Novel Ambler class A beta-lactamase LAP-1 and its association with the plasmid-mediated quinolone resistance determinant QnrS1

Comprehensive Analysis of Virulence Determinants and Genomic Islands of blaNDM-1-Producing Enterobacter hormaechei Clinical Isolates from Greece

Nosocomial outbreaks of multidrug-resistant (MDR) Enterobacter cloacae complex (ECC) are often reported worldwide, mostly associated with a small number of multilocus-sequence types of E. hormaechei and E. cloacae strains. In Europe, the largest clonal outbreak of blaNDM-1-producing ECC has been recently reported, involving an ST182 E. hormaechei strain in a Greek teaching hospital. In the current study, we aimed to further investigate the genetic make-up of two representative outbreak isolates. Comparative genomics of whole genome sequences (WGS) was performed, including whole genome-based taxonomic analysis and in silico prediction of virulence determinants of the bacterial cell surface, plasmids, antibiotic resistance genes and virulence factors present on genomic islands. The enterobacterial common antigen and the colanic antigen of the cell surface were identified in both isolates, being similar to the gene clusters of the E. hormaechei ATCC 49162 and E. cloacae ATCC 13047 type strains, whereas the two strains possessed different gene clusters encoding lipopolysaccharide O-antigens. Other virulence factors of the bacterial cell surface, such as flagella, fimbriae and pili, were also predicted to be encoded by gene clusters similar to those found in Enterobacter spp. and other Enterobacterales. Secretion systems and toxin-antitoxin systems, which also contribute to pathogenicity, were identified. Both isolates harboured resistance genes to multiple antimicrobial classes, including β-lactams, aminoglycosides, quinolones, chloramphenicol, trimethoprim, sulfonamides and fosfomycin; they carried blaTEM-1, blaOXA-1, blaNDM-1, and one of them also carried blaCTXM-14, blaCTXM-15 and blaLAP-2 plasmidic alleles. Our comprehensive analysis of the WGS assemblies revealed that blaNDM-1-producing outbreak isolates possess components of the bacterial cell surface as well as genomic islands, harbouring resistance genes to several antimicrobial classes and various virulence factors. Differences in the plasmids carrying β-lactamase genes between the two strains have also shown diverse modes of acquisition and an ongoing evolution of these mobile elements.

Identification and Genetic Characterization of Conjugative Plasmids Encoding Coresistance to Ciprofloxacin and Cephalosporin in Foodborne Vibrio spp

Plasmid-mediated quinolone resistance (PMQR) determinants, such as qnrVC genes, have been widely reported in Vibrio spp. while other types of PMQR genes were rarely reported in these bacteria. This study characterized the phenotypic and genotypic features of foodborne Vibrio spp. carrying qnrS, a key PMQR gene in Enterobacteriaceae. Among a total of 1,811 foodborne Vibrio isolates tested, 34 (1.88%) were found to harbor the qnrS gene. The allele qnrS2 was the most prevalent, but coexistence with other qnr alleles was common. Missense mutations in the quinolone resistance-determining region (QRDR) of the gyrA and parC genes were only found in 11 of the 34 qnrS-bearing isolates. Antimicrobial susceptibility tests showed that all 34 qnrS-bearing isolates were resistant to ampicillin and that a high percentage also exhibited resistance to cefotaxime, ceftriaxone, and trimethoprim-sulfamethoxazole. Genetic analysis showed that these phenotypes were attributed to a diverse range of resistance elements that the qnrS-bearing isolates harbored. The qnrS2 gene could be found in both the chromosome and plasmids; the plasmid-borne qnrS2 genes could be found on both conjugative and nonconjugative plasmids. pAQU-type qnrS2-bearing conjugative plasmids were able to mediate expression of phenotypic resistance to both ciprofloxacin and cephalosporins. Transmission of this plasmid among Vibrio spp. would speed up the emergence of multidrug-resistant (MDR) pathogens that are resistant to the most important antibiotics used in treatment of Vibrio infections, suggesting that close monitoring of emergence and dissemination of MDR Vibrio spp. in both food samples and clinical settings is necessary. IMPORTANCE Vibrio spp. used to be very susceptible to antibiotics. However, resistance to clinically important antibiotics, such as cephalosporins and fluoroquinolones, among clinically isolated Vibrio strains is increasingly common. In this study, we found that plasmid-mediated quinolone resistance (PMQR) genes, such as qnrS, that have not been previously reported in Vibrio spp. can now be detected in food isolates. The qnrS2 gene alone could mediate expression of ciprofloxacin resistance in Vibrio spp.; importantly, this gene could be found in both the chromosome and plasmids. The plasmids that harbor the qnrS2 gene could be both conjugative and nonconjugative, among which the pAQU-type qnrS2-bearing conjugative plasmids were able to mediate expression of resistance to both ciprofloxacin and cephalosporins. Transmission of this plasmid among Vibrio spp. would accelerate the emergence of multidrug-resistant pathogens.

Molecular mechanisms associated with quinolone resistance in Enterobacteriaceae: review and update

BACKGROUND

Quinolones are broad-spectrum antibiotics, which are used for the treatment of different infectious diseases associated with Enterobacteriaceae. During recent decades, the wide use as well as overuse of quinolones against diverse infections has led to the emergence of quinolone-resistant bacterial strains. Herein, we present the development of quinolone antibiotics, their function and also the different quinolone resistance mechanisms in Enterobacteriaceae by reviewing recent literature.

METHODS

All data were extracted from Google Scholar search engine and PubMed site, using keywords; quinolone resistance, Enterobacteriaceae, plasmid-mediated quinolone resistance, etc.

RESULTS AND CONCLUSION

The acquisition of resistance to quinolones is a complex and multifactorial process. The main resistance mechanisms consist of one or a combination of target-site gene mutations altering the drug-binding affinity of target enzymes. Other mechanisms of quinolone resistance are overexpression of AcrAB-tolC multidrug-resistant efflux pumps and downexpression of porins as well as plasmid-encoded resistance proteins including Qnr protection proteins, aminoglycoside acetyltransferase (AAC(6')-Ib-cr) and plasmid-encoded active efflux pumps such as OqxAB and QepA. The elucidation of resistance mechanisms will help researchers to explore new drugs against the resistant strains.

Whole-Genome Sequence Analysis of an Extensively Drug-Resistant Salmonella enterica Serovar Agona Isolate from an Australian Silver Gull (Chroicocephalus novaehollandiae) Reveals the Acquisition of Multidrug Resistance Plasmids

Although most of the approximately 94 million annual human cases of gastroenteritis due to Salmonella enterica resolve without medical intervention, antimicrobial therapy is recommended for patients with severe disease. Wild birds can be natural hosts of Salmonella that pose a threat to human health; however, multiple-drug-resistant serovars of S. enterica have rarely been described. In 2012, silver gull (Chroicocephalus novaehollandiae) chicks at a major breeding colony were shown to host Salmonella, most isolates of which were susceptible to antibiotics. However, multiple-drug-resistant (MDR) Escherichia coli with resistance to carbapenems, ceftazidime, and fluoroquinolones was reported from this breeding colony. In this paper, we describe a novel MDR Salmonella strain subsequently isolated from the same breeding colony. SG17-135, an isolate of S. enterica with phenotypic resistance to 12 individual antibiotics but only nine antibiotic classes including penicillins, cephalosporins, monobactams, macrolides, fluoroquinolones, aminoglycosides, dihydrofolate reductase inhibitors (trimethoprim), sulfonamides, and glycylcyclines was recovered from a gull chick in 2017. Whole-genome sequence (WGS) analysis of SG17-135 identified it as Salmonella enterica serovar Agona (S Agona) with a chromosome comprising 4,813,284 bp, an IncHI2 ST2 plasmid (pSG17-135-HI2) of 311,615 bp, and an IncX1 plasmid (pSG17-135-X) of 27,511 bp. pSG17-135-HI2 housed a complex resistance region comprising 16 antimicrobial resistance genes including bla _CTX-M-55 The acquisition of MDR plasmids by S. enterica described here poses a serious threat to human health. Our study highlights the importance of taking a One Health approach to identify environmental reservoirs of drug-resistant pathogens and MDR plasmids.IMPORTANCE Defining environmental reservoirs hosting mobile genetic elements that shuttle critically important antibiotic resistance genes is key to understanding antimicrobial resistance (AMR) from a One Health perspective. Gulls frequent public amenities, parklands, and sewage and other waste disposal sites and carry drug-resistant Escherichia coli Here, we report on SG17-135, a strain of Salmonella enterica serovar Agona isolated from the cloaca of a silver gull chick nesting on an island in geographic proximity to the greater metropolitan area of Sydney, Australia. SG17-135 is closely related to pathogenic strains of S Agona, displays resistance to nine antimicrobial classes, and carries important virulence gene cargo. Most of the antibiotic resistance genes hosted by SG17-135 are clustered on a large IncHI2 plasmid and are flanked by copies of IS26 Wild birds represent an important link in the evolution and transmission of resistance plasmids, and an understanding of their behavior is needed to expose the interplay between clinical and environmental microbial communities.

High genetic diversity of Vibrio parahaemolyticus isolated from tidal water and mud of southern coast of South Korea

A horizontal, fluorophore-enhanced, repetitive extragenic palindromic-polymerase chain reaction (rep-PCR) DNA fingerprinting technique was adapted to examine the genotypic richness and source differentiation of Vibrio parahaemolyticus (n = 1749) isolated from tidal water and mud of southern coast of South Korea. The number of unique genotypes observed from June (163, 51.9%), September (307, 63.9%), December (205, 73.8%) and February (136, 74.7%), indicating a high degree of genetic diversity. Contrary, lower genetic diversity was detected in April (99, 46.8%), including predominant genotypes comprised >30 V. parahaemolyticus isolates. Jackknife analysis indicated that 65.1% tidal water isolates and 87.1% mud isolates were correctly assigned to their source groups. Sixty-nine isolates of pathogenic V. parahaemolyticus were clustered into two groups, separated by sampling month, source of isolation and serogroups. Serotypes O1, O4, O5, O10/O12 and O11 were the dominant serovariants, while serotypes O3/O13 were highly detected in April where there were no pathogenic V. parahaemolyticus isolates. Most of the V. parahaemolyticus isolates were resistant to ampicillin, ceftazidime and sulfamethoxazole. Interestingly, four V. parahaemolyticus isolates resistant to carbepenem did not contain the known carbapenemase-encoding gene, but possess an extended-spectrum β-lactamase blaTEM.

Transferable Mechanisms of Quinolone Resistance from 1998 Onward

While the description of resistance to quinolones is almost as old as these antimicrobial agents themselves, transferable mechanisms of quinolone resistance (TMQR) remained absent from the scenario for more than 36 years, appearing first as sporadic events and afterward as epidemics. In 1998, the first TMQR was soundly described, that is, QnrA. The presence of QnrA was almost anecdotal for years, but in the middle of the first decade of the 21st century, there was an explosion of TMQR descriptions, which definitively changed the epidemiology of quinolone resistance. Currently, 3 different clinically relevant mechanisms of quinolone resistance are encoded within mobile elements: (i) target protection, which is mediated by 7 different families of Qnr (QnrA, QnrB, QnrC, QnrD, QnrE, QnrS, and QnrVC), which overall account for more than 100 recognized alleles; (ii) antibiotic efflux, which is mediated by 2 main transferable efflux pumps (QepA and OqxAB), which together account for more than 30 alleles, and a series of other efflux pumps (e.g., QacBIII), which at present have been sporadically described; and (iii) antibiotic modification, which is mediated by the enzymes AAC(6')Ib-cr, from which different alleles have been claimed, as well as CrpP, a newly described phosphorylase.

Plasmid-mediated quinolone resistance: Two decades on

After two decades of the discovery of plasmid-mediated quinolone resistance (PMQR), three different mechanisms have been associated to this phenomenon: target protection (Qnr proteins, including several families with multiple alleles), active efflux pumps (mainly QepA and OqxAB pumps) and drug modification [AAC(6')-Ib-cr acetyltransferase]. PMQR genes are usually associated with mobile or transposable elements on plasmids, and, in the case of qnr genes, are often incorporated into sul1-type integrons. PMQR has been found in clinical and environmental isolates around the world and appears to be spreading. Although the three PMQR mechanisms alone cause only low-level resistance to quinolones, they can complement other mechanisms of chromosomal resistance to reach clinical resistance level and facilitate the selection of higher-level resistance, raising a threat to the treatment of infections by microorganisms that host these mechanisms.

A Structure-Based Classification of Class A β-Lactamases, a Broadly Diverse Family of Enzymes

For medical biologists, sequencing has become a commonplace technique to support diagnosis. Rapid changes in this field have led to the generation of large amounts of data, which are not always correctly listed in databases. This is particularly true for data concerning class A β-lactamases, a group of key antibiotic resistance enzymes produced by bacteria. Many genomes have been reported to contain putative β-lactamase genes, which can be compared with representative types. We analyzed several hundred amino acid sequences of class A β-lactamase enzymes for phylogenic relationships, the presence of specific residues, and cluster patterns. A clear distinction was first made between dd-peptidases and class A enzymes based on a small number of residues (S70, K73, P107, 130SDN132, G144, E166, 234K/R, 235T/S, and 236G [Ambler numbering]). Other residues clearly separated two main branches, which we named subclasses A1 and A2. Various clusters were identified on the major branch (subclass A1) on the basis of signature residues associated with catalytic properties (e.g., limited-spectrum β-lactamases, extended-spectrum β-lactamases, and carbapenemases). For subclass A2 enzymes (e.g., CfxA, CIA-1, CME-1, PER-1, and VEB-1), 43 conserved residues were characterized, and several significant insertions were detected. This diversity in the amino acid sequences of β-lactamases must be taken into account to ensure that new enzymes are accurately identified. However, with the exception of PER types, this diversity is poorly represented in existing X-ray crystallographic data.

Plasmid-mediated quinolone resistance

Three mechanisms for plasmid-mediated quinolone resistance (PMQR) have been discovered since 1998. Plasmid genes qnrA, qnrB, qnrC, qnrD, qnrS, and qnrVC code for proteins of the pentapeptide repeat family that protects DNA gyrase and topoisomerase IV from quinolone inhibition. The qnr genes appear to have been acquired from chromosomal genes in aquatic bacteria, are usually associated with mobilizing or transposable elements on plasmids, and are often incorporated into sul1-type integrons. The second plasmid-mediated mechanism involves acetylation of quinolones with an appropriate amino nitrogen target by a variant of the common aminoglycoside acetyltransferase AAC(6')-Ib. The third mechanism is enhanced efflux produced by plasmid genes for pumps QepAB and OqxAB. PMQR has been found in clinical and environmental isolates around the world and appears to be spreading. The plasmid-mediated mechanisms provide only low-level resistance that by itself does not exceed the clinical breakpoint for susceptibility but nonetheless facilitates selection of higher-level resistance and makes infection by pathogens containing PMQR harder to treat.

Prevalence of Quinolone Resistance Genes Among Extended-Spectrum B-Lactamase-Producing Escherichia coli in Mashhad, Iran

Background:

Escherichia coli is an important bacterial species based on incidence and associated infection severity. Some E. coli strains produce extended-spectrum beta lactamase (ESBL) and are called ESBL-producing E. coli. These strains are resistant to most classes of cephalosporin and a number of other classes of antibiotics. Plasmids carrying qnr genes have been found to transmit quinolone resistance.

Objectives:

The aim of this study was to determine the frequency of qnr genes in ESBL-producing and non-ESBL-producing E. coli isolated from outpatient and hospitalized patient clinical specimens from Imam Reza hospital in Mashhad, Iran.

Materials and Methods:

Two hundred E. coli strains, isolated from different clinical specimens were used. ESBL-producing E. coli were detected by determining susceptibility to ceftazidime, cefotaxime, and cefpodoxime with the phenotypic confirmatory test (PCT). PCR analysis was employed to detect the qnrA, qnrB, qnrS, bla_TEM, and bla_SHV genes.

Results:

Eighty-six (43%) isolates were ciprofloxacin-resistant. The PCT identified 85 (42.5%) of 200 E. coli isolates as ESBL-producing. The bla_TEM, bla_SHV, qnrA, qnrB, and qnrS gene were found in 65 (76.47%), 23 (27%), 63 (31%), 34 (17%), and 14 (7%) isolates, respectively.

Conclusions:

The high prevalence of quinolone resistance genes, which indicates antibiotic resistance, in the Imam Reza Hospital of Mashhad is a major concern. Hence, the antibiotics prescription policy should be revised, and infection control measures should be improved.

Genetic characterization of three qnrS1-harbouring multidrug-resistance plasmids and qnrS1-containing transposons circulating in Ho Chi Minh City, Vietnam

Plasmid-mediated quinolone resistance (PMQR) refers to a family of closely related genes that confer decreased susceptibility to fluoroquinolones. PMQR genes are generally associated with integrons and/or plasmids that carry additional antimicrobial resistance genes active against a range of antimicrobials. In Ho Chi Minh City (HCMC), Vietnam, we have previously shown a high frequency of PMQR genes within commensal Enterobacteriaceae. However, there are limited available sequence data detailing the genetic context in which the PMQR genes reside, and a lack of understanding of how these genes spread across the Enterobacteriaceae. Here, we aimed to determine the genetic background facilitating the spread and maintenance of qnrS1, the dominant PMQR gene circulating in HCMC. We sequenced three qnrS1-carrying plasmids in their entirety to understand the genetic context of these qnrS1-embedded plasmids and also the association of qnrS1-mediated quinolone resistance with other antimicrobial resistance phenotypes. Annotation of the three qnrS1-containing plasmids revealed a qnrS1-containing transposon with a closely related structure. We screened 112 qnrS1-positive commensal Enterobacteriaceae isolated in the community and in a hospital in HCMC to detect the common transposon structure. We found the same transposon structure to be present in 71.4 % (45/63) of qnrS1-positive hospital isolates and in 36.7 % (18/49) of qnrS1-positive isolates from the community. The resulting sequence analysis of the qnrS1 environment suggested that qnrS1 genes are widely distributed and are mobilized on elements with a common genetic background. Our data add additional insight into mechanisms that facilitate resistance to multiple antimicrobials in Gram-negative bacteria in Vietnam.

Mobile insertion cassette elements found in small non-transmissible plasmids in Proteeae may explain qnrD mobilization

qnrD is a plasmid mediated quinolone resistance gene from unknown origin, recently described in Enterobacteriaceae. It encodes a pentapeptide repeat protein 36-60% different from the other Qnr (A, B, C, S and VC). Since most qnrD-positive strains were described as strains belonging to Proteus or Providencia genera, we hypothesized that qnrD originated in Proteeae before disseminating to other enterobacterial species. We screened 317 strains of Proteeae for qnrD and its genetic support by PCR. For all the seven qnrD-positive strains (4 Proteus mirabilis, 1 Proteus vulgaris and 2 Providencia rettgeri) the gene was carried onto a small non-transmissible plasmid, contrarily to other qnr genes that are usually carried onto large multi-resistant plasmids. Nucleotide sequences of the qnrD-bearing plasmids were 96% identical. Plasmids contained 3 ORFs apart from qnrD and belonged to an undescribed incompatibility group. Only one plasmid, in P. vulgaris, was slightly different with a 1,568-bp insertion between qnrD and its promoter, leading to absence of quinolone resistance. We sought for similar plasmids in 15 reference strains of Proteeae, but which were tested negative for qnrD, and found a 48% identical plasmid (pVERM) in Providencia vermicola. In order to explain how qnrD could have been inserted into such native plasmid, we sought for gene mobilization structures. qnrD was found to be located within a mobile insertion cassette (mic) element which sequences are similar to one mic also found in pVERM. Our conclusions are that (i) the small non-transmissible qnrD-plasmids described here may result from the recombination between an as-yet-unknown progenitor of qnrD and pVERM, (ii) these plasmids are maintained in Proteeae being a qnrD reservoir (iii) the mic element may explain qnrD mobilization from non-transmissible plasmids to mobilizable or conjugative plasmids from other Enterobacteriaceae, (iv) they can recombined with larger multiresistant plasmids conjugated in Proteeae.

Plasmid-mediated quinolone resistance--current knowledge and future perspectives

Quinolones are a group of antimicrobial agents that were serendipitously discovered as byproducts of the synthesis of chloroquine. Chemical modifications, such as the addition of fluorine or piperazine, resulted in the synthesis of third- and fourth-generation fluoroquinolones, with broad-spectrum antimicrobial actions against aerobic or anaerobic, Gram-positive or Gram-negative bacteria. The efficacy and consequent widespread use of quinolones and fluoroquinolones has led to a steady global increase in resistance, mediated via gene mutations, alterations in efflux or cell membranes and plasmid-conferred resistance. The first plasmid-mediated quinolone resistance gene, qnrA1, was detected in 1998. Since then, many other genes have been identified and the underlying mechanisms of resistance have been elucidated. This review provides an overview of quinolone resistance, with particular emphasis on plasmid-mediated resistance.

The co-selection of fluoroquinolone resistance genes in the gut flora of Vietnamese children

Antimicrobial consumption is one of the major contributing factors facilitating the development and maintenance of bacteria exhibiting antimicrobial resistance. Plasmid-mediated quinolone resistance (PMQR) genes, such as the qnr family, can be horizontally transferred and contribute to reduced susceptibility to fluoroquinolones. We performed an observational study, investigating the copy number of PMQR after antimicrobial therapy. We enrolled 300 children resident in Ho Chi Minh City receiving antimicrobial therapy for acute respiratory tract infections (ARIs). Rectal swabs were taken on enrollment and seven days subsequently, counts for Enterobacteriaceae were performed and qnrA, qnrB and qnrS were quantified by using real-time PCR on metagenomic stool DNA. On enrollment, we found no association between age, gender or location of the participants and the prevalence of qnrA, qnrB or qnrS. Yet, all three loci demonstrated a proportional increase in the number of samples testing positive between day 0 and day 7. Furthermore, qnrB demonstrated a significant increase in copy number between paired samples (p<0.001; Wilcoxon rank-sum), associated with non-fluoroquinolone combination antimicrobial therapy. To our knowledge, this is the first study describing an association between the use of non-fluoroquinolone antimicrobials and the increasing relative prevalence and quantity of qnr genes. Our work outlines a potential mechanism for the selection and maintenance of PMQR genes and predicts a strong effect of co-selection of these resistance determinants through the use of unrelated and potentially unnecessary antimicrobial regimes.

Plasmid-Mediated Quinolone Resistance; Interactions between Human, Animal, and Environmental Ecologies

Resistance to quinolones and fluoroquinolones is being increasingly reported among human but also veterinary isolates during the last two to three decades, very likely as a consequence of the large clinical usage of those antibiotics. Even if the principle mechanisms of resistance to quinolones are chromosome-encoded, due to modifications of molecular targets (DNA gyrase and topoisomerase IV), decreased outer-membrane permeability (porin defect), and overexpression of naturally occurring efflux, the emergence of plasmid-mediated quinolone resistance (PMQR) has been reported since 1998. Although these PMQR determinants confer low-level resistance to quinolones and/or fluoroquinolones, they are a favorable background for selection of additional chromosome-encoded quinolone resistance mechanisms. Different transferable mechanisms have been identified, corresponding to the production of Qnr proteins, of the aminoglycoside acetyltransferase AAC(6′)-Ib-cr, or of the QepA-type or OqxAB-type efflux pumps. Qnr proteins protect target enzymes (DNA gyrase and type IV topoisomerase) from quinolone inhibition. The AAC(6′)-Ib-cr determinant acetylates several fluoroquinolones, such as norfloxacin and ciprofloxacin. Finally, the QepA and OqxAB efflux pumps extrude fluoroquinolones from the bacterial cell. A series of studies have identified the environment to be a reservoir of PMQR genes, with farm animals and aquatic habitats being significantly involved. In addition, the origin of the qnr genes has been identified, corresponding to the waterborne species Shewanella sp. Altogether, the recent observations suggest that the aquatic environment might constitute the original source of PMQR genes, that would secondly spread among animal or human isolates.

Plasmid-mediated quinolone resistance determinants qnr and aac(6')-Ib-cr in Escherichia coli and Klebsiella spp. from Norway and Sweden

The prevalence of the plasmid-mediated quinolone resistance genes qnr and aac(6')-Ib-cr was investigated among clinical isolates of Escherichia coli and Klebsiella spp. selected from 2 collections of consecutive isolates collected in 2004 to 2005 in Norway (n = 2479) and Sweden (n = 2980) and 1 group of extended-spectrum beta-lactamase (ESBL)-producing isolates collected in 2003 in Norway (n = 71). A total of 414 isolates was selected for screening based on resistance to nalidixic acid and/or reduced susceptibility/resistance to ciprofloxacin. The prevalence of both qnr and aac(6')-Ib-cr was higher among the ESBL producers (9.1% and 52.3%, respectively) than in the consecutive isolates (1.1% and 3.2%, respectively). qnrS1 was detected in 6 isolates, whereas qnrB1 and qnrB7 were detected in 2 isolates. The genetic structure surrounding qnrS1 was similar to previously described structures. In 2 isolates, qnrS1 was located on conjugative IncN-type plasmids of approximately 140 kb.

Plasmid-mediated quinolone resistance: a multifaceted threat

Although plasmid-mediated quinolone resistance (PMQR) was thought not to exist before its discovery in 1998, the past decade has seen an explosion of research characterizing this phenomenon. The best-described form of PMQR is determined by the qnr group of genes. These genes, likely originating in aquatic organisms, code for pentapeptide repeat proteins. These proteins reduce susceptibility to quinolones by protecting the complex of DNA and DNA gyrase or topoisomerase IV enzymes from the inhibitory effect of quinolones. Two additional PMQR mechanisms were recently described. aac(6')-Ib-cr encodes a variant aminoglycoside acetyltransferase with two amino acid alterations allowing it to inactivate ciprofloxacin through the acetylation of its piperazinyl substituent. oqxAB and qepA encode efflux pumps that extrude quinolones. All of these genes determine relatively small increases in the MICs of quinolones, but these changes are sufficient to facilitate the selection of mutants with higher levels of resistance. The contribution of these genes to the emergence of quinolone resistance is being actively investigated. Several factors suggest their importance in this process, including their increasing ubiquity, their association with other resistance elements, and their emergence simultaneous with the expansion of clinical quinolone resistance. Of concern, these genes are not yet being taken into account in resistance screening by clinical microbiology laboratories.

Detection of plasmid-mediated quinolone resistance genes in clinical isolates of Enterobacter spp. in Spain

We have studied by PCR and DNA sequencing the presence of the qnrA, qnrB, qnrS, aac(6')-Ib-cr, qepA, intI1, and ISCR1 genes in 200 clinical isolates of Enterobacter cloacae (n = 153) and E. aerogenes (n = 47) consecutively collected between January 2004 and October 2005 in two hospitals located in Santander (northern Spain) and Seville (southern Spain). Mutations in the quinolone resistance-determining region of gyrA and parC also were investigated in organisms containing plasmid-mediated quinolone resistance genes. The isolates had different resistant phenotypes, including AmpC hyperproduction, extended-spectrum beta-lactamase production, resistance or decreased susceptibility to quinolones, and/or resistance to aminoglycosides. Among the 116 E. cloacae isolates from Santander, qnrS1, qnrB5, qnrB2, and aac(6')-Ib-cr were detected in 22 (19%), 1 (0.9%), 1 (0.9%), and 3 (2.6%) isolates, respectively. Twenty-one, 17, and 2 qnrS1-positive isolates also contained bla(LAP-1), intI1, and ISCR1, respectively. A qnrB7-like gene was detected in one E. aerogenes isolate from Santander. No plasmid-mediated quinolone resistance gene was detected in the isolates from Seville. The qnrS1-containing isolates corresponded to four pulsed-field gel electrophoresis patterns and showed various levels of resistance to quinolones. Six isolates were susceptible to nalidixic acid and presented reduced susceptibility to ciprofloxacin. The qnrS1 gene was contained in a conjugative plasmid of ca. 110 kb, and when the plasmid was transferred to recipient strains that did not have a specific mechanism of quinolone resistance, the ciprofloxacin MICs ranged from 0.047 to 0.125 microg/ml.

New plasmid-mediated quinolone resistance gene, qnrC, found in a clinical isolate of Proteus mirabilis

Since the discovery of qnrA in 1998, two additional qnr genes, qnrB and qnrS, have been described. These three plasmid-mediated genes contribute to quinolone resistance in gram-negative pathogens worldwide. A clinical strain of Proteus mirabilis was isolated from an outpatient with a urinary tract infection and was susceptible to most antimicrobials but resistant to ampicillin, sulfamethoxazole, and trimethoprim. Plasmid pHS10, harbored by this strain, was transferred to azide-resistant Escherichia coli J53 by conjugation. A transconjugant with pHS10 had low-level quinolone resistance but was negative by PCR for the known qnr genes, aac(6')-Ib-cr and qepA. The ciprofloxacin MIC for the clinical strain and a J53/pHS10 transconjugant was 0.25 microg/ml, representing an increase of 32-fold relative to that for the recipient, J53. The plasmid was digested with HindIII, and a 4.4-kb DNA fragment containing the new gene was cloned into pUC18 and transformed into E. coli TOP10. Sequencing showed that the responsible 666-bp gene, designated qnrC, encoded a 221-amino-acid protein, QnrC, which shared 64%, 42%, 59%, and 43% amino acid identity with QnrA1, QnrB1, QnrS1, and QnrD, respectively. Upstream of qnrC there existed a new IS3 family insertion sequence, ISPmi1, which encoded a frameshifted transposase. qnrC could not be detected by PCR, however, in 2,020 strains of Enterobacteriaceae. A new quinolone resistance gene, qnrC, was thus characterized from plasmid pHS10 carried by a clinical isolate of P. mirabilis.

Characterization of plasmids harbouring qnrS1, qnrB2 and qnrB19 genes in Salmonella

OBJECTIVES

The aim of this study was to identify and characterize plasmids carrying qnrS1, qnrB2 and qnrB19 genes identified in Salmonella strains from The Netherlands. The identification of plasmids may help to follow the dissemination of these resistance genes in different countries and environments.

METHODS

Plasmids from 33 qnr-positive Salmonella strains were transferred to Escherichia coli and analysed by restriction, Southern blot hybridization, PCR and sequencing of resistance determinants. They were also assigned to incompatibility groups by PCR-based replicon typing, including three additional PCR assays for the IncU, IncR and ColE groups. The collection included isolates from humans and one from chicken meat.

RESULTS

Five IncN plasmids carrying qnrS1, qnrB2 and qnrB19 genes were identified in Salmonella enterica Bredeney, Typhimurium PT507, Kentucky and Saintpaul. qnrS1 genes were also located on three further plasmid types, belonging to the ColE (in Salmonella Corvallis and Anatum), IncR (in Salmonella Montevideo) and IncHI2 (in Salmonella Stanley) groups.

CONCLUSIONS

Multiple events of mobilization, transposition and replicon fusion generate the complexity observed in qnr-positive isolates that are emerging worldwide. Despite the fact that the occurrence of qnr genes in bacteria from animals is scarcely reported, these genes are associated with genetic elements and located on plasmids that are recurrent in animal isolates.

Unexpected occurrence of plasmid-mediated quinolone resistance determinants in environmental Aeromonas spp

We searched for plasmid-mediated quinolone resistance determinants of the Qnr type in several water samples collected at diverse locations from the Seine River (Paris, France). The qnrS2 genes were identified from Aeromonas punctata subsp. punctata and A. media. The qnrS2 gene was located on IncU-type plasmids in both isolates, which resulted in increased MIC values of quinolones and fluoroquinolones, once they were transferred into Escherichia coli. The qnrS2 gene identified in A. punctata was part of novel genetic structure corresponding to a mobile insertion cassette element. This identification of plasmid-mediated qnr genes outside Enterobacteriaceae underlines a possible diffusion of those resistance determinants within gram-negative rods.

Prevalence of qnr genes among extended-spectrum beta-lactamase-producing enterobacterial isolates in Barcelona, Spain

OBJECTIVES

To evaluate the presence of qnr genes among enterobacterial isolates carrying extended-spectrum beta-lactamases (ESBLs) in Barcelona, Spain.

METHODS

Screening for the qnrA, qnrB and qnrS genes was carried out by PCR amplification with specific primers in 305 non-duplicate, clinically relevant ESBL-producing enterobacterial isolates obtained from February 2003 to August 2004. ESBLs from all qnr-positive isolates were characterized by isoelectric focusing, PCR amplification and DNA sequencing. Plasmid analysis was performed by S1 digestion and hybridization with specific probes for the qnr and bla genes. Plasmids containing qnr genes were transferred by conjugation or transformation. The genetic environment of qnrA1 in selected isolates was characterized by cloning experiments.

RESULTS

Fifteen isolates, each from a different individual, carried qnr. Among them, 14 had qnrA1 (6 Klebsiella pneumoniae, 6 Enterobacter cloacae and 2 Escherichia coli isolates) and 1 had qnrS1 (K. pneumoniae). None of the isolates carried qnrB. Among the qnrA1-carrying isolates, 10 possessed both bla(CTX-M-9) and bla(SHV-12), 2 had both bla(CTX-M-9) and bla(SHV-92) and 2 had bla(CTX-M-9) alone. The isolate with qnrS1 possessed bla(SHV-12). The qnrA1 and ESBL genes were located together on plasmids ranging in size from 40 to 320 kb. qnrS1 and bla(SHV-12) were not located on the same plasmid. Transfer of quinolone resistance was successfully achieved from all but three isolates. The cloned region surrounding qnrA in two K. pneumoniae isolates revealed a novel genetic organization.

CONCLUSIONS

The prevalence of qnr among enterobacterial clinical isolates carrying ESBLs between 2003 and 2004 in Barcelona was 4.9%. qnrA1 was the most prevalent, whereas only one qnrS and no qnrB were detected.

Plasmid-mediated quinolone resistance conferred by qnrS1 in Salmonella enterica serovar Virchow isolated from Turkish food of avian origin

OBJECTIVES

To study the molecular characteristics of the quinolone and associated ampicillin resistance mechanisms present in Salmonella enterica serovar Virchow isolated from Turkish foods.

METHODS

Nine epidemiologically unrelated Salmonella Virchow strains isolated from foods (chicken and minced meat) sold in different markets in Ankara were analysed for their susceptibility to 17 antimicrobials. The strains were typed by PFGE and plasmid profiling and investigated by molecular methods (PCR/sequencing) for the presence of several resistance genes, class 1 integrons and mutations in the quinolone resistance-determining regions. Plasmids conferring quinolone resistance were analysed by restriction fragment length polymorphism (RFLP) analysis, DNA hybridization, sequencing, replicon-typing PCR and mating experiments.

RESULTS

All strains showed nalidixic acid resistance (MIC >or= 128 mg/L) together with a decreased susceptibility to ciprofloxacin (three strains with an MIC of 1 mg/L and six with an MIC of 0.25 mg/L), associated with mutations within the gyrA gene (Asp-87 --> Tyr-87). In three strains, qnrS1 genes were detected. Ampicillin resistance encoded by a bla(CTX-M3) gene and/or bla(TEM-1-like) gene was found in four strains. Three of these strains carried an approximately 45 kb conjugative plasmid, designated pRQ2006, harbouring qnrS1 and a Tn3-like transposon. Partial sequencing and RFLP of pRQ2006 indicated its similarity to the qnrS1 plasmid pAH03786 found in a Japanese Shigella flexneri 2b isolate.

CONCLUSIONS

This is the first study describing the presence of qnrS1 genes in bacterial isolates from Turkey. The pRQ2006 plasmid seems to be more related to the S. flexneri 2b qnrS1 plasmid pAH0376 than to the Salmonella qnrS1-carrying plasmids pINF5 and TPqnrS-2.

Identification of the novel narrow-spectrum beta-lactamase SCO-1 in Acinetobacter spp. from Argentina

By studying the beta-lactamase content of several Acinetobacter spp. isolates from Argentina, producing the expanded-spectrum beta-lactamases (ESBL) VEB-1a or PER-2, a novel Ambler class A beta-lactamase gene was identified. It encoded the narrow-spectrum beta-lactamase SCO-1, whose activity was inhibited by clavulanic acid. SCO-1 hydrolyzes penicillins at a high level and cephalosporins and carbapenems at a very low level. beta-Lactamase SCO-1 was identified from unrelated VEB-1a-positive or PER-2-positive Acinetobacter spp. isolates recovered from three hospitals. The bla(SCO-1) gene was apparently located on a plasmid of ca. 150 kb from all cases but was not associated with any ESBL-encoding gene. The G+C content of the bla(SCO) gene was 52%, a value that does not correspond to that of the A. baumannii genome (39%). beta-Lactamase SCO-1 shares 47% amino acid identity with CARB-5 and ca. 40% with the enzymes TEM, SHV, and CTX-M. A gene encoding a putative resolvase was identified downstream of the bla(SCO-1) gene, but its precise way of acquisition remains to be determined.