The sul3 gene has recently been found in pathogenic E. The mechanisms of quinolone resistance had been previously analyzed in these 17 strains 7 , Previous Section Next Section Integron analysis. Class 1 and class 2 integrons, the most frequently found in resistant bacteria 14 , 23 , 31 , 32 , were analyzed in all our strains. Twelve strains presented the intI1 gene and four presented the intI2 gene; one of these was E. The VR of the class 1 integron was analyzed in the 12 intI1-positive strains, and the following gene cassette arrangements were detected Table 3: Thus, Co was studied in detail by PCR mapping.
Sequencing revealed the presence of the dfrA12 plus orfF plus aadA2 gene cassettes Table 3. As in the case of our results, most class 1 integrons published are composed of two or more gene cassettes 12 , 22 , 40 , Analysis of class 1 and class 2 integrons and their resistance gene cassettes in the 17 multiresistant E.
The dfrA1 gene cassette detected in Co presented the AsnAsp amino acid change, corresponding to the sequence of the dfrA1-like gene found in this strain Table 3. Previous Section Next Section Analysis of the mar locus. Another mechanism contributing to a multiple-antibiotic-resistant phenotype is associated with mar locus regulation 1 , 2 , 5. Amino acid changes in MarR and the nucleotide mutations in the operator-promoter region marO were studied for all strains by PCR, sequencing, and comparison with the GenBank sequence found under accession number M and corresponding to the mar regulon Table 4.
Fifteen strains showed GlySer and TyrHis substitutions in MarR, which had been found also in resistant clinical strains Note that position is inside the conserved region between amino acids 92 and in MarR and may be important for binding with the region corresponding to marO 1.
However, other authors have considered that these substitutions could correspond to genotypic variations in marR without loss of repressor activity Another amino acid change in MarR, Leu36Gln, was found in only one strain in our study; this is the first time that this substitution has been reported. Further studies are necessary to relate this substitution to antibiotic resistance. Analysis of amino acid changes in MarR protein and nucleotide mutations in marO region of 17 multiresistant E.
Similarly a year — follow-up study on E. Although studies of farms have shown an association of multidrug-resistant E. Recent data are available in several countries that established resistance monitoring programs during the mids. The resistance trend in chickens observed during this period varied on the basis of the antimicrobial agents. For example, resistance during — decreased slightly for kanamycin Cefoxitin resistance increased from 7. To better understand the historical emergence of resistance since the advent of the antimicrobial drug age, which led to baseline data in the first year of NARMS testing, we assayed E.
This information, when coupled with secular surveillance data, will provide a broader picture of evolution of resistance and lay the groundwork for understanding genetic mechanisms of resistance development and dissemination.
These isolates were recovered from human and animal specimens e. For human isolates obtained from CDC, most acquired during through the late s were maintained on trypticase soy agar stabs sealed with paraffin and stored at room temperature. Three hundred twenty-three Fifty percent were from 10 states: Distribution of isolates by source and year are shown in Table 1.
Results were interpreted according to National Committee for Clinical and Laboratory Standards criteria 16 where available Table 2. Statistical Analysis The Mann-Kendall test, a nonparametric statistical test, was performed to detect a monotone increasing or decreasing resistance trend over time. Magnitude of annual change was estimated by using a slope parameter, Q, and the Sen nonparametric method Results Antimicrobial Drug Susceptibility Overall, As expected, the most common resistance phenotypes were to older drugs such as tetracycline When analyzed by source, E.
Among human isolates, resistance was observed most often to sulfonamide Of isolates recovered from animal sources, Figure 1 Figure 1. Change in antimicrobial drug resistance patterns among Escherichia coli isolates, United States, — Figure 2 Figure 2.
Distribution of multidrug resistance patterns among Escherichia coli isolates recovered from different sources, United States, — Antimicrobial drug resistance was observed for drugs tested at different frequencies Table 2.
The proportion of pan-susceptible E. Conversely, multidrug resistance increased from 7. Five hundred seventy A larger proportion of multidrug-resistant isolates was recovered from animals than humans Figure 2.
One hundred ninety-one Two strains showed resistance to all 15 drugs tested; both strains were recovered from cattle in Concurrent resistance to tetracycline and streptomycin was the most common co-resistance phenotype A total of Trend analysis of selected antimicrobial agents among Escherichia coli isolates from humans A and animals B , United States, — The major goal of this study was to document antimicrobial drug resistance among historical bacteria from humans and animals to associate emergence of resistance with approval of new antimicrobial classes.
The resistance rate to ampicillin in animal E. In contrast, resistance rates for sulfonamide and tetracycline among animal E. There was a linear increasing trend in resistance to ampicillin 0. Cephalothin resistance significantly increased over time 0. In our study isolates, gentamicin resistance was observed in the s among animal E. Ceftiofur-resistant and ceftriaxone-resistant strains were not detected until — among human and animal E.
None of the human E. Discussion To help characterize evolution of drug resistance in E. We tested 1, E. Resistance to sulfonamide was one of the most common resistance profiles identified among our study isolates and showed a monotone increasing resistance trend over time. Sulfonamide resistance has been observed in human E. These drugs were administered alone from the s through the s in humans and were almost exclusively combined with diaminopyrimidines e.
In animal production systems, SUL is one of the most commonly used drugs as a single agent or in combination with diaminopyrimidines e. A high prevalence of clinical resistance to sulfonamides was reported in enteric bacteria isolated from healthy food animals and humans 10 , 22 , 23 and is often associated with acquisition of the resistance genes sul1 and sul2 Sulfonamide resistance genes are commonly associated with mobile genetic elements, and these elements play a major role in dissemination of multiple antimicrobial drug resistance genes in E.
In addition, despite a major reduction in the rate of sulfonamide use in the United Kingdom in , resistance to sulfonamides persisted at high rates among clinical E.
Similarly, a year — follow-up study on antimicrobial drug resistance at the Karolinska Hospital in Stockholm, Sweden, reported an increase in sulfonamide resistance despite decreased use Linkage of sulfonamide resistance genes, particularly as a constituent of class I integrons, to determinants conferring resistance to antimicrobial drugs that are still commonly used might help explain persistence of sulfonamide resistance In addition to co-selection by drugs still commonly used, Enne et al.
Tetracycline resistance was the most common type of resistance observed and the most prevalent resistance phenotype in animal isolates This finding is not surprising because tetracycline has been widely used in therapy and to promote feed efficiency in animal production systems since its approval in 2 , Persistence of tetracycline resistance was reported in animal coliforms a decade after it was no longer used in feed or for treatment We commonly found co-resistance for tetracycline with streptomycin, sulfonamide, ampicillin, and chloramphenicol, as in other studies 23 , 30 , A small percentage of E.
Chloramphenicol is not approved for use in food animals in the United States. Persistence of chloramphenicol resistance in E. Florfenicol, a closely related drug, was approved for treatment of respiratory diseases in cattle in the United States in Florfenicol resistance mediated by the flo gene confers nonenzymatic cross-resistance to chloramphenicol 33 , 34 and might select for nascent resistance in recent strains.
Of known chloramphenicol-resistance genes, only a small number mediate resistance to florfenicol For example, chloramphenicol-resistant strains in which resistance is exclusively based on activity of chloramphenicol acetyltransferases do not show resistance to florfenicol Of chloramphenicol-resistant animal E. In addition, our data showed not only persistence of chloramphenicol but an increasing tetracycline and SUL resistance trend over time among animal E.
These observations could be explained by co-selection of mobile resistance elements or by unknown substrate s for the chloramphenicol-resistance determinants that serve as a selection pressure 23 , Gentamicin was approved for use in 2. Although gentamicin resistance was rare in human E.
Since , resistance to gentamicin has increased among animal E. The overall rate of gentamicin resistance was slightly higher in chicken Gentamicin is widely used in the poultry industry. Aminoglycosides approved for use in food animals in the United States include dihydostreptomycin, efrotomycin, hygromycin B, neomycin, spectinomycin, streptomycin, and apramycin
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