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At least 811 records · Page 45Linked to original sources
PubMed2006

Characterization of antimicrobial resistance of Salmonella Newport isolated from animals, the environment, and animal food products in Canada.

Multi-drug-resistant (MDR) Salmonella enterica serovar Newport strains are increasingly isolated from animals and food products of animal origin and have caused septicemic illness in animals and humans. The purpose of this study was to determine the occurrence and the epidemiologic, phenotypic, and genotypic characteristics of S. Newport of animal origin that may infect humans, either via the food chain or directly. During the 1993-2002 period, the Office International des Epizooties Reference Laboratory for Salmonellosis in Guelph, Ontario, received 36 841 Salmonella strains for serotyping that had been isolated from animals, environmental sources, and food of animal origin in Canada. Of these, 119 (0.3%) were S. Newport. Before 2000, none of 49 S. Newport strains was resistant to more than 3 antimicrobials. In contrast, between January 2000 and December 2002, 35 of 70 isolates, primarily of bovine origin, were resistant to at least 11 antimicrobials, including the extended-spectrum cephalosporins. The blaCMY-2', flo(st'), strA, strB, sulII, and tetA resistance genes were located on plasmids of 80 to 90 MDa that were self-transmissible in 25% of the strains. Conserved segments of the integron 1 gene were found on the large MDR-encoding plasmids in 3 of 35 strains additionally resistant to gentamicin and spectinomycin or to spectinomycin, sulfamethoxazole-trimethoprim, and trimethoprim. Resistance to kanamycin and neomycin was encoded by the aphA-1 gene, located on small plasmids (2.3 to 6 MDa). The increase in bovine-associated MDR S. Newport infections is cause for concern since it indicates an increased risk of human acquisition of the infection via the food chain.

Animals↗
PubMed2005

[The effect of silver sulfadiazine on Acinetobacter baumannii strains isolated in burn units].

The genotype structure and silver sulfadiazine (SDS) resistance of a number of Acinetobacter baumanii strains that circulated for a prolonged period of time in burn UCUs were studied. The most resistant strain (SDS MIC 50 mcg/ml) contained a class 1 integron with the gene of sulfonamides resistance (sul1) in its genome. Possible reasons for selection of the multiple resistance among Acinetobacter spp. in burn units are discussed.

Acinetobacter baumannii↗
PubMedDate not supplied

[Prevalence of metallo-beta-lactamase in carbapenem resistant Pseudomonas aeruginosa at a university hospital of Buenos Aires City].

The present study was conducted to estimate the prevalence of metallo-beta-lactamases in 91 consecutive carbapenem resistant Pseudomonas aeruginosa isolates, recovered from inpatients at Hospital de Clínicas in Buenos Aires. Both, phenotypic and genotypic methods detected the presence of carbapenemases in 10 (11%) isolates, corresponding to VIM-11 in 7/10 and VIM-2 in the others. Codifying genes were all included in class 1 integrons, upstream genes coding for aminoglycoside modifying enzymes. One hundred percent sensitivity and specificity was achieved by the metallo-beta-lactamases phenotypic screening method using EDTA (1 micromol) disks in the Pseudomonas aeruginosa isolates included in this study. Sensitivity to aztreonam in carbapenem resistant isolates was suspicious of the presence of these enzymes.

Argentina↗
PubMed2006

[Origin, evolution, and migration of drug resistance genes].

Current views on the mechanisms responsible for the emergence of multiple drug resistance in clinical bacterial isolates are considered. Hypotheses on the origin of resistance genes derived from determinants of actinomycetes, antibiotic producers, and chromosomal genes of bacteria involved in cellular metabolism are reviewed. The mechanisms underlying the diffusion of resistance determinants by means of bacterial mobile elements (plasmids, transposons, and integrons) are discussed. Examples of the horizontal transfer of resistance determinants between Gram-positive and Gram-negative bacteria are presented.

Amino Acid Sequence↗
PubMed1995

[Antibiotic resistance--an ambivalence of attitudes. As of now, the bacteria are in advantage].

The value of the precious medical asset that antibiotics constitute is contimualby being eroded by the spread of resistance. For some time that bacterial world has been adapting itself to contend with the toxic assault of man-made poisons, antibiotics, by developing resistance in a very rapid process of evolutionary changes occurring before our very eyes. This evolutionary adaptation is an example of natural genetic engineering entailing an interchange between bacteria of genes conferring antibiotic resistance. Trimethoprim resistance is an example where numerous genes of unknown origin (some closely interrelated), expressing drug-resistant dihydrofolate reductases, move among human commensals and pathogens. They have been shown to move as gene cassettes in and out of the recently characterised integron structure occurring in many pathogens. They are also carried by various transposons such as Tn7, or Tn5393 originally observed in a plant pathogen, Erwinia amylovora. Betalactam resistance is another example of natural genetic engineering, where new betalactamases are continually emerging, and individual enzyme substrate specificity is modified by point mutation. At present, betalactamase mutants resistant to all commercially available betalactams, including clavulanic acid used in combination with betalactam antibiotics, are to be found in clinical isolates. Thus, currently bacteria seem to be triumphing in the running battle between the pharmaceutical industry and the bacterial world, the former introducing one new antibiotic variant after another, to which bacteria promptly develop resistance by manipulating their own genomes.

Animals↗
PubMed1993

[Cloning and nucleotide sequence determination of the aadB gene from a Salmonella oranienburg strain].

Cloning and nucleotide sequence determination of the aadB gene and boundary DNA fragments from a high molecular weight plasmid of Salmonella oranienburg were performed. The data on the restriction mapping showed that the aadB gene was located within the integrone. Analysis of the nucleotide sequence of the cloned fragment revealed a high level conservative nature of the aadB gene and boundary DNA areas.

Base Sequence↗
PubMed1993

[Characterization of trimethoprim resistance in Shigella].

Ninety-seven Shigella strains from 1982 to 1987 were isolated. When these isolates were tested with minimal inhibitory concentrations of trimethoprim, twenty-two were found to be resistant. Among these, 10 were found to be S. flexneri, and 12 to be S. sonnei. In addition, all of these 22 isolates were found to have multiple drug resistance. In order to determine the type of dihydrofolate reductase (DHFR) genes in these 22 trimethoprim-resistant isolates, colony hybridization with probes representing types I, II, III and V DHFR, were used. The results revealed the presence of type I DHFR gene in all of these isolates. Further southern hybridization indicated that the type I DHFR gene was located on plasmids. In order to determine whether a trimethoprim resistant gene existed as a functional transposable element in these isolates, we used a specific probe to detect the prevalence of Tn7. However, no positive hybridization was found. The relationship between the trimethoprim resistant gene and integron is characterized by the fact that the integrase gene, in our study, was frequently found in all of the 22 resistant isolates. These results indicate that trimethoprim resistant genes might transfer among bacteria via site-specific integration.

Serotyping↗
PubMed1997

[Biochemical and genetic mechanisms for bacteria to acquire aminoglycoside antibiotic resistance].

Aminoglycoside (AG)-modifying enzymes are the major biochemical basis for the AG resistance of clinically-occurring bacteria. Recent AG resistance profiles can be characterized by the involvement of AAC(6') in combination with other modifying enzymes in Gram negative bacteria. AAC(6')/APH(2") in Staphylococcus aureus is also remarkable. Genetic basis for the emergence or alteration of AG resistance profiles includes point mutations in the regulatory region or specific sites of the coding region of AG-modifying enzyme genes, and rearrangement of the genes caused by transposon and/or integron. In addition, semisynthetic AG antibiotics such as amikacin, arbekacin (ABK) and isepamicin were also reviewed for their stability to AG-modifying enzymes. ABK that has been widely used as an anti-MRSA drug in Japan is distinct from the other AGs because its monoacetylated derivatives (3"-N-acetylABK and 2'-N-acetylABK) by AG acetyltransferases, AAC(3) and AAC(2'), respectively, retain clear antibiotic activities. Based on this novel aspect and the lack of modification sites for APH(3') and ANT(4'), ABK should be regarded as the most refractory AG for bacteria to acquire resistance.

Acetyltransferases↗
PubMed2005

A variant type of Vibrio cholerae SXT element in a multidrug-resistant strain of Vibrio fluvialis.

Vibrio fluvialis strain H-08942 was isolated from an infant aged 6 months who was suffering from cholera-like diarrhea in India. This strain showed the typical multidrug-resistance phenotype of an SXT element. It was resistant to sulfamethoxazole (Su), trimethoprim (Tm), chloramphenicol (Cm) and streptomycin (Sm), in addition to other antibiotics such as ampicillin (Am), furazolidone (Fz), nalidixic acid (Na), and gentamicin (Gm). The SXT element is a Vibrio cholerae-derived integrative and conjugative element (ICE) that has also been referred to as a conjugative transposon. Our goal was to find a relationship between these resistant phenotypes and the presence of the SXT element in this unique strain. By using PCR, we detected the antibiotic resistance genes, the integrase gene and the attP attachment site of SXT element. Cloning and DNA sequencing results showed that both the SXT integrase gene and its attP site of V. fluvialis were similar but not identical to those of V. cholerae. The SXT integrase gene of V. fluvialis has a 99% identity to that of V. cholerae, and the attP site of SXT of V. fluvialis is variant and shorter (641 bp) than that of V. cholerae (785 bp). It was possible for the SXT of V. fluvialis to be transferred by conjugation to a laboratory strain of Escherichia coli. Here, we report the detection of a variant SXT element in species other than V. cholerae, with molecular characterization and analysis of its integrase gene and its attP site.

Conjugation, Genetic↗
PubMed2005

Acquired sulphonamide resistance genes in faecal Escherichia coli from healthy children in Bolivia and Peru.

Antimicrobial resistance and sulphonamide resistance determinants were studied in 20 co-trimoxazole resistant Escherichia coli in faecal samples from healthy children in Bolivia and Peru. Methods used were disc diffusion susceptibility tests, PCR, sequence analysis and plasmid conjugation assays. All isolates but one were resistant to at least two different classes of antimicrobials; 19 isolates also carried at least one sul-gene. The most frequent gene was sul2 followed by sul1 and sul3, which was detected in one isolate. This is the first observation of sul3 on the American continent. In conclusion, the high prevalence of sul-genes in this material of faecal commensal E. coli isolates points to a potential role of the faecal flora in the emergence and spread of antimicrobial resistance.

Anti-Infective Agents↗
PubMed2005

Bacterial resistance to silver in wound care.

Ionic silver exhibits antimicrobial activity against a broad range of micro-organisms. As a consequence, silver is included in many commercially available healthcare products. The use of silver is increasing rapidly in the field of wound care, and a wide variety of silver-containing dressings are now commonplace (e.g. Hydrofiber dressing, polyurethane foams and gauzes). However, concerns associated with the overuse of silver and the consequent emergence of bacterial resistance are being raised. The current understanding of the biochemical and molecular basis behind silver resistance has been documented since 1998. Despite the sporadic evidence of bacterial resistance to silver, there have been very few studies undertaken and documented to ascertain its prevalence. The risks of antibacterial resistance developing from the use of biocides may well have been overstated. It is proposed that hygiene should be emphasized and targeted towards those applications that have demonstrable benefits in wound care. It is the purpose of this review to assess the likelihood of widespread resistance to silver and the potential for silver to induce cross-resistance to antibiotics, in light of its increasing usage within the healthcare setting.

Anti-Infective Agents, Local↗
PubMed2005

Retron reverse transcriptase (rrtT) can be lost in multidrug resistant Salmonella enterica serovar Typhimurium DT 104 strains and influences virulence for mice.

In Salmonella enterica serovar Typhimurium, retron reverse transcriptase (rrtT), which is part of St 85 retron, is quite ubiquitous and is located in the thdF -yidY intergenic region. In this study, we showed that rrtT is relatively unstable in multidrug resistant, Salmonella genomic island 1 (SGI 1) positive strains. Out of 365 field strains, 55 were free of retron. In 54 of the rrtT negative strains, the excision must have occurred by the same mechanism in which the rrtT together with five other genes was excised. Altogether 8164 bp was missing in the chromosome of the rrtT negative strains. Since the deletion happened exactly between the right inverted repeat of IS 6100 and inside the yieE gene, we propose that intramolecular transposition of IS 6100 followed by homologous recombination was responsible for the excision. Excision of retron together with the right end of SGI 1 may also result in its stabilisation in the Salmonella typhimurium genome. Experimental deletion of rrtT resulted in an accelerated course of infection in orally infected mice. Since the retron excision occurred exclusively in multidrug resistant S. typhimurium, it cannot be excluded that such strains may increase their virulence in the future.

Animals↗
PubMed2006

Environment arrays: a possible approach for predicting changes in waterborne bacterial disease potential.

Current molecular techniques for identifying bacteria in water have proven useful, but they are not reliably predictive of impending disease outbreaks. Genomics-based approaches will help to detect the presence of pathogens quickly and well before they grow into a population that poses a risk to public health. We suggest that genomics is only one component of the toolbox that will be needed to identify emerging waterborne threats. We propose a methodology beyond genomics, based on activity in the mobile genome. This approach makes use of a new device called an environment array. The array will depend upon the same research necessary for genomics-based detection, but will not require an a priori knowledge of virulence genes. Environment arrays are assembled from molecular profiles of the infectious elements that transfer between bacteria. The advantage of the array is that it monitors the activity of the mobile genome, rather than the presence of particular DNA sequences. Environmental arrays should thus be many times more sensitive than traditional hybridization or PCR-based techniques that target already-known DNA sequences. Mobile elements are known to respond to new environmental conditions that may correlate with a chemical contamination or the bloom of bacterial pathogens, potentially allowing for a much broader application in detecting unknown or unanticipated biological and chemical contaminants.

Bacteria↗
PubMed2006

Genetic linkage and horizontal gene transfer, the roots of the antibiotic multi-resistance problem.

Bacteria carrying resistance genes for many antibiotics are moving beyond the clinic into the community, infecting otherwise healthy people with untreatable and frequently fatal infections. This state of affairs makes it increasingly important that we understand the sources of this problem in terms of bacterial biology and ecology and also that we find some new targets for drugs that will help control this growing epidemic. This brief and eclectic review takes the perspective that we have too long thought about the problem in terms of treatment with or resistance to a single antibiotic at a time, assuming that dissemination of the resistance gene was affected by simple vertical inheritance. In reality antibiotic resistance genes are readily transferred horizontally, even to and from distantly related bacteria. The common agents of bacterial gene transfer are described and also one of the processes whereby nonantibiotic chemicals, specifically toxic metals, in the environment can select for and enrich bacteria with antibiotic multiresistance. Lastly, some speculation is offered on broadening our perspective on this problem to include drugs directed at compromising the ability of the mobile elements themselves to replicate, transfer, and recombine, that is, the three "infrastructure" processes central to the movement of genes among bacteria.

Animal Husbandry↗
PubMed2005

Genetic basis of antimicrobial drug resistance in clinical isolates of Salmonella enterica serotype Hadar from a Spanish region.

The genetic bases of antimicrobial drug resistance (R) of 79 Salmonella enterica serotype Hadar clinical isolates (recovered during 1995-2001 in a Spanish region) was investigated. The isolates showed a limited genomic variation, as demonstrated by PFGE analysis using XbaI (three profiles, S>or=0.77) and BlnI (seven profiles, S>or=0.49; with 95% of the isolates falling into two clusters, S>or=0.75). Thirteen R-profiles, ranging from susceptible to multidrug resistant, were recognized. All susceptible isolates (14%) were recovered before or during 1998, when multidrug resistance (MDR) was still uncommon (20% from 1995-1998). In later years, the percentage of MDR increased considerably (92% in 2001). Resistance to nalidixic acid, tetracycline, streptomycin and ampicillin-cefalotin, encoded by gyrA-Asp87/Asn, tet(A), strA/B, and bla (TEM) genes, respectively, were the most common, appearing together in 38% of the isolates. In all tetracycline- and streptomycin-resistant isolates, strA/B and tet(A) were chromosomally located, whereas bla (TEM) was plasmid-born. Five different bla (TEM) plasmids (pUO-ShR1 to pUO-ShR5, of about 9.4, 23, 30, 45, and 95 kb, respectively) were identified. pUO-ShR3 and pUO-ShR5 harbored additional R-genes: [dfrA1] and [acc(3)IV-strA/B], respectively. pUO-Sh2, pUO-Sh3, pUO-ShR4, and pUO-Sh5 were self-transferable, and the latter could also mobilize pUOShR1. The reported data constitute a useful background for further epidemiological studies of MDR in S. Hadar.

Drug Resistance, Multiple, Bacterial↗
PubMed2006

The HicAB cassette, a putative novel, RNA-targeting toxin-antitoxin system in archaea and bacteria.

Toxin-antitoxin systems (TAS) are abundant, diverse, horizontally mobile gene modules that encode powerful resistance mechanisms in prokaryotes. We use the comparative-genomic approach to predict a new TAS that consists of a two-gene cassette encoding uncharacterized HicA and HicB proteins. Numerous bacterial and archaeal genomes encode from one to eight HicAB modules which appear to be highly prone to horizontal gene transfer. The HicB protein (COG1598/COG4226) has a partially degraded RNAse H fold, whereas HicA (COG1724) contains a double-stranded RNA-binding domain. The stable combination of these two domains suggests a link to RNA metabolism, possibly, via an RNA interference-type mechanism. In most HicB proteins, the RNAse H-like domain is fused to a DNA-binding domain, either of the ribbon-helix-helix or of the helix-turn-helix class; in other TAS, proteins containing these DNA-binding domains function as antitoxins. Thus, the HicAB module is predicted to be a novel TAS whose mechanism involves RNA-binding and, possibly, cleavage.

Antitoxins↗
PubMed2003

Monitoring and identifying antibiotic resistance mechanisms in bacteria.

Sub-therapeutic administration of antibiotics to animals is under intense scrutiny because they contribute to the dissemination of antibiotic-resistant bacteria into the food chain. Studies suggest that there is a link between the agricultural use of antibiotics and antibiotic-resistant human infections. Antibiotic-resistant organisms from animal and human wastes reenter the human and animal populations through a number of pathways including natural waters, irrigation water, drinking water, and vegetables and foods. Antibiotic usage in the United States for animal production (disease prevention and growth promotion) is estimated to be 18 million pounds annually. As much as 25 to 75% of the antibiotics administered to feedlot animals are excreted unaltered in feces. Because about 180 million dry tons of livestock and poultry waste is generated annually in the United States, it is not surprising that animal-derived antibiotic-resistant organisms are found contaminating groundwater, surface water, and food crops. It is extremely important to clearly understand the molecular mechanisms that could potentially cause lateral or horizontal gene transfer of antibiotic resistance genes among bacteria. Once the mechanisms and magnitude of resistance gene transfer are clearly understood and quantified, strategies can be instituted to reduce the potential for dissemination of these genes.

Animal Husbandry↗