Showing papers on "Quinolone published in 2010"

Structural basis of quinolone inhibition of type IIA topoisomerases and target-mediated resistance

Abstract: Quinolone antibacterials have been used to treat bacterial infections for over 40 years. A crystal structure of moxifloxacin in complex with Acinetobacter baumannii topoisomerase IV now shows the wedge-shaped quinolone stacking between base pairs at the DNA cleavage site and binding conserved residues in the DNA cleavage domain through chelation of a noncatalytic magnesium ion. This provides a molecular basis for the quinolone inhibition mechanism, resistance mutations and invariant quinolone antibacterial structural features.

Structural insights into the quinolone resistance mechanism of Mycobacterium tuberculosis DNA gyrase.

Abstract: Mycobacterium tuberculosis DNA gyrase, an indispensable nanomachine involved in the regulation of DNA topology, is the only type II topoisomerase present in this organism and is hence the sole target for quinolone action, a crucial drug active against multidrug-resistant tuberculosis. To understand at an atomic level the quinolone resistance mechanism, which emerges in extensively drug resistant tuberculosis, we performed combined functional, biophysical and structural studies of the two individual domains constituting the catalytic DNA gyrase reaction core, namely the Toprim and the breakage-reunion domains. This allowed us to produce a model of the catalytic reaction core in complex with DNA and a quinolone molecule, identifying original mechanistic properties of quinolone binding and clarifying the relationships between amino acid mutations and resistance phenotype of M. tuberculosis DNA gyrase. These results are compatible with our previous studies on quinolone resistance. Interestingly, the structure of the entire breakage-reunion domain revealed a new interaction, in which the Quinolone-Binding Pocket (QBP) is blocked by the N-terminal helix of a symmetry-related molecule. This interaction provides useful starting points for designing peptide based inhibitors that target DNA gyrase to prevent its binding to DNA.

Voreloxin is an anticancer quinolone derivative that intercalates DNA and poisons topoisomerase II

Abstract: Background Topoisomerase II is critical for DNA replication, transcription and chromosome segregation and is a well validated target of anti-neoplastic drugs including the anthracyclines and epipodophyllotoxins. However, these drugs are limited by common tumor resistance mechanisms and side-effect profiles. Novel topoisomerase II-targeting agents may benefit patients who prove resistant to currently available topoisomerase II-targeting drugs or encounter unacceptable toxicities. Voreloxin is an anticancer quinolone derivative, a chemical scaffold not used previously for cancer treatment. Voreloxin is completing Phase 2 clinical trials in acute myeloid leukemia and platinum-resistant ovarian cancer. This study defined voreloxin's anticancer mechanism of action as a critical component of rational clinical development informed by translational research. Methods/Principal Findings Biochemical and cell-based studies established that voreloxin intercalates DNA and poisons topoisomerase II, causing DNA double-strand breaks, G2 arrest, and apoptosis. Voreloxin is differentiated both structurally and mechanistically from other topoisomerase II poisons currently in use as chemotherapeutics. In cell-based studies, voreloxin poisoned topoisomerase II and caused dose-dependent, site-selective DNA fragmentation analogous to that of quinolone antibacterials in prokaryotes; in contrast etoposide, the nonintercalating epipodophyllotoxin topoisomerase II poison, caused extensive DNA fragmentation. Etoposide's activity was highly dependent on topoisomerase II while voreloxin and the intercalating anthracycline topoisomerase II poison, doxorubicin, had comparable dependence on this enzyme for inducing G2 arrest. Mechanistic interrogation with voreloxin analogs revealed that intercalation is required for voreloxin's activity; a nonintercalating analog did not inhibit proliferation or induce G2 arrest, while an analog with enhanced intercalation was 9.5-fold more potent. Conclusions/Significance As a first-in-class anticancer quinolone derivative, voreloxin is a toposiomerase II-targeting agent with a unique mechanistic signature. A detailed understanding of voreloxin's molecular mechanism, in combination with its evolving clinical profile, may advance our understanding of structure-activity relationships to develop safer and more effective topoisomerase II-targeted therapies for the treatment of cancer.

Transferable Quinolone Resistance in Vibrio cholerae

Abstract: Ciprofloxacin was introduced for treatment of patients with cholera in Bangladesh because of resistance to other agents, but its utility has been compromised by the decreasing ciprofloxacin susceptibility of Vibrio cholerae over time. We correlated levels of susceptibility and temporal patterns with the occurrence of mutation in gyrA, which encodes a subunit of DNA gyrase, followed by mutation in parC, which encodes a subunit of DNA topoisomerase IV. We found that ciprofloxacin activity was more recently further compromised in strains containing qnrVC3, which encodes a pentapeptide repeat protein of the Qnr subfamily, members of which protect topoisomerases from quinolone action. We show that qnrVC3 confers transferable low-level quinolone resistance and is present within a member of the SXT integrating conjugative element family found commonly on the chromosomes of multidrug-resistant strains of V. cholerae and on the chromosomes of Escherichia coli transconjugants constructed in the laboratory. Thus, progressive increases in quinolone resistance in V. cholerae are linked to cumulative mutations in quinolone targets and most recently to a qnr gene on a mobile multidrug resistance element, resulting in further challenges for the antimicrobial therapy of cholera.

Comparative In Vitro Activities of Nemonoxacin (TG-873870), a Novel Nonfluorinated Quinolone, and Other Quinolones against Clinical Isolates

Abstract: The in vitro antibacterial activities of nemonoxacin (TG-873870), a novel nonfluorinated quinolone, against 770 clinical isolates were investigated. Nemonoxacin (tested as its malate salt, TG-875649) showed better in vitro activity than ciprofloxacin and levofloxacin against different species of staphylococci, streptococci, and enterococci, Neisseria gonorrhoeae, and Haemophilus influenzae. The in vitro activity of TG-875649 was also comparable to or better than that of moxifloxacin against these pathogens, which included ciprofloxacin-resistant, methicillin-resistant Staphylococcus aureus and levofloxacin-resistant Streptococcus pneumoniae.

Prevalence of mechanisms decreasing quinolone-susceptibility among Salmonella spp. clinical isolates

Abstract: Fluoroquinolone treatment failure has been reported in patients with nalidixic acid-resistant Salmonella infections. Both chromosomal- and plasmid-mediated quinolone-resistance mechanisms have been described. The objective of this study was to identify the prevalence of these mechanisms in a collection of 41 Salmonella spp. clinical isolates causing acute gastroenteritis, obtained in the Hospital Clinic, Barcelona. The minimum inhibitory concentrations (MICs) of nalidixic acid and ciprofloxacin were determined by Etest. Mutations in the quinolone-resistance determining regions (QRDRs) of the gyrA, gyrB, and parC genes and the presence of the qnr, aac(6')-Ib-cr, and qepA genes were detected by PCR and DNA sequencing. All isolates showed constitutive expression of an efflux pump. None of the isolates were ciprofloxacin-resistant, whereas 41.5% showed nalidixic acid resistance associated with a mutation in gyrA and overexpression of an efflux pump. Although qnrS1, qnrB6, and qepA were found in four isolates, the expression of these genes was not associated with decreased quinolone susceptibility. Mutations in the gyrA gene and overexpression of an efflux pump were critical for nalidixic acid resistance and decreased susceptibility to ciprofloxacin in these isolates. However, plasmid-mediated quinolone resistance did not seem to play a major role. To our knowledge, this is the first description of qepA in Salmonella.

Bactericidal activity of besifloxacin against staphylococci, Streptococcus pneumoniae and Haemophilus influenzae

Abstract: Objectives: Besifloxacin is a novel fluoroquinolone that was recently approved for topical treatment of bacterial conjunctivitis. The compound was shown to be active in vitro against a broad spectrum of bacteria, including isolates resistant to other antibacterials. Here, the bactericidal activity of besifloxacin was evaluated against the most common bacterial conjunctivitis pathogens. Methods: MIC, MBC and time-kill experiments with besifloxacin and comparators were performed according to CLSI guidelines. Quinolone resistance-determining regions (QRDRs) were sequenced using standard PCR-based techniques. Results: MIC and MBC data indicated that besifloxacin was the most potent fluoroquinolone tested against Staphylococcus aureus (n=30), Staphylococcus epidermidis (n= 15 ) and Streptococcus pneumoniae (n=35), while all fluoroquinolones were highly active against Haemophilus influenzae (n=40). Besifloxacin MBC:MIC ratios were <4 for 97.5% of all isolates tested (n=120). All fluoroquinolones tested, as well as tobramycin, were bactericidal, while azithromycin was bactericidal against S. pneumoniae and H. influenzae, but bacteriostatic against the staphylococci. Time-kill assays with all four species showed that besifloxacin caused ≥1000-fold killing within 2 h for 11 of 12 isolates. Only one isolate treated with moxifloxacin and three ciprofloxacin-treated isolates achieved the same level of bactericidal activity under the same conditions. Unlike the comparator fluoroquinolones, besifloxacin maintained a high potency and bactericidal activity even against strains that contained multiple mutations in the genes encoding DNA gyrase and topoisomerase IV. Conclusions: Overall, besifloxacin demonstrated rapid bactericidal activity against the four major human pathogens tested here, including isolates that showed in vitro resistance to other fluoroquinolones, β-lactams, macrolides or aminoglycosides.

From 6-aminoquinolone antibacterials to 6-amino-7-thiopyranopyridinylquinolone ethyl esters as inhibitors of Staphylococcus aureus multidrug efflux pumps.

Abstract: The thiopyranopyridine moiety was synthesized as a new heterocyclic base to be inserted at the C-7 position of selected quinolone nuclei followed by a determination of antibacterial activity against strains of Staphylococcus aureus. Selected thiopyranopyridinylquinolones showed significant antimicrobial activity, including strains having mutations in gyrA and grlA as well as other strains overexpressing the NorA multidrug (MDR) efflux pump. Most derivatives did not appear to be NorA substrates. The effect of the thiopyranopyridinyl substituent on making these quinolones poor substrates for NorA was investigated further. Several quinolone ester intermediates, devoid of any intrinsic antibacterial activity, were tested for their abilities to inhibit the activities of NorA (MFS family) and MepA (MATE family) S. aureus MDR efflux pumps. Selected quinolone esters were capable of inhibiting both MDR pumps more efficiently than the reference compound reserpine. Moreover, they also were able to restore, and even ...

Quinolone-resistant Salmonella Typhi in South Africa, 2003–2007

Abstract: In South Africa, for the years 2003-2007, the Enteric Diseases Reference Unit received 510 human isolates of Salmonella Typhi, of which 27 were nalidixic acid-resistant [minimum inhibitory concentrations (MICs) 128-512 microg/ml] with reduced susceptibility to ciprofloxacin (MICs 0.125-0.5 microg/ml). Pulsed-field gel electrophoresis analysis of 19 available isolates differentiated them into five DNA pattern types; multiple-locus variable-number tandem repeat analysis differentiated the isolates into 10 types. This level of genetic diversity suggested that resistant strains usually emerged independently of one another. A 16- to 32-fold decrease in nalidixic acid MIC and a 2- to 8-fold decrease in ciprofloxacin MIC, was observed in the presence of an efflux pump inhibitor. All isolates were negative by PCR screening for qnr genes. Seven resistant isolates were further analysed for mutations in the quinolone resistance-determining region of gyrA, gyrB, parC and parE. No amino-acid mutations were identified in GyrB and ParE; all isolates showed amino-acid mutations in both GyrA and ParC. We conclude that amino-acid mutations in GyrA and ParC in combination with active efflux of antibiotic out of the bacterial cell are the probable mechanisms conferring quinolone resistance.

Study of Mutations in the DNA gyrase gyrA Gene of Escherichia coli

Abstract: Quinolones are a large and widely consumed class of synthetic drugs. Expanded-spectrum quinolones, like ciprofloxacin are highly effective against Gram-negative bacteria, especially Escherichia coli. In E. coli the major target for quinolones is DNA gyrase. This enzyme is composed of two subunits, GyrA and GyrB encoding by gyrA and gyrB, respectively. Mutations in either of these genes cause quinolone resistance. Mutations in QRDR section of gyrA are more common in quinolone resistant clinical isolates. However, a mutation outside of this region was also reported. Thus, this study was aimed to provide more information on mutations sites in gyrA. For this purpose, spontaneous ciprofloxacin resistant mutants arisen in cultures of E. coli ATCC 25922 and MG1655 were isolated on LB agar containing ciprofloxacin. Next, the MICs of these clones were measured and the presence of mutation in gyrA was investigated. Results showed that the frequency of ciprofloxacin resistant mutants in cultures of E. coli strains was low. However, these mutants had different MICs, depending on the day of isolation. Most of ciprofloxacin-resistant mutants possess mutations in QRDR region and precisely at Ser-83. However, mutations outside of this region were also found at Tyr-50 and Ala-119. In conclusion, the presence of mutations at amino acids 50 and 119 suggests that in addition to QRDR section and Tyr-122, these sites are also essential for DNA gyrase activity.

In Vitro Antituberculosis Activities of ACH-702, a Novel Isothiazoloquinolone, against Quinolone-Susceptible and Quinolone-Resistant Isolates

Abstract: ACH-702 is a new isothiazoloquinolone with potent in vitro and in vivo activities against important bacterial pathogens, including Staphylococcus aureus. In this study, ACH-702 was found to have promising in vitro antibacterial activity against Mycobacterium tuberculosis, with MICs of ≤1 μg/ml, comparable to that of the fluoroquinolone moxifloxacin for quinolone-susceptible isolates but superior to that for quinolone-resistant isolates. Biochemical assays involving M. tuberculosis gyrase enzymes indicated that ACH-702 had significantly improved inhibitory activity compared with fluoroquinolones.

Genomewide Screening for Novel Genetic Variations Associated with Ciprofloxacin Resistance in Bacillus anthracis

Abstract: Fluoroquinolone (FQ) resistance of Bacillus anthracis is a serious concern in the fields of biodefense and bioterrorism since FQs are very effective antibiotics and are recommended as first-line treatment against this lethal bacterium In this study, we obtained 2 strains of B anthracis showing resistance or intermediate resistance to ciprofloxacin (CIP) by a stepwise selection procedure with increasing CIP concentrations Fifteen genetic variations were identified between the parental and CIP-resistant strains by next-generation sequencing Nonsynonymous mutations in the quinolone resistance-determining region (QRDR) of type II DNA topoisomerase were identified in the resistant strain but not in the intermediate-resistant strain The GBAA0834 (TetR-type transcriptional regulator) locus was also revealed to be a novel “mutation hot spot” that leads to the increased expression of multidrug efflux systems for CIP resistance As an initial step of CIP resistance in B anthracis, such disruptive mutations of GBAA0834 appear to be more easily acquired than those in an essential gene, such as that encoding type II DNA topoisomerase Such an intermediate-resistant phenotype could increase a cell population under CIP-selective pressure and might promote the emergence of highly resistant isolates Our findings reveal, in addition to QRDR, crucial genetic targets for the investigation of intermediate resistance of B anthracis to FQs

Novel Variants of the qnrB Gene, qnrB22 and qnrB23, in Citrobacter werkmanii and Citrobacter freundii

Abstract: Resistance to quinolones in Gram-negative bacteria is usually mediated by the following: (i) chromosomal mutations that alter the target enzymes, DNA gyrase and topoisomerase IV, in their quinolone resistance-determining regions (QRDR), (ii) changes in drug entry (loss of porin channels), and (iii) the presence of plasmid-mediated quinolone resistance (PMQR) determinants [qnrA, qnrB, qnrS, qnrC, and qnrD, coding for Qnr proteins that protect DNA gyrase from quinolone attack; aac(6′)-Ib-cr, coding for a protein that acetylates quinolones; and qepA, coding for a quinolone efflux pump] (2, 12). The recent worldwide emergence of PMQR due to the qnr and aac(6′)-Ib-cr genes is a concerning fact among human and animal Gram-negative pathogens (8). The aim of this study was to determine the prevalence of qnr genes among 93 consecutive nonrepetitive Enterobacteriaceae of animal origin and to characterize positive isolates. These isolates were collected from chickens (n = 37) and pigs (n = 56) at five farms near the city of Seoul (South Korea) in 2007. The presence of PMQR determinants and QRDR mutations was investigated by PCR-based detection and sequencing (2, 5, 6). The qnrA, qnrS, qnrC, qnrD, aac(6′)-Ib-cr, and qepA genes were not found. Two isolates (2.2%) were found to carry qnr-like genes (Citrobacter werkmanii PS012 and Citrobacter freundii S008). Sequence analysis identified two novel qnrB variants, qnrB22 and qnrB23, in C. werkmanii PS012 (isolated from a pig at the Daeyoung Farm) and C. freundii S008 (isolated from a chicken at the Hanmi Farm), respectively. These new variants were assigned according to the qnr numbering scheme shown in the Lahey website (http://www.lahey.org/qnrStudies). The qnrB22 gene had 99.7% nucleotide identity with qnrB4. The qnrB23 gene had 99.9% nucleotide identity with qnrB9. The deduced QnrB22 product had two amino acid substitutions (Ser36Cys and Gly188Val) compared with the amino acid sequence of QnrB4. Compared with the amino acid sequence of QnrB9, QnrB23 showed one amino acid substitution (Asn27Tyr). C. werkmanii PS012 showed a reduced susceptibility (MIC > 0.125 μg/ml) to fluoroquinolones (ofloxacin, norfloxacin, levofloxacin, and ciprofloxacin) (Table ​(Table1).1). C. freundii S008 was nonsusceptible (resistant or intermediate) to the fluoroquinolones (Table ​(Table1).1). The MICs were determined by E-test (AB Biodisk, Solna, Sweden) and interpreted according to Clinical and Laboratory Standards Institute guidelines (4). The QRDR mutations associated with fluoroquinolone resistance were not detected in the two isolates (Table ​(Table11). TABLE 1. Characteristics of the two Citrobacter isolates, their transconjugants, Escherichia coli DH5α transformants, and reference (recipient or host) strains The transfer of qnrB22- and qnrB23-harboring plasmids to Escherichia coli J53 AzideR was accomplished through mating experiments described previously (9). Transconjugants were selected on Mueller-Hinton agar plates containing sodium azide (150 μg/ml) and ciprofloxacin (0.125 μg/ml). Fluoroquinolone (or nalidixic acid) MICs of the two transconjugants (TrcPS012 and TrcS008) were similar to those of the donor strains (Table ​(Table1).1). Strain TrcS008, carrying qnrB23, had MIC values for nalidixic acid and fluoroquinolones that were higher than those of TrcPS012, harboring qnrB22 (Table ​(Table11). The PCR amplicons of the qnrB22 and qnrB23 genes were cloned into the vector pCR-BluntII-TOPO and transformed into the E. coli DH5α host strain (Invitrogen, Karlsruhe, Germany). Primers used were as follows: for cloning of qnrB22, 5′-ATGACTCTGGCGTTAGTTGG-3′ and 5′-TTAACCCATGACAGCGATACCAA-3′; and for cloning of qnrB23, 5′-ATGACGCCATTACTGTATAAAAAAACA-3′ and 5′-CTAGCCAATAATCGCGATGCC-3′. A decrease in quinolone susceptibility was observed with both transformants, even though the qnrB23-carrying transformant showed higher MICs than that carrying qnrB22 (Table ​(Table1).1). Fluoroquinolone (or nalidixic acid) MICs of two transformants (TrfPS012 and TrfS008) were lower than those of two transconjugants (TrcPS012 and TrcS008), which was compatible with a recent finding (11). The differences observed between transconjugants and transformants might be related to recipient susceptibility (E. coli DH5α was more susceptible than E. coli J53 AzideR), plasmid copy number, and/or the presence of additional PMQR determinants in the two plasmids. The conjugative plasmids of C. werkmanii PS012 and C. freundii S008 showed identical patterns (showing 13 distinct bands) and similar molecular sizes (about 23 kb) in restriction fragment length polymorphism analysis after digestion with BglII, as described previously (1). qnrB22- and qnrB23-harboring plasmids belonged to an incompatibility group, IncL/M, according to a PCR-based replicon-typing scheme (3). These results suggest that conjugative IncL/M plasmids might play a role in the dissemination and evolution of qnrB genes. The association of various antibiotic resistance genes, including PMQR determinants with conjugative IncL/M plasmids from human isolates of the Enterobacteriaceae, has been described in several reports (7, 10, 13, 14). Despite the currently low prevalence (2.2%) of qnrB22 and qnrB23, surveillance for bacterial isolates carrying these resistance determinants in animals is warranted.

Molecular mechanisms of quinolone resistance in clinical isolates of Aeromonas caviae and Aeromonas veronii bv. sobria.

Abstract: Mutations in quinolone targets were studied together with quinolone efflux pump activation and plasmid-mediated quinolone resistance determinants in nalidixic-acid-resistant isolates of Aeromonas caviae and Aeromonas veronii . Among 135 clinical Aeromonas spp . isolated from stools of patients with gastrointestinal symptoms, 40 nalidixic acid-resistant strains belonging to A. caviae and A. veronii were selected and their susceptibility to different quinolones (ciprofloxacin, norfloxacin, ofloxacin) further evaluated. Susceptibility to nalidixic acid and ciprofloxacin in the presence/absence of Phe- Arg-β-naphthylamide was also determined. The 16 nalidixic-acid-resistant strains identified as A. caviae were more resistant than the 24 A. veronii bv. sobria strains to ciprofloxacin, norfloxacin, and ofloxacin. All strains showed a mutation (single or double) at position 83 of the QRDR sequence of gyrA, with Ser-83 → Ile as the most frequent substitution. By contrast, no mutations were found at position 87 of gyrA. Double substitutions (GyrA-ParC) were detected in 50% of A. veronii bv. sobria isolates and in 43.75% of A. caviae strains. Both species showed decreases in the MICs of ciprofloxacin. A qnrS gene was found in an A. caviae strain. Thus, in the two species of nalidixic-acid-resistant Aeromonas isolates examined, resistance mediated by efflux pumps contributed only slightly to ciprofloxacin resistance. While two isolates were positive for the aac(6′)-Ib gene, no -cr variants were detected. [ Int Microbiol 2010; 13(3):135-141]

Extended spectrum of quinolone resistance, even to a potential latter third-generation agent, as a result of a minimum of two GrlA and two GyrA alterations in quinolone-resistant Staphylococcus aureus.

Abstract: Background: This study was performed to determine the extended spectrum of quinolone resistance caused by increased mutations within the target enzymes of quinolones. Metho

Neisseria meningitidis with reduced susceptibility to quinolones in Singapore

Abstract: Sir, Ciprofloxacin is commonly prescribed as a single-dose chemoprophylactic agent for close contacts of patients with meningococcal infection. Neisseria meningitidis with reduced susceptibility to fluoroquinolones has recently emerged, with sporadic cases reported in France, Australia, Argentina, Spain, Hong Kong and Israel. Recently an outbreak of serogroup A emerged in India, and a cluster of three cases of serogroup B in the USA. To our knowledge, failure of ciprofloxacin prophylaxis due to quinolone resistance has not been reported To date, reduced susceptibility to fluoroquinolones in meningococci has remained rare, with 10 unrelated strains found in an analysis of 5300 isolates in Spain, and only 3 from .5000 isolates in France. Most mutations have arisen in GyrA. However, mutations have also been detected in GyrB and ParE, although their significance remains uncertain. In addition, in vitro changes have been induced in ParC and resistance to quinolones has also been reported through an efflux mechanism. – 4 Following the isolation of N. meningitidis with reduced susceptibility to ciprofloxacin from a 36-year-old man with meningitis in 2008, all stored viable clinical isolates from Singapore’s three largest hospitals (Tan Tock Seng, Singapore General and National University hospitals) were screened for reduced susceptibility to nalidixic acid and rifampicin by disc diffusion, using the CLSI guidelines. Ciprofloxacin MICs were determined by agar plate dilution for isolates with reduced susceptibility to nalidixic acid, using the Australian Gonococcal Surveillance Programme (AGSP) guidelines. MICs obtained with this method give identical results for identical GyrA changes in Neisseria gonorrhoeae and N. meningitidis. All isolates for which the MIC is .0.03 mg/L either have changes in the quinolone resistance determining region (QRDR) or an increased efflux of quinolones, while those for which the MIC is ,0.03 mg/L do not. In the absence of clinical correlation data, an MIC of .0.03 mg/L is taken to indicate reduced susceptibility by both the AGSP and CLSI methods. Multilocus sequence typing (MLST) was carried out using protocols available on the Neisseria MLST website. To characterize the mechanisms of resistance to ciprofloxacin, we sequenced the QRDRs of GyrA, GyrB, ParC and ParE of isolates with a ciprofloxacin MIC of .0.03 mg/L. Penicillin MICs were determined with Etests (AB BIODISK, Solna, Sweden) for all isolates, using Mueller–Hinton agar with 5% sheep blood and interpreted according to CLSI criteria for agar dilution. Of 75 isolates collected between 2000 and 2008, two (3%) were resistant to nalidixic acid, a Group C isolate from 2008 and a Group B isolate from 2002. Both isolates had a raised ciprofloxacin MIC of 0.25 mg/L. All 75 isolates were susceptible to rifampicin. There were 13 isolates (17%) intermediate and 2 (3%) resistant to penicillin (MICs of 0.38 and 0.47 mg/L). MLST confirmed that the two isolates with reduced quinolone susceptibility were unrelated. The 2008 isolate was identified as sequence type (ST)-4821. The 2002 isolate was a new ST with alleles 4, 10, 76, 71, 13, 2, 75 although the aroE allele had one nucleotide different from allele 76 (C to T at position 39). The 2008 ST-4821 isolate had the most common GyrA substitution of threonine to isoleucine at position 91. The 2002 isolate had three mutations detected in GyrA: Thr91!Val; Asn103!Asp; and Ala105!Ser. To our knowledge, the Thr91!Val substitution has not been previously described in N. meningitidis. Neither of the isolates had changes in GyrB, ParC or ParE. Similarities in the mechanism of quinolone resistance in meningococci and gonococci, have prompted concerns that resistance will climb to mirror that of gonococci. Resistance to quinolones among N. gonorrhoeae is now so common that use of ciprofloxacin for the treatment of gonorrhoea is no longer recommended by the US Centers for Disease Control and Prevention. In Singapore, ciprofloxacin resistance among gonococci reached an alarming 61.8% in 2006 (74% in 2008; A. L. Tan, unpublished data). Ciprofloxacin is a prescription-only medicine in Singapore, but is in widespread use. An outbreak of meningococcal meningitis with reduced susceptibility to quinolones has already been seen in India in 2005, a country with liberal use of ciprofloxacin. Although our data are from small numbers, as meningococcal infections are uncommon in Singapore (usually ,10 cases per year), the 3% rate of quinolone resistance in this study is remarkably high when compared with other reports. Surveillance for reduced susceptibility and judicious quinolone use is forever increasing in importance but our local resistance data for the related N. gonorrhoeae may suggest the future is already written.

Synthesis of New 7-chloro-8-substituted-1,4-dihydro-4-oxo-quinolin- 3-carboxylic Acids

Abstract: Fig. 2. The structure of the new compounds R1 = ethyl, isopropyl, R8 = methyl; chlor Fig. 3. 8MeQE 4-Oxo-quinolin-3-carboxylic acid are characterized by a more rapid bactericidal activity and a much wider antibacterial spectrum. They are active both in Gramnegative and the Gram-positive, but also the recently discovered intracellular growing germs (Legionella, Mycoplasma, etc.), or even acid-resistant bacilli (M. tuberculosis and M. leprae) [1-5]. Scope of quinolone use has extended widely from urinary tract infections in acute and chronic systemic infections (lung infections, osteoarticular, septicemia and endocarditis, chronic infections (chronic bronchitis, purulent osteoarthritis, chronic prostatitis, cystitis and chronic sinusitis). Front antibiotics βlactam (penicillins, cephalosporins) has the advantage of good digestive absorption allowing the possibility of performing treatment with oral administration of parental avoidance. 4-Oxo-quinolin-3-carboxylic acid derivatives is an important class of antibacterial agents with wide action. Basic structure of these compounds (fig. 1) is a bicyclic structure, which contains a ring of type A 4-piridinona combined with aromatic or heteroaromatic ring B. The ring type A 4piridinona is a ring with absolute necessity: an unsaturation in position 2-3; a free acid function in position 3; a substituent at nitrogen in position 1.

Characterization of quinolone resistance in Escherichia coli strains of animal origin from Italy.

Abstract: The aim of this study was to assess the possible circulation of genetic resistance determinants and chromosomal point mutations in quinolone-resistant Escherichia coli isolated from livestock from central Italy Forty-nine E coli isolates were recovered from animals during the surveillance activities of the Istituto Zooprofilattico Abruzzo e Molise (IZSA&M), Italy, over 2 years The plasmid resistance determinants and point mutations in DNA gyrase and topoisomerase IV were characterized by PCR and DNA sequencing Of the 49 E coli isolates, 34 were resistant to nalidixic acid, 4 to ciprofloxacin and 11 to nalidixic acid, ciprofloxacin and enrofloxacin Chromosomal point mutations were found in gyrA gene (Ser83Leu and Asp87Asn) and gyrB (Gln434His, Lys444Arg and Gly435Val) We also report the simultaneous presence of qnrS1 quinolone resistance determinant, dfrA1-aadA22 gene cassettes and amino acid substitution Ser83Leu in the gyrA gene in an E coli strain resistant only to nalidixic acid

Characterization of Mutations in DNA Gyrase and Topoisomerase IV Involved in Quinolone Resistance of Clinical Mycoplasma gallisepticum Isolates

Abstract: Susceptibilities of 4 isolated M.gallisepticum to common used antimicrobials were determined by broth dilution method.PCR and sequencing were applied for analysis of quinolone resistance-determining regions of the four target genes encoding DNA gyrase and topoisomerase Ⅳ from 4 isolates.The results showed that 4 isolates presented higher susceptible to tylosin,tiamulin,valnemulin and tilmicosin,moderate susceptible to tetracycline and erythromycin,and resistant to lincomycin,florfenicol and 3 fluroquinolone drugs to a certain extent.Several mutations were found in the two fluoroquinolone targets GyrA and ParC.Double mutations within QRDR of GyrA were found among 4 isolated M.gallisepticum,with the same substitution patterns of Ser81→Gly and Ser83→Ile.There was only one alteration existed within QRDR of ParC(Ser80→Leu) among 4 isolates.No mutations were found within QRDR of GyrB and ParE in 4 isolates.

Mechanisms of quinolone resistance and implications for human and animal health.

Abstract: Quinolone antibiotics have been widely used in human and veterinary medicine. This has caused the development of resistance and difficulties in the treatment of complicated bacterial infections in humans. The resistance to quinolones develops due to chromosome mutations and it can also be transferred by plasmids. The target enzyme for quinolones in Gram-negative bacteria is Gyrasa A, while the target enzyme in Grampositive bacteria is mostly topoisomerase IV. Gyrase A consists of two subunits encoded by genes gyrA and gyrB. The function of the enzyme is to introduce negative super coiling in DNA and therefore is essential for the replication of bacteria. Quinolone resistance develops if point mutations at 83 and/or 87 codon are introduced on gyrA. Establishing a minimal inhibitory concentration (MIC) to this group of antimicrobials will reveal possible mutations. Recently it was discovered that quinolone resistance is transmittable by plasmid termed PMQR (plasmid mediated quinolone resistance). The target gene marked qnr encodes a pentapeptide repeat family protein. Pentapeptide repeats form sheets, involved in protein-protein interactions. Qnr protein binds to GyrA protecting the enzyme from the inhibitory effect of ciprofloxacin. The distribution of qnr related resistance is higher in humans than in animals. In poultry, however, this type of resistance is present more than in other animals. Plasmid mediated resistance contributes to the faster spread of quinolone resistance. Proper food handling will significantly contribute to decreasing the risk from infection to which people are exposed. In medical and veterinary laboratories antimicrobial resistance monitoring in clinical and environmental isolates is advised. Since correlation between antibiotics application and antimicrobial resistance is often suggested, antimicrobial use must be under strict control of the authorities both in human and in veterinary medicine. .

Vancomycin minimal inhibitory concentration from broth microdilution and Etest in respiratory tract samples of patients with ventilation-associated pneumonia

Abstract: additive effect on quinolone susceptibility.7 Though Qnr proteins and Aac(60)-Ib-cr only induce low level quinolone resistance, they are known to facilitate selection of resistancemutations in the presence of concentrations of quinolone antibiotics.8 We describe an isolate of K. pneumoniae isolate carrying three plasmid-mediated quinolone-resistant genes (qnrB, qnrS and aac (60)-Ib-cr variant) together with a novel variant of gyrA gene that has not been reported previously. These mechanisms were likely to have contributed individually to the high level ciprofloxacin and levofloxacin resistance.