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PubMed2005

Detection and typing of integrons in epidemic strains of Acinetobacter baumannii found in the United Kingdom.

Integrons were sought in Acinetobacter isolates from hospitals in the United Kingdom by integrase gene PCR. Isolates were compared by pulsed-field gel electrophoresis, and most belonged to a small number of outbreak strains or clones of A. baumannii, which are highly successful in the United Kingdom. Class 1 integrons were found in all of the outbreak isolates but in none of the sporadic isolates. No class 2 integrons were found. Three integrons were identified among the main outbreak strains and clones. While a particular integron was usually associated with a strain or clone, some members carried a different integron. Some integrons were associated with more than one strain. The cassette arrays of two of the integrons were very similar, both containing gene aacC1, which confers resistance to gentamicin, two open reading frames coding for unknown products (orfX, orfX'), and gene aadA1a, which confers resistance to spectinomycin and streptomycin. The larger of these integrons had two copies of the first (orfX) of the gene cassettes coding for unknown products. The third integron, with a cassette array containing gene aacA4, which codes for amikacin, netilmicin, and tobramycin resistance; a chloramphenicol acetyltransferase, catB8; and gene aadA1, conferring resistance to spectinomycin and streptomycin, was associated with an OXA-23 carbapenemase-producing clone, which has spread rapidly in hospitals in the United Kingdom during 2003 and 2004. These integron cassette arrays have been found in other outbreak strains of A. baumannii from other countries. We conclude that integrons are useful markers for epidemic strains of A. baumannii and that integron typing provides valuable information for epidemiological studies.

Acinetobacter Infections↗
PubMed1999

Class 1 integrons, gene cassettes, mobility, and epidemiology.

Integrons are genetic elements that, although unable to move themselves, contain gene cassettes that can be mobilized to other integrons or to secondary sites in the bacterial genome. The majority of approximately 60 known gene cassettes encode resistance to antibiotics. Recently, a number of gene cassettes encoding extended-spectrum beta-lactamases or carbapenemases have been described. Up to at least five cassettes may be present in an integron, which leads to multiresistance. Frequently, more than one integron is observed within the same bacterial cell. Integrons are widespread in their species distribution. Although integrons are normally reported from Enterobacteriaceae and other gram-negative bacteria, an integron has been described in Corynebacterium glutamicum, a gram-positive species. The gene cassette in this integron showed even higher expression when compared to the expression in Escherichia coli. Integrons have been reported from all continents and are found frequently. The widespread occurrence of integrons is thought to be due to their association with transposon plasmids, conjugative plasmids, or both. Integrons form an important source for the spread of antibiotic resistance, at least in gram-negative bacteria but also potentially in gram-positive bacteria. The aim of this review is to describe the versatility of integrons, especially their mobility and their ability to collect resistance genes.

Animals↗
PubMed1999

Identification and characterization of class 1 integrons in bacteria from an aquatic environment.

In a survey of 3000 Gram-negative bacteria isolated from an estuarine environment over a 2 month period, the incidence of class 1 integrons was determined to be 3.6%. Of 85 integrons studied further, 11 lacked both the qacEdelta1 and sull genes usually present in the 3' conserved segment of the integron. The qacEdelta1 and sull genes were identified in the 3' conserved segment of 36 integrons. The remaining 38 integrons lacked a sull gene but contained a qacE gene. The variable region of 74 integrons was characterized by PCR and sequence analysis. Forty of the integrons were found to lack integrated gene cassettes, although 21 of these 'empty' integrons were shown to contain inserted DNA which has been tentatively identified as a novel insertion sequence (IS) element. Of the 34 integrons which contained inserted gene cassettes, the aadA1a gene was found to be the most prevalent (74%). Nineteen integrons contained additional or other gene cassettes in their variable region, including those encoding resistance to trimethoprim (dfr1a, dfrIIc, dfrV, dfrVII, dfrXII), chloramphenicol (catB3, catB5), aminoglycosides (aadA2, aacA4, aacC1), beta-lactamases (oxa2) and erythromycin (ereA). This study confirms the occurrence of integrons in bacteria from a natural habitat and suggests that in the absence of continued antibiotic selective pressures, integrons which persist appear to preferentially exist without integrated antibiotic resistance gene cassettes.

Anti-Bacterial Agents↗
PubMed1999

Detection of integrons in worldwide nosocomial isolates of Acinetobacter spp.

OBJECTIVE: To examine the distribution of integrons in genotypically unrelated worldwide multiresistant clinical isolates of Acinetobacter spp. METHODS: The presence and genetic location of class 1, 2 and 3 integrons were examined in a genotypically heterogeneous collection of 25 nosocomial isolates of Acinetobacter spp., from 15 locations in 11 different countries worldwide, by hybridization and PCR-based methods. Class 1 integron structures were characterized genetically by a PCR mapping technique. RESULTS: Class 1 integrons were detected in 17 of the 25 Acinetobacter isolates examined. Only one isolate contained a class 2 integron. No class 3 integrons were detected. The integrons varied in size and in the number of inserted cassettes, but similar integrons were found in genotypically distinct isolates from different locations worldwide. These structures were integrated into the chromosome in all isolates where they were detected, although some integrons were capable of subsequent transfer or mobilization. Genes coding for aminoglycoside-modifying enzymes formed the predominant cassettes identified within the integrons. CONCLUSIONS: Clinical isolates of Acinetobacter spp. from diverse locations seem to share resistance mechanisms acquired from other genera by a variety of mechanisms, including dissemination of integrons. Once integrons are incorporated into the bacterial genome, Acinetobacter spp. are potentially able to act as a reservoir of resistance genes for other species and genera.

Journal Article↗
PubMed2005

Prevalence and characterization of class 1 and class 2 integrons in Escherichia coli isolated from meat and meat products of Norwegian origin.

OBJECTIVES: The aim of the study was to investigate the prevalence of integrons and to characterize inserted gene cassettes in Escherichia coli isolated from meat and meat products of Norwegian origin. METHODS: The strains investigated (n = 241 resistant out of 944 investigated) were collected within the frame of the Norwegian monitoring programme for antimicrobial resistance in bacteria from feed, food and animals (NORM-VET) during the years 2000-2003. PCR and DNA sequencing were used for detection of the integrase genes and gene cassettes within the integrons. RESULTS: Integrons were detected in 43 (18%) of the 241 resistant isolates. Class 1 integrons were detected in 29 (12%) strains and class 2 integrons were detected in 14 (6%) strains. Ten different gene cassettes were detected: dfrA1, dfr2a, dfrA12, aadA1, aadA2, catB2, oxa-30, sat, sat1 and orfF. The dfrA1 + aadA1 combination was the most prevalent cassette combination, detected in 12 of 29 class 1 integrons. Twelve (of 14) class 2 integrons contained a cassette area consistent with that on Tn7, the remaining two contained the cassettes sat + sat1 + aadA1. Nearly one-third of the class 1 integrons (9 of 29) lacked the sul1 gene. Ten gene cassettes (one dfr2a, two catB2 and seven aadA1) were expressed at levels below breakpoint values normally used to classify strains as resistant. CONCLUSIONS: Integrons of class 1 or 2 were present in approximately 18% of the resistant E. coli strains investigated. Certain cassette combinations in class 1 integrons seem to be more widespread than others, like the dfrA1 + aadA1. Low-level expression of antimicrobial resistance, caused by the expression of certain gene cassettes in some integrons represents an obstacle in classifying strains as susceptible or resistant.

DNA Transposable Elements↗
PubMed2006

Molecular characteristics of class 1 and class 2 integrons and their relationships to antibiotic resistance in clinical isolates of Shigella sonnei and Shigella flexneri.

OBJECTIVES: To analyse the gene cassettes and determine the roles of class 1 and class 2 integrons in antibiotic-resistant strains of Shigella sonnei (n=31) and Shigella flexneri (n=33). METHODS: Various molecular techniques, including PCR and Southern-blotting analysis, were used to analyse various markers of class 1 and class 2 integrons in these 64 S. sonnei and S. flexneri isolates collected in Hangzhou, China. The gene cassette arrays in integrons were identified by DNA sequencing and/or restriction fragment length polymorphism. Two genomic DNA fragments, one containing intI1 from a S. flexneri isolate that contains intI1 but lacks 3'-conserved region and another containing intI2 from a S. sonnei isolate, were cloned into pUC19 vectors and sequenced. The links between integron gene cassette arrays and antibiotic resistance were analysed. RESULTS: Class 2 integrons were present in 80.6% (25/31) of the S. sonnei isolates and 87.9% (29/33) of the S. flexneri isolates. All of these integron 2-positive isolates contained constant gene cassette arrays of dfrA1+sat1+aadA1 which confer resistance to trimethoprim and streptomycin. It was demonstrated that the class 2 integron was located in the Tn7 region inside the attTn7 locus downstream of glmS in Shigella. Class 1 integrons were found in 9.4% (6/64) of Shigella spp. isolates. An atypical class 1 integron without a 3'-conserved segment on the Shigella chromosome, termed Shigella atypical class 1 integron (SAI), was present in 84.9% (28/33) of S. flexneri isolates. The SAI contained two gene cassettes, bla(OXA30) and aadA1; however, the SAI conferred resistance to ampicillin, but not to streptomycin, in Escherichia coli host. The bla(OXA30) and aadA1 cassettes of the SAI seemed to be always coordinately excised or integrated. CONCLUSIONS: Multiple and complex mechanisms involving mobile genetic elements in class 1 and class 2 integrons and antibiotic resistance have been developed in the evolution of Shigella strains.

Ampicillin Resistance↗
PubMed2005

Integrons and gene cassettes in clinical isolates of co-trimoxazole-resistant Gram-negative bacteria.

Despite a trend of declining consumption, resistance to co-trimoxazole has increased during a 12-year period in Stockholm. The molecular background to this surprising development was investigated by using PCR to screen for integrons and specific resistance genes, followed by sequence analysis of selected integrons, in 105 clinical urinary isolates of Gram-negative bacteria selected partly for trimethoprim resistance. Sixty-five integrons of class 1 or 2 were detected in a subset of 59 isolates, and of these positive isolates, all but one were resistant to trimethoprim. However, 11 isolates were resistant to trimethoprim, but negative for integrons. Isolates positive for integrons were resistant to an average of 4.2 antibiotics, compared with 1.9 antibiotics for integron-negative isolates. Despite this, the only gene cassettes identified in 19 class 1 integrons analysed were dfr and aadA cassettes. Thus, only resistance to trimethoprim, streptomycin, spectinomycin and sulphonamides could be explained by the presence of integrons in these isolates. A new dfr gene, named dfrA22, was discovered as a single gene cassette in a class 1 integron. In addition, sulphonamide resistance in many isolates was caused by carriage of sul2, which has no known association with integrons. Resistance to co-trimoxazole and many other antibiotics was thus not accounted for fully by the presence of integrons in these isolates.

Base Sequence↗
PubMed2003

Recombination activity of a distinctive integron-gene cassette system associated with Pseudomonas stutzeri populations in soil.

Class 1 integrons have strongly influenced the evolution of multiple antibiotic resistance. Diverse integrons have recently been detected directly in a range of natural environments. In order to characterize the properties of these environmental integrons, we sought to isolate organisms containing integrons from soils, which resulted in the isolation of Pseudomonas stutzeri strain Q. Further isolation efforts targeted at this species resulted in recovery of two other strains (P and BAM). 16S rRNA sequences and chromosome mapping showed that these three strains are very closely related clonal variants in a single genomovar of P. stutzeri. Only strains Q and BAM were found to contain an integron and an associated gene cassette array. The intI and attI components of these strains showed 99 and 90% identity, respectively. The structure of these integrons and their associated gene cassettes was similar to that reported previously for other integron classes. The two integrons contained nonoverlapping sets of cassette-associated genes. In contrast, many of the cassette-associated recombination sites in the two integrons were similar and were considered to constitute a distinct subfamily consisting of 59-base element (59-be) recombination sites (the Pseudomonas subfamily). The recombination activity of P. stutzeri integron components was tested in cointegrate assays. IntIPstQ was shown to catalyze site-specific recombination between its cognate attI site and 59-be sites from antibiotic resistance gene cassettes. While IntIPstQ did not efficiently mediate recombination between members of the Pseudomonas 59-be subfamily and other 59-be types, the former sites were functional when they were tested with IntI1. We concluded that integrons present in P. stutzeri possess recombination activity and represent a hot spot for genomic diversity in this species.

Amino Acid Sequence↗
PubMed2002

Characterization of the class 3 integron and the site-specific recombination system it determines.

Integrons capture gene cassettes by using a site-specific recombination mechanism. As only one class of integron and integron-determined site-specific recombination system has been studied in detail, the properties of a second class, the only known class 3 integron, were examined. The configuration of the three potentially definitive features of integrons, the intI3 gene, the adjacent attI3 recombination site, and the P(c) promoter that directs transcription of the cassettes, was similar to that found in the corresponding region (5' conserved segment) of class 1 integrons. The integron features are flanked by a copy of the terminal inverted repeat, IRi, from class 1 integrons on one side and a resolvase-encoding tniR gene on the other, suggesting that they are part of a transposable element related to Tn402 but with the integron module in the opposite orientation. The IntI3 integrase was active and able to recognize and recombine both known types of IntI-specific recombination sites, the attI3 site in the integron, and different cassette-associated 59-be (59-base element) sites. Both integration of circularized cassettes into the attI3 site and excision of integrated cassettes were also catalyzed by IntI3. The attI3 site was localized to a short region adjacent to the intI3 gene. Recombination between a 59-be and secondary sites was also catalyzed by IntI3, but at frequencies significantly lower than observed with IntI1, the class 1 integron integrase.

Attachment Sites, Microbiological↗
PubMed2004

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

OBJECTIVES: The association of trimethoprim-resistant dfr genes with integrons was investigated in urinary Escherichia coli isolates in Korea from the last two decades. METHODS: 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. RESULTS: 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. CONCLUSION: 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.

Anti-Infective Agents, Urinary↗
PubMed2006

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

OBJECTIVES: 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. METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.

Anti-Bacterial Agents↗
PubMed2006

Occurrence of integrons and antimicrobial resistance genes among Salmonella enterica from Brazil.

OBJECTIVES: To determine the occurrence of antimicrobial resistance genes and role of integrons among 135 antimicrobial-resistant Salmonella enterica from Brazil. METHODS: The presence of antimicrobial resistance genes, class 1 and 2 integrons and gene cassettes was analysed by PCR and sequencing. The genetic location of class 1 integrons was determined in 25 isolates by hybridization and plasmid transfer experiments. RESULTS: Fifty-five of the isolates were positive for class 1 integrons. Integron-positive isolates represented 17 different serovars and were mainly from human (n=28) and animal (n=13) sources. The gene cassette arrangements could be determined in 51 of the positive isolates, which harboured one [dfrA22, aadA1 or orf3 (putative trimethoprim resistance)], two [aadA1-dfrA1, aac(6')-Ib-orf1 (unknown function) or aacA4-aadA1], three [dfrA15b-cmlA4-aadA2, orf2 (unknown function)-dfrA5-orfD] or four [orf4-aacA4-blaOXA-30 (interrupted by an IS1 element)-aadA1] cassettes in their variable region. Only one isolate harboured a class 2 integron with the gene cassette array dfrA1-sat-aadA1. Several integron unrelated resistance genes were also detected in the isolates. Sulphonamide resistance was primarily mediated by sul2 and sul3, tetracycline resistance by tet(B) and tet(A), chloramphenicol resistance by catA1, streptomycin resistance by strA and ampicillin resistance by blaTEM. blaCTX and blaCMY-2 were found in cephalosporin-resistant isolates. Mating and hybridization experiments demonstrated that a high-molecular-weight plasmid mediated the gene transfer of integrons and additional resistance determinants. CONCLUSIONS: The present study revealed that integron-mediated resistance genes contributed to the multiresistance phenotype observed in the isolates, but most resistance genes were located outside the integron structure, as independent genes. However, they might be located on the same conjugative plasmid.

Animals↗
PubMed2006

Class 1 and class 2 integrons in non-prevalent serovars of Salmonella enterica: structure and association with transposons and plasmids.

OBJECTIVES: To characterize class 1 and class 2 integrons which were simultaneously detected in non-typhoid Salmonella enterica strains of non-prevalent serovars, and to investigate their possible association with transposons and/or plasmids. METHODS: Eight multidrug-resistant S. enterica strains belonging to serovars Virchow (4), Panama (2), Grumpensis (1) and Worthington (1), each containing a class 1 and a class 2 integron, were analysed. Nested PCR amplification was used to determine the gene-cassette configuration of the integrons. Overlapping PCR amplifications were applied in integron-transposon linkage experiments. Conjugation and hybridization experiments were used to localize integrons and transposons in the bacterial genome (plasmid and chromosome associated). RESULTS: One of two different class 1 integrons (with variable regions of 1000 bp/aadA1 and 2300 bp/sat-smr-aadA1) inserted into Tn21-like transposons, were found to coexist with the class 2 integron (2300 bp/dfrA1-sat1-aadA1) of Tn7 in the analysed strains. Class 1 integrons were always found in large conjugative plasmids whereas apparently intact or defective copies of the Tn7 integron could be located on the same plasmid and/or the bacterial chromosome. CONCLUSIONS: This report describes different associations between mobile genetic elements that play a crucial role in the capture and spread of antimicrobial drug resistance. As far as we are aware, this is the first description of class 2 integrons in serovars Panama, Grumpensis and Worthington.

Chromosomes, Bacterial↗
PubMed2006

Diverse class 2 integrons in bacteria from beef cattle sources.

OBJECTIVES: The purpose of this study was to determine the diversity of class 2 integrons in bacteria isolated from beef cattle sources. METHODS: The variable regions of a subset of 11 class 2 integron-containing bacteria were analysed by PCR and DNA sequencing for the presence of novel rearrangements. RESULTS: A total of six different class 2 integron arrays were identified and four of these were fully characterized. Three of the four arrays characterized have been previously described; however the remaining array is unlike previously described class 2 integrons. The novel class 2 integron was found in Providencia stuartii and contains an apparently functional class 2 integrase. Examination of the variable region of the P. stuartii integron identified nine open reading frames, mostly of unknown function, and represents the first report of a class 2 integron without inserted antibiotic resistance gene cassettes. CONCLUSIONS: This study has identified a novel class 2 integron found in P. stuartii that contains an apparently functional naturally occurring class 2 integrase. Further investigation of this novel class 2 integron is required to determine the impact of a functional class 2 integrase upon the evolution of class 2 integrons.

Animals↗
PubMed2004

Integrons and multidrug resistance among Escherichia coli causing community-acquired urinary tract infection in southern India.

Antimicrobial resistance genes are often clustered in integrons, genetic elements capable of recombination. There is a paucity of data on the prevalence and role of integrons from community-acquired infections in developing countries where resistance to co-trimoxazole is high. We determined the prevalence of integrons among Escherichia coli causing community-acquired urinary tract infection (UTI). Consecutive isolates of E. coli obtained from UTI of pregnant women at the Christian Medical College Hospital, Vellore, India, during 2002 were included. All isolates were tested for susceptibility to 16 antimicrobials using the disc diffusion method and for integrons of classes 1 and 2 by PCR. Of the 58 isolates tested, 28 (48.3%) were resistant to co-trimoxazole and trimethoprim. All these isolates carried integrons. Three additional isolates were sulfonamide resistant but integron negative. Class 1 integrons were present in 21 (36.2%) isolates. Resistance to ampicillin (p=0.000), nalidixic acid (p=0.001), chloramphenicol (p=0.02), tetracycline (p=0.004) and gentamicin (p=0.02) was significantly more common in isolates with integrons. DNA sequencing of two isolates with integrons showed the presence of aadA, dfr1 and dfr7 genes. This study demonstrated that integrons are widely prevalent in India and that they might play a role in multidrug resistance in E. coli from community-acquired UTI.

Community-Acquired Infections↗
PubMed2005

[Relationship between antibiotic resistance and integrons of Escherichia coli isolated from food].

OBJECTIVE: To investigate the relationship between antibiotic resistance of Escherichia coli strains isolated from food and the integrons they harbored. METHODS: PCRs amplifying intI gene and the variable region between the conserved segments (CS-PCR) were performed for class1, class2, and class 3 integron. And the integron content of every isolate was characterized by RFLP analysis and sequencing. RESULTS: 19 of 50 isolates were identified as being positive for integrase 1 gene in the genomic DNA, of which 13 had detectable amplification products for CS-PCR. Two E. coli isolates had class 2 integron. All the integron-positive strains were resistance to at least 4 antibiotics. Most of the gene cassettes integrated in the integrons conferred resistance against trimethoprim and streptomycin-spectinomycin, and the integrons with the dfr17-aadA5 gene cassettes combination were predominant. Some strains with different antibiotic resistance profile or plasmid profile were found to have the same integron. CONCLUSION: There was a good correlation between Integron-carrying and the antibiotic resistance of Escherichia coli strains isolated from food, but in terms of an individual strain, its antibiotic profile was not consistent with the gene cassettes of the integron it harbored.

Animals↗
PubMed1999

Characterization of integrons in Escherichia coli of the normal intestinal flora of swine.

Multiresistant Escherichia coli isolates of the normal intestinal flora of healthy fattening pigs were examined for the presence of integron class 1 by XL (extra long) PCR. The class 1 integron was detected in 17 isolates originating from 14 healthy animals on seven different farms. One isolate contained two class 1 integrons. The inserted gene cassettes were characterized by DNA sequencing and PCR. The ant(3")-Ia gene responsible for resistance to streptomycin/spectinomycin was inserted in all integrons detected. Fifteen isolates contained this gene cassette as the only inserted cassette. Three isolates contained integrons with two gene cassettes. Two isolates contained integrons with the trimethoprim resistance gene dfr1 and one isolate contained the oxa1 beta-lactamase gene upstream to the ant(3")-Ia gene. Detection of these three different resistance gene cassettes in bacteria from swine shows that cassettes occurring in integrons in human clinical isolates also appear in bacteria of the normal intestinal flora of healthy swine. Two integron-harboring strains were obtained from each of three different animals. These strains were probably not clonal derivatives of each other, suggesting the existence of different multiresistance clones within the intestinal normal flora of one specific animal. The oxa1 nucleotide sequence found in E. coli from swine differ by seven nucleotides from the oxa1 nucleotide sequence of the gene from the R-plasmid RGN238. The fact that these two sequences are not identical might indicate that the two genes have evolved separately in different surroundings from the common ancestor. Transmissible plasmids of approximately 200 kb containing integron class I were detected in eight of the isolates when conjugation experiments were performed with E. coli DH5 as recipient strain. The transfer frequency ranged from 4x10(-4) to 6x10(-2) transconjugants per recipient cell. This study shows that the enteric commensals of domestic animals may be considered as a reservoir of integron-containing transmissible plasmids and gene cassettes that might be transferable to the pathogens of swine and to important zoonotic bacteria associated with the enteric flora of swine such as Salmonella typhimurium DT104.

Animals↗
PubMed1998

Class I integrons in Gram-negative isolates from different European hospitals and association with decreased susceptibility to multiple antibiotic compounds.

Class I integrons are associated with carriage of genes encoding resistance to antibiotics. Expression of inserted resistance genes within these structures can be poor and, as such, the clinical relevance in terms of the effect of integron carriage on susceptibility has not been investigated. Of 163 unrelated Gram-negative isolates randomly selected from the intensive care and surgical units of 14 different hospitals in nine European countries, 43.0% (70/163) of isolates were shown to be integron-positive, with inserted gene cassettes of various sizes. Integrons were detected in isolates from all hospitals with no particular geographical variations. Integron-positive isolates were statistically more likely to be resistant to aminoglycoside, quinolone and beta8-lactam compounds, including third-generation cephalosporins and monobactams, than integron-negative isolates. Integron-positive isolates were also more likely to be multi-resistant than integron-negative isolates. This association implicates integrons in multi-drug resistance either directly through carriage of specific resistance genes, or indirectly by virtue of linkage to other resistance determinants such as extended-spectrum beta-lactamase genes. As such their widespread presence is a cause for concern. There was no association between the presence of integrons and susceptibility to cefepime, amikacin and the carbapenems, to which at least 97% of isolates were fully susceptible.

Anti-Bacterial Agents↗