylococcus epidermidis, provenientes de hemocultivos y puntas de catéter, que causaron infección nosocomial en las unidades neonatales del Instituto Materno Infantil de Bogotá, Colombia. De las 46 cepas estudiadas, se detectó la presencia del gen intI 1 en 21 de los aislamientos (45.7%). Este hallazgo, pionero en cepas bacterianas aisladas en neonatos, sugiere la necesidad de buscar cassettes genéticos que confieren resistencia a los diferentes antimicrobianos, para definir esquemas de tratamiento de infecciones nosocomiales causadas por estos microorganismos.

Molecular differentiation of common promoters in Salmonella class 1 integrons

The integron is a mobile gene element which harbors antibiotic-resistance gene cassettes capable of site-specific integration. Among the four known types of integrons, the class 1 integron has been associated with multidrug-resistance in pathogenic bacteria. These gene cassettes have been the focus of a series of studies. The gene cassettes share a common promoter, and their expression levels are affected not only by their proximity to the promoter, but also by the strength (weak, hybrid and strong) of the common promoter, P1, as well as the presence of the additional promoter, P2. In this study, we developed molecular methods for the differentiation of promoter structures using PCR, restriction enzyme analysis, and polyacrylamide gel electrophoresis, and have applied them to the characterization of class 1 integrons in 33 non-typhoidal Salmonella serotypes in Korea. Class 1 integrons were detected in four serotypes: S. Derby (SD), S. Istanbul (SI), S. Paratyphi B (SPB), and S. Livingstone (SL), and the amplicon sizes were 1.0 Kb (SD, SI and SPB) and 2.0 Kb (SL). All of the 1.0 kb amplicons harbored gene cassettes ( aadA1 or aadA2), but the 2.0 kb amplicon harbored three ( dhfrXII-orfF-aadA2) gene cassettes, which conferred streptomycin/spectinomycin ( aadA) and trimethoprim ( dhfr) resistances. Our promoter structure study revealed three types of promoters; strong P1 (SD), weak P1 (SPB and SL), and weak P1 + P2 (SI). In conclusion, the class 1 integrons were detected in Korean NTS, and their promoter structures were found to be variable. Therefore, our methods may prove helpful in terms of our understanding of molecular diversity, as well as the transmission of class 1 integrons and phenotype-genotype relationships in antibiotic-resistance.

Characterization of antimicrobial resistance and class 1 and 2 integrons in Salmonella enterica isolates from different sources in Portugal

The antimicrobial resistance profiles of 1183 Salmonella isolates collected during 2002-2003 from several sources (human, food products and environment) were evaluated. The occurrence, distribution and cassette content of class 1 and 2 integrons among the sulphonamide-resistant population, as well as the role of particular clones to the spread of these genetic elements, were investigated. The isolates were examined for susceptibility to antimicrobial agents. The characterization of class 1 and 2 integrons was investigated using PCR, PCR-RFLP (restriction fragment length polymorphism) and sequencing in the sulphonamide-resistant isolates. Conjugation assays and clonality analysis by PFGE were performed. The most common resistance phenotypes were to nalidixic acid, tetracycline, streptomycin, sulfamethoxazole and ampicillin (ranging from 31% to 17%). Resistance to sulphonamides (n=200) was associated with resistance to other antimicrobial agents, with 75% of the isolates carrying one or two class 1 integrons while only 3% simultaneously carried class 1 and 2 integrons. Integrons were observed among at least 11 serotypes (mainly Typhimurium) and in a reduced number of PFGE clones (20). Eight class 1 integron types were found, with the aadA genes (aadA1, aadA2 and aadA5) alone or downstream of a trimethoprim (dfrA1, dfrA12 and dfrA17) or a beta-lactamase resistance gene (blaoxa-30) and the blaPSE-1 gene alone. Most of the class 1 integron types were shared by several clones from the same or different serotypes obtained either from humans or food products of animal origin, especially pork products. However, some Typhimurium-specific integrons were found: aadA2 plus blaPSE-1 and blaoxa-30-aadA1. Apart from the hypothetical contribution of the conjugative transfer of integrons, the incidence of Salmonella carrying these genetic units seems to rely on the ability of certain clones to spread or persist in particular animal niches. Our data suggest that food-producing animals might be simultaneously considered as a reservoir of clones and integrons carrying antibiotic resistance genes, thus making the food chain, especially pork products, a possible source of multidrug-resistant isolates in humans.

The role of horizontal gene transfer in the spread of trimethoprim–sulfamethoxazole resistance among uropathogenic Escherichia coli in Europe and Canada

To describe the distribution of trimethoprim-sulfamethoxazole resistance genes and the role of horizontal gene transfer and clonal expansion in recent increases of antibiotic resistance rates among uropathogenic Escherichia coli in Europe and Canada. We identified antibiotic resistance alleles sul1, sul2, sul3 and dfr along with type 1 and type 2 integrons among 350 uropathogenic E. coli isolates from a cross-sectional study of acute, uncomplicated, community-acquired urinary tract infections in 16 western European countries and Canada (ECOSENS). Trimethoprim resistance gene distributions showed no regional dependency (P = 0.84). The most common trimethoprim resistance gene was dfrA1, which occurred in 37.9% of dfr containing isolates. Similarly, the sulfamethoxazole resistance gene distributions did not vary significantly by region (P = 0.20). sul2, the most common sulfamethoxazole resistance gene, was found in 77.9% of sulfamethoxazole-resistant isolates. The distribution of type 1 and type 2 integrons varied slightly by region (P = 0.04) with type 1 integrons being the more common (85.9%). We observed 34 combinations of the sul genes, dfr genes and integron types; the most common combinations were broadly disseminated across every region examined. Horizontal gene transfer plays a larger role than clonal expansion in the increase of trimethoprim-sulfamethoxazole resistance levels in Europe and Canada.

Class 1 Integrons in Enterobacteriaceae Isolated from Clinical Infections of Horses and Dogs in The Netherlands

Integrons in gentamicin- and cotrimoxazole-resistant Enterobacteriaceae from dogs and horses with clinical infections were analyzed by conserved segment PCR-RFLP. Five distinct integron types were found, most of which have previously been reported in Enterobacteriaceae isolated from humans and farm animals, indicating that resistance genes are exchanged between the reservoirs in humans, farm animals, and companion animals.

Integrons inEscherichia colifrom Food-Producing Animals in The Netherlands

The presence and character of class 1 integrons in multidrug-resistant Escherichia coli from slaughter animals and meat was determined by integrase-specific PCR and conserved segment PCR-restriction fragment length polymorphism (RFLP). At least five different class 1 integron types were found and three types were shared between hospitalized patients, humans in the community, meat, and slaughter animals. Common integron types indicate that antibiotic resistance genes are exchanged via the food chain between different reservoirs of both human and animal origin.

Evaluation of genetic determinants involved in β-lactam- and multiresistance in a surgical ICU

Antibiotic resistance is a major and well-known problem in intensive care units (ICUs) world-wide and previously susceptible isolates become resistant through the acquisition of resistance determinants from other bacteria or the development of mutations, as is the case in β-lactam resistance. We evaluated the presence of resistance determinants involved in β-lactam resistance and multi-resistance in order to establish the contribution of horizontal gene transfer to the spread of resistance in a surgical ICU during an antibiotic rotation study. Pseudomonas aeruginosa and Enterobacteriaceae isolates were selected and iso-electric focusing (IEF), DNA-typing methods such as specific β-lactamase and specific integron PCRs were performed to determine the presence of β-lactamases. The PCRs specific for IMP-1, OXA-1, and VIM-type β-lactamases performed on the selected P. aeruginosa and Enterobacteriaceae isolates with MICs for cephalosporins >1 mg/l did not demonstrate any of these β-lactamases. IEF for 14 pseudomonads, representing 7 genotypes from 9 patients, showed a β-lactamase with a p I larger than 8.5 in 13 of the isolates. The integrase PCR was positive for only five isolates from three patients and conserved segment PCR showed integrons of variable sizes (700, 900, 1400 and 1500 bp). Each patient had its own integron types. It can be concluded that integrons and associated resistance determinants played only a minor role in the surgical ICU and β-lactam resistance among P. aeruginosa isolates was most likely due to the derepression of its AmpC gene.

Prevalence of dfr genes associated with integrons and dissemination of dfrA17 among urinary isolates of Escherichia coli in Korea.

The association of trimethoprim-resistant dfr genes with integrons was investigated in urinary Escherichia coli isolates in Korea from the last two decades. Of 623 E. coli isolates from urine specimens, 421 trimethoprim-resistant isolates were studied for dfr genes associated with integrons. Integrase genes were amplified and the PCR products restricted using HinfI to classify integron types. Gene cassette regions for the class 1 and class 2 integrons were amplified and sequenced. PFGE was performed to determine the epidemiological relationship of E. coli isolates. The carriage of class 1 integrons was found to be significantly higher in trimethoprim-resistant isolates (69%) than in trimethoprim-susceptible isolates (19%). Among the trimethoprim-resistant isolates, the frequency of dfr genes associated with class 1 integrons increased sharply from 10% of the isolates during 1980-1985 to 53% during 1996-1997 and to 46% during 2001-2002. Five different dfr cassettes--dfrA1, dfrA5, dfrA7, dfrA12 and dfrA17--were identified among the urinary E. coli isolates from the last two decades; dfrA12 was the most prevalent during 1980-1985 and dfrA17 during 1996-1997 and 2001-2002. The majority of dfr genes associated with class 1 integrons were conjugally transferable to recipient E. coli strains. The E. coli isolates that carried dfrA17 associated with class 1 integrons were found to be phylogenetically unrelated, indicating that dfrA17 was widely distributed in the different clones of E. coli. Class 1 integrons were found to be an important genetic element of resistance to trimethoprim among urinary E. coli in Korea, and the prevalence of dfrA17 was mainly due to the horizontal transfer of class 1 integrons through conjugative plasmids.

Molecular analysis of antibiotic resistance gene clusters in vibrio cholerae O139 and O1 SXT constins.

Many recent Asian clinical Vibrio cholerae E1 Tor O1 and O139 isolates are resistant to the antibiotics sulfamethoxazole (Su), trimethoprim (Tm), chloramphenicol (Cm), and streptomycin (Sm). The corresponding resistance genes are located on large conjugative elements (SXT constins) that are integrated into prfC on the V. cholerae chromosome. We determined the DNA sequences of the antibiotic resistance genes in the SXT constin in MO10, an O139 isolate. In SXT(MO10), these genes are clustered within a composite transposon-like structure found near the element's 5' end. The genes conferring resistance to Cm (floR), Su (sulII), and Sm (strA and strB) correspond to previously described genes, whereas the gene conferring resistance to Tm, designated dfr18, is novel. In some other O139 isolates the antibiotic resistance gene cluster was found to be deleted from the SXT-related constin. The El Tor O1 SXT constin, SXT(ET), does not contain the same resistance genes as SXT(MO10). In this constin, the Tm resistance determinant was located nearly 70 kbp away from the other resistance genes and found in a novel type of integron that constitutes a fourth class of resistance integrons. These studies indicate that there is considerable flux in the antibiotic resistance genes found in the SXT family of constins and point to a model for the evolution of these related mobile elements.

Rapid Emergence of Ciprofloxacin-Resistant Enterobacteriaceae Containing Multiple Gentamicin Resistance-Associated Integrons, the Netherlands

Abstract In a hematology unit in the Netherlands, the incidence of ciprofloxacin-resistant Enterobacter cloacae and Escherichia coli increased from <0.5% to 20.7% and <0.5% to 64%, respectively, from 1996 to 1999. Clonal spread of single genotypes of both ciprofloxacin-resistant E. coli and Enterobacter cloacae from patient to patient was documented by pulsed-field gel electrophoresis and random amplification of polymorphic DNA. In addition, genetically heterogeneous strains were isolated regularly. Integrons associated with gentamicin resistance were detected in Enterobacter cloacae and E. coli strains. Integron-containing E. coli were detected in all hematology wards. In contrast, in Enterobacter cloacae strains two integron types were encountered only in the isolates from one ward. Although in all patients identical antibiotic regimens were used for selective decontamination, we documented clear differences with respect to the nosocomial emergence of ciprofloxacin-resistant bacterial strains and gentamicin resistance-associated integrons.

Rapid emergence of ciprofloxacin-resistant enterobacteriaceae containing multiple gentamicin resistance-associated integrons in a Dutch hospital.

In a hematology unit in the Netherlands, the incidence of ciprofloxacin-resistant Enterobacter cloacae and Escherichia coli increased from from 1996 to 1999. Clonal spread of single genotypes of both ciprofloxacin-resistant E. coli and Enterobacter cloacae from patient to patient was documented by pulsed-field gel electrophoresis and random amplification of polymorphic DNA. In addition, genetically heterogeneous strains were isolated regularly. Integrons associated with gentamicin resistance were detected in Enterobacter cloacae and E. coli strains. Integron-containing E. coli were detected in all hematology wards. In contrast, in Enterobacter cloacae strains two integron types were encountered only in the isolates from one ward. Although in all patients identical antibiotic regimens were used for selective decontamination, we documented clear differences with respect to the nosocomial emergence of ciprofloxacin-resistant bacterial strains and gentamicin resistance-associated integrons.