Type II topoisomerase mutations in clinical isolates of Enterobacter cloacae and other enterobacterial species harbouring the qnrA gene

The qnr genes are transferable genes that confer low-level quinolone resistance by protection of topoisomerase. The occurrence of mutations in DNA gyrase (gyrA, gyrB) and topoisomerase IV (parC, parE) genes in strains harbouring qnr was investigated in 28 qnrA-positive clinical isolates, among which 7 strains also harboured qnrS. Topoisomerase mutations were found in 25 (89%) of the 28 strains, with at least two mutations (gyrA and parC) in 13 strains and one mutation in 12 strains. Isolates of the Enterobacter cloacae complex were compared with reference strains of the new Enterobacter species. gyrA mutations were found at position 83 (Ser or Thr for Ile, Tyr, Leu or Phe depending on the species), and new gyrB mutations were described (S463A, S464F). qnrA had an additive effect of a 10-fold increase in the minimum inhibitory concentration (MIC) whatever the number of topoisomerase mutations, and qnrS was additive to qnrA with a further 2- to 10-fold increase in the MIC. Comparison of MICs with susceptibility breakpoints showed that strains combining qnrA and topoisomerase mutations were resistant to fluoroquinolones, but the three strains lacking a topoisomerase mutation were susceptible using ciprofloxacin and levofloxacin but not using nalidixic acid or moxifloxacin testing.     

Phenotypic and genotypic analysis of levofloxacin-resistant clinical isolates of Streptococcus pneumoniae collected in 13 countries during 1999-2000

During 1999-2000, 5015 isolates were collected from 13 countries and tested against levofloxacin. Overall, levofloxacin resistance minimum inhibitory concentration (MIC>or =8 mg/l) was found in 40 isolates (0.8%). The highest resistance rates were in Hong Kong (8.0%), China (3.3%) and Spain (1.6%). Levofloxacin retained an MIC(90) of 1 mg/l in all countries. Pulsed-field gel electrophoresis analysis of resistant isolates demonstrated the presence of clones in countries where levofloxacin resistance exceeded 1%, suggesting that the elevated resistance rates could result from resistant clones within participating hospitals. DNA-sequence analysis of the quinolone-resistance-determining regions of gyrA, gyrB, parC and parE genes showed that the most common mutations were in GyrA (Ser81Phe), ParC (Ser79Phe, Lys137Asn) and ParE (Ile460Val), accounting for 40% of the isolates tested. Levofloxacin-resistant isolates were generally non-susceptible to other fluoroquinolones tested. Future studies to characterise resistant isolates by other molecular methods may ensure that the appropriate counter-measures can be taken to control the spread of resistant isolates.     

In vitro activity of older and newer fluoroquinolones against efflux-mediated high-level ciprofloxacin-resistant Streptococcus pneumoniae

The effect of high-level efflux activity on the MICs of fluoroquinolones against Streptococcus pneumoniae in the absence of topoisomerase mutations leading to fluoroquinolones resistance was investigated. A S. pneumoniae ATCC 46619-derived strain with high-level efflux activity was obtained (SP-25A). Both the parent and obtained strains were tested against efflux substrates acriflavine (Acr) and ethidium bromide (EtBr), and against norfloxacin (NFX), ciprofloxacin (CFX), levofloxacin (LFX), moxifloxacin (MFX), trovafloxacin (TVX) and sitafloxacin (SFX), in presence and absence of the efflux pump inhibitor reserpine. gyrA, gyrB, parC and parE QRDR genes were amplified by PCR and sequenced. MICs of NFX and CFX against SP-25A were 64-fold higher than parent strain MICs (256 mg/L versus 4 mg/L and 64 mg/L versus 1mg/L, respectively). MIC of LFX increased from 1 to 4 mg/L and MICs of MFX, TVX and SFX remained virtually unchanged (0.1-0.2 mg/L). MICs of Acr and EtBr against SP-25A were 8- and 16-fold higher than against parent strains. In both cases, reserpine reverted MICs to the parent strain values (1 and 0.2 mg/L). Only parE showed two mutations leading to a Pro(454) --> Ser and Glu(443) changes, which have previously been shown not to lead to significant fluoroquinolones MIC increases. SP-25A showed a significant increase of MICs of the hydrophilic fluoroquinolones, apparently derived only from efflux activity. Efflux activity, at these high levels, can lead to high-level resistance to older hydrophilic fluoroquinolones, but does affect newer fluoroquinolones such as moxifloxacin, trovafloxacin and sitafloxacin.     

Contribution of mutations in DNA gyrase and topoisomerase IV genes to ciprofloxacin resistance in Escherichia coli clinical isolates

DNA gyrase (GyrA and GyrB) and topoisomerase IV (ParC and ParE) are the two essential type II topoisomerases in Escherichia coli. These enzymes act via inhibition of DNA replication. Mutations in the quinolone resistance-determining region (QRDR) of the gyrA, gyrB, parC and parE genes from clinical isolates of E. coli were determined by DNA sequencing of 54 ciprofloxacin-resistant clinical isolates from a hospital in Delhi, India. The majority of the E. coli isolates were shown to carry mutations in gyrA, parC and parE. Ciprofloxacin resistance due to accumulation of such a high number of mutations in the QRDR regions of gyrA at positions Ser83 and Asp87 and parC at position Ser80 as well as outside of the QRDR region of parE at Ser458 and Glu460 confers high-level resistance of ciprofloxacin in clinical isolates. The high frequency of occurrence of mutations in the parE gene (44.4% strains) is alarming, as topoisomerase IV is a secondary target of quinolones.     

In vitro activity of moxifloxacin against recent community-acquired respiratory tract pathogens isolated in France: a national survey

Between February and June 2000, 2345 consecutive strains of Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis, Staphylococcus aureus and Klebsiella pneumoniae were isolated from 2088 adult patients suffering from community-acquired respiratory tract infections, in 97 hospital laboratories. Of the 1037 S. pneumoniae isolates, 48.3% were intermediately or highly penicillin resistant. For invasive isolates, the MIC90s of penicillin G, amoxycillin, cefuroxime, ceftriaxone, erythromycin, ofloxacin, ciprofloxacin and moxifloxacin were 2, 2, 4, 0.5, 1024, 2, 2 and 0.25 mg/l, respectively. All but one invasive strain were susceptible to moxifloxacin whereas 97.5% were susceptible to levofloxacin. The MIC90s of clinical isolates with intermediate susceptibility or high resistance to penicillin G, were 2, 2, 4, 1, 1024, 2, 2 and 0.25 mg/l. About 98.1, 97.0, and 83.1% of strains were inhibited by concentrations < or = 1 mg/l of moxifloxacin, levofloxacin and ciprofloxacin, respectively (E-test). Eight of the 1037 S. pneumoniae strains were not susceptible to moxifloxacin and had mutations in gyrA (eight strains), parC (four strains) or parE (three strains). Against H. influenzae (32.7% were beta-lactamase producers) and M. catarrhalis (96.3% were beta-lactamase producers), the MIC90s of moxifloxacin, amoxycillin and co-amoxiclav were 0.094 and 0.125 mg/l, 64 and 8 mg/l, and 1.5 and 0.25 mg/l, respectively. Against oxacillin-susceptible S. aureus and K. pneumoniae, the MIC90s of moxifloxacin were 0.125 and 0.84 mg/l respectively. Moxifloxacin had the highest in vitro activity of all antibiotics tested.     

Increased antibacterial activity of DW286, a novel fluoronaphthyridone antibiotic, against Staphylococcus aureus strains with defined mutations in DNA gyrase and topoisomerase IV

To investigate the activity of DW286, a new fluoronaphthyridone, the quinolone resistance determining regions (QRDRs) of gyrA, gyrB, grlA and grlB genes in 64 Staphylococcus aureus clinical isolates were analyzed and the MICs of DW286 and comparator quinolones determined. Double and triple mutants in gyrA and grlA were resistant to ciprofloxacin, sparfloxacin, trovafloxacin and gemifloxacin but susceptible to DW286 (MIC 0.25-0.5 mg/l). The fourth alteration, Ser85Pro of GyrA was required to make a strain resistant to DW286 (MIC 4-32 mg/l). For a strain with the mutations at GyrA Ser84Leu and GrlA Ser80Phe, the MBC of DW286 was two-fold higher than its corresponding MIC, in contrast to ciprofloxacin which was not bactericidal.     

In vitro activity of sitafloxacin against clinical isolates in 2009

In vitro activity of sitafloxacin (STFX) and various oral antimicrobial agents against bacterial isolates recovered from clinical specimens between January and December 2009, at different healthcare facilities in Japan was evaluated. A total of 1,620 isolates including aerobic and anaerobic organisms was available for the susceptibility testing using the microbroth dilution methods recommended by Clinical Laboratory Standard Institute. The minimum inhibitory concentration of STFX at which 90% of isolates (MIC90) was 0.06 microg/mL for methicillin-susceptible Staphylococcus aureus and was equal to that of garenoxacin (GRNX), 2 times lower than that of moxifloxacin (MFLX), and 8 times lower than that of levofloxacin (LVFX). STFX inhibited the growth of all the isolates of Streptococcus pneumoniae at 0.06 microg/mL or less. The MIC90s of STFX ranged from 0.03 to 0.06 microg/mL and were 1 to 2 times lower than those of GRNX, 2 to 4 times lower than those of MFLX, and 16 to 32 times lower than those of LVFX. Against Streptococcus pyogenes, the MIC90 of STFX was 0.06 microg/mL and was 2 times lower than that of GRNX, 4 times lower than that of MFLX, and 32 times lower than that of LVFX. The MIC90 of STFX was 0.25 microg/mL for Enterococcus faecalis, and was 2 times lower than those of GRNX and MFLX, and 8 times lower than that of LVFX. The MIC90 of STFX for E. coli was 2 microg/mL, and the MIC90s of other 10 species of Enterobacteriaceae which were the lowest values of the quinolones tested ranged from 0.03 to 1 microg/mL. The MIC90 of STFX for Pseudomonas aeruginosa isolates recovered from urinary infections was 8 microg/mL and was 16 times lower than those of GRNX, MFLX and LVFX. The MIC90 of STFX for P aeruginosa isolates recovered from respiratory infections was 2 microg/mL and was 32 times lower than those of GRNX and MFLX, and 16 times lower than that of LVFX. STFX inhibited the growth of all the isolates of Haemophilus influenzae at 0.004 microg/mL or less, and was 2 to 4 times lower than those of GRNX, 8 times lower than those of MFLX, and 4 times lower than those of LVFX. The MIC90 of STFX was 0.008 microg/mL for Moraxella catarrhalis, and was 2 times lower than that of GRNX, 8 times lower than those of MFLX and LVFX. The MIC90s of STFX ranged from 0.015 to 0.12 microg/mL for all the species of anaerobic bacteria and were the lowest values of all the antimicrobial agents tested. In conclusion, the activity of STFX against Gram-positive cocci was comparable or superior to those of GRNX, MFLX and LVFX. STFX showed the most potent activity against Gram-negative bacteria and anaerobic bacteria of all the antimicrobial agents tested in this study.     

Susceptibility of major pathogens of acute pharyngitis and tonsillitis to levofloxacin and other oral antimicrobial drugs

A total of 2865 strains of the causative organisms isolated from the patients with acute pharyngitis and tonsillitis at the primary medical institutions were used in this study. The MICs of levofloxacin (LVFX) and other oral antimicrobial drugs were determined and evaluated by the NCCLS guideline. LVFX, cefditoren (CDTR) and cefcapene (CFPN) were potently active against 773 isolates of Hemophilus influenzae, the MIC50S of LVFX being < or = 0.06 microgram/mL and also the same as the MIC90S of LVFX. LVFX was the most active against 496 isolates of Enterobacteriaceae. The MIC50S of LVFX were < or = 0.06 microgram/mL and were lower than those of CDTR, cefdinir (CFDN) and cefpodoxime (CPDX) (MIC50S: 0.5 microgram/mL). The MIC90S of these cephems were markedly higher than the respective MIC50S, whereas MIC50 of LVFX was 0.12 microgram/mL, only twice the MIC50. Against the majority of Streptococcus pyogenes (555 isolates) and Streptococcus spp. (495 isolates), CDTR, CFDN, CPDX and CFPN were highly active (MICs: < or = 0.06 microgram/mL), and clarithromycin (CAM) and azithromycin (AZM) were also active against these organisms (MICs: 0.12 to 0.25 microgram/mL). Against S. pneumoniae (92 isolates), CDTR and CFDN were active (MIC50S: 0.12 and 0.25 microgram/mL, respectively). However, the MIC90S of these drugs were 4-8 times the MIC50S. Against Moraxella (Branhamella) catarrhalis (454 isolates), LVFX was potently active, the MIC90 of LVFX being < or = 0.06 microgram/mL and MIC90S of the other cephems being 0.5 microgram/mL or more. When the susceptibility of these strains to LVFX was evaluated by the NCCLS guideline, about 3% of other Streptococcus spp. were resistant to the drug but no test strains resistant to LVFX were detected in H. influenzae, S. pyogenes or Enterobacteriaceae. On the other hand, the percentages of strains susceptible to the cephems tested were 60-90%, which were quite different according to kinds of drugs and species used. Furthermore, the strains of S. pneumoniae resistant to CFDN and CPDX, and those to CAM and AZM were 21-25% and 50% or more, respectively, whereas no LVFX-resistant strains were detected. The major pathogens isolated from patients with pharyngitis and tonsillitis in the primary institutions were highly susceptible to LVFX. These results suggest that LVFX is a useful drug which is potently active against the strains resistant to oral cephem and macrolide antibiotics.     

Correlation between in vitro and in vivo activity of levofloxacin and moxifloxacin against pneumococcal strains with different susceptibilities to fluoroquinolones

In vitro and in vivo models were developed to evaluate the efficacy of levofloxacin and moxifloxacin against three serotype 3 pneumococcal strains with different susceptibilities to fluoroquinolones (wild-type, parC mutant, and parC, parE and gyrA mutant). Levofloxacin and moxifloxacin reduced the bacterial burden in the in vitro pharmacodynamic and animal models for the wild-type strain but had very little activity against the fully resistant strain (parC, parE and gyrA mutant). Levofloxacin showed very little activity both in the in vitro pharmacodynamic model and in the animal model for the strain having a mutation in parC (levofloxacin and moxifloxacin minimum inhibitory concentrations, 2mg/L and 0.25mg/L, respectively). However, moxifloxacin still had a significant in vitro and in vivo activity against this strain.     

Selection of a gyrA mutation and treatment failure with gatifloxacin in a patient with Streptococcus pneumoniae with a preexisting parC mutation

An 81-year-old woman had pneumonia caused by Streptococcus pneumoniae (levofloxacin Etest minimum inhibitory concentration [MIC] 1.5 microg/ml) and was treated with intravenous gatifloxacin 200 mg/day. After 3 days of therapy, repeat sputum cultures were positive for S. pneumoniae, which was resistant to levofloxacin (Etest MIC > 32 microg/ml). The isolate obtained before therapy showed a preexisting parC mutation of aspartic acid-83 to asparagine (Asp83-->Asn), and the isolate obtained during therapy showed an acquired gyrA mutation from serine-81 to phenylalanine (Ser81-->Phe) and a second parC mutation from lysine-137 to Asn (Lys137-->Asn). Both isolates were the same strain, as determined with pulsed-field gel electrophoresis. This case demonstrates the potential for resistance to emerge during 8-methoxy fluoroquinolone therapy for fluoroquinolone-susceptible S. pneumoniae with a preexisting parC mutation. Additional clinical failures with a fluoroquinolone may occur unless these first-step parC mutants can be identified to assist clinicians in selecting appropriate antimicrobial therapy.     

耐氟喹诺酮类铜绿假单胞菌gyrA及parC基因突变研究

目的　研究临床分离的耐氟喹诺酮类铜绿假单胞菌gyrA及parC基因突变情况。方法　测定临床分离的 5 5株铜绿假单胞菌MIC值 ,从中筛选出 1株敏感菌和 8株耐药菌 ,以标准敏感菌株ATCC2 785 3作为质控菌株。用聚合酶链反应 (PCR)扩增gyrA及parC基因的喹诺酮耐药决定区 (QR DR) ,扩增产物片段长度分别为 35 1bp、397bp。用限制性内切酶SacⅡ消化gyrAPCR产物 ,同时对上述 10株菌的gyrA及parC基因的喹诺酮决定区 (QRDR)进行PCR DNA直接测序分析。结果　有 8株耐菌株的gyrA基因在 83位 (ACC→ATC)有突变 ,导致氨基酸Thr→Ile的改变 ;有 3株高度耐药菌gyrA基因同时在 87位 (GAC→GGC)有突变 ,导致氨基酸Asp→Gly的改变 ;有 4株耐药菌株的parC基因在 87位有TCG→TTG突变 ,导致氨基酸由Ser→Leu的改变。同时具gy rA和parC突变MIC值是仅具gyrA突变菌株MIC值的 2～ 16倍。未发现parC突变单独存在。另外 ,有 6株耐药菌gyrA的 132位有CAC→CAT的突变 ;所有耐药菌株parC基因 115位有GCT→GCG的突变 ,该突变未引起氨基酸的改变。结论　gyrA83、87位突变及parC基因 87位突变都可引起铜绿假单胞菌对氟喹诺酮类药物产生耐药 ,但以gyrA基因 83位突变为主 ,合并gyrA基因 87位及parC基因 87位突变可增加耐药程度。     

In vivo activity of gemifloxacin, moxifloxacin and levofloxacin against pneumococci with gyrA and parC point mutations in a sepsis mouse model measured with the all or nothing mortality end-point

A dose-decreasing immunocompetent sepsis mouse model was used to evaluate the in vivo effect of levofloxacin, moxifloxacin and gemifloxacin, using a ciprofloxacin/levofloxacin susceptible serotype 6B strain (ciprofloxacin MIC: 1 mg/l) and two resistant serotype 14 and 19F strains with gyrA and parC point mutations (ciprofloxacin MICs of 32 and 64 mg/l, respectively). Significant higher in vivo activity was found for moxifloxacin and gemifloxacin than for levofloxacin against strains 1 and 2, and for gemifloxacin versus moxifloxacin or levofloxacin against strain 3. Gemifloxacin treatment resulted in 100% survival against strains 1 and 2(AUC0-24 h/MIC of 30 and 62) but against strain 3, survival was 60-80% (AUC0-24 h/MIC of 93). Similar AUC0-24 h/MIC values produced different therapeutic results suggesting that in vitro parameters other than the MIC could influence efficacy predictions based on in vitro susceptibility tests (MICs) or pharmacodynamic parameters (AUC0-24 h/MIC).     

In vitro activity of gemifloxacin against clinical isolates of Neisseria gonorrhoeae with and without mutations in the gyrA gene

The MIC of gemifloxacin and five other quinolones was tested against 31 clinical isolates of Neisseria gonorrhoeae; strains were analyzed for the presence of mutations in both the gyrA and parC genes. Only seven strains were resistant to nalidixic acid due to a mutation in the gyrA gene but not in the parC gene, with six and two considered intermediate to ciprofloxacin and levofloxacin, respectively. The activity of gemifloxacin was similar to that of trovafloxacin and moxifloxacin, but was more active than nalidixic acid, ciprofloxacin or levofloxacin against the gyrA mutant strains. Gemifloxacin is a valid therapeutic alternative to treat infections with N. gonorrhoeae, retaining its activity against strains already presenting a mutation in gyrA.     

Evaluation of survival and pharmacodynamic relationships for five fluoroquinolones in a neutropenic murine model of pneumococcal lung infection

STUDY OBJECTIVE: To compare the antistreptococcal activity of five fluoroquinolone antibiotics, using a neutropenic murine model of pneumococcal pulmonary infection. DESIGN: Animal experiment. SETTING: University-affiliated research center. ANIMALS: Neutropenic and control mice weighing 24-29 g. INTERVENTION: After induction of neutropenia, renal failure, and infection with Streptococcus pneumoniae, the mice received one of five fluoroquinolones twice/day for 72 hours beginning 12 hours after infection. Dosages were selected to approximate 0.1 x AUC0-24 (area under the concentration-time curve from 0-24 hours) and AUC0-24 achieved in humans. Control mice received normal saline. Survival was assessed at regular intervals for up to 10 days. At least 10 mice were included in each cohort (range 10-34). MEASUREMENTS AND MAIN RESULTS: Ciprofloxacin, clinafloxacin, grepafloxacin, levofloxacin, and moxifloxacin were studied at subtherapeutic and therapeutic dosages against three quinolone-susceptible isolates of S. pneumoniae that lacked mutations in parC, parE, and gyrA. Pharmacokinetic profile of each agent and dosing regimen was determined. A composite survival curve for all fluoroquinolones and isolates was constructed. Relationships between survival rate at 72 hours and AUC:MIC (minimum inhibitory concentration), peak:MIC, time above the MIC (percentage of dosing interval) for total and free drug concentrations were fit by using a sigmoid maximal effect (Emax) model. Survival was significantly better in the higher dosage group than in the lower dosage group. Time above MIC did not display a correlation with outcome. The AUC:MIC showed a greater correlation with outcome (R2 = 0.56 total, 0.54 free) than did peak:MIC (R2 = 0.52 total, 0.51 free). With use of composite data, total AUC:MIC ratios associated with 50%, 90%, and 99% of Emax were 34:1, 56:1, and 95:1, respectively CONCLUSIONS: In this model, efficacy was achieved with the fluoroquinolone antibiotics at dosages yielding AUC0-24 comparable to those obtained in humans. One pharmacodynamic parameter (i.e., AUC:MIC) may be applied to various fluoroquinolones and isolates of S. pneumoniae. The AUC:MIC was more predictive of outcome than was time above the MIC or peak:MIC.     

Clinically significant borderline resistance of sequential clinical isolates of Klebsiella pneumoniae

Two sequential clinical isolates of Klebsiella pneumoniae (Kpn) were isolated from bronchoalveolar lavage fluid (Kpn#1) and sputum (Kpn#2) of a patient with pneumonia, complicated by anatomical and immunosuppressive problems due to Wegener's granulomatosis. Despite 4 weeks of systemic treatment with ciprofloxacin (CIP) Kpn#2 was isolated thereafter. A fluoroquinolone-resistant mutant (Kpn#1-SEL) was derived from Kpn#1 in vitro by selecting on agar plates supplemented with ofloxacin. Kpn#1, Kpn#1-SEL and Kpn#2 had an identical pattern in PFGE. CIP MICs were 0.25, 2 and 4 mg/l for Kpn#1, Kpn#2 and Kpn#1-SEL, respectively. Kpn ATCC 10031 (CIP MIC 0.002 mg/l) served as control. We analyzed mechanisms of fluoroquinolone resistance by determining antibiotic susceptibility, organic solvent tolerance, accumulation of fluoroquinolones, dominance testing with wild-type topoisomerase genes (gyrA/B, parC/E), sequencing of the quinolone resistance determining regions of gyrA/B, parC/E and marR and Northern blotting of marR and acrAB genes. Compared with Kpn ATCC 10031, elevated MICs to fluoroquinolones and unrelated antibiotics in Kpn#1 was presumably due to a primary efflux pump other than AcrAB and increased the CIP MIC 125-fold. Although Kpn#1 tested sensitive according to NCCLS breakpoints, the elevated CIP MIC of 0.25 mg/l presumably rendered this isolate clinically resistant and lead to therapeutic failure in this case. Further increase of MIC to fluoroquinolones in vivo and in vitro was distinct. Kpn#1-SEL, selected in vitro, acquired a GyrA target mutation, whereas in Kpn#2 no known resistance mechanism could be detected.     

大肠埃希菌gyrA、parC和marOR基因突变与喹诺酮耐药的相关性

目的:研究大肠埃希菌gyrA、parC和marOR基因突变与喹诺酮类耐药的相关性。方法:采用微量稀释法进行常规药敏试验,筛选3株萘啶酸敏感大肠埃希菌和37株萘啶酸耐药大肠埃希菌株;PCR扩增大肠埃希菌喹诺酮耐药决定区(QRDR)相关gyrA、parC基因,进行聚合酶链反应-单链构象多态性(PCR-SSCP)分析,同时PCR扩增marOR基因;在耐药株选取部分菌株对gyrA、parC及marOR基因进行测序,检测其突变情况,其结果与体外药敏试验结果进行比较,研究其相关性。结果:37株耐药株均出现gyrA基因突变,但对环丙沙星低耐株最低抑菌浓度(MIC)=2mg/L只出现gyrA单位点突变,而parC基因未发生突变;环丙沙星高耐株(MIC=64mg/L)gyrA基因出现3个位点突变,parC基因出现单位点突变;在环丙沙星高耐株(MIC=256mg/L),并伴有其他类抗菌药物的多重耐药时,除了出现gyrA和parC基因双位点突变,同时检测到marOR基因的多位点突变。结论:gyrA和parC基因突变在大肠埃希菌对喹诺酮耐药中起着重要作用,gyrA和parC基因突变的程度与大肠埃希菌耐药水平有关,marOR基因多位点突变在多重耐药机制中具有一定的作用。     

泵抑制剂对耐喹诺酮类铜绿假单胞菌临床株作用的研究

目的　了解四种泵抑制剂对喹诺酮类耐药铜绿假单胞菌株耐药水平的降低作用与耐药决定区基因突变及耐药表型的关系。方法　采用羰基氰氯苯腙 (CCCP)、利舍平、维拉帕米及奥美拉唑以琼脂稀释法分别加入喹诺酮耐药的菌株中 ,与喹诺酮类抗生素共同作用 ,并同时测定其最低抑菌浓度 (MIC)的变化。对部分耐药株 Gyr A和 Par C区进行 PCR- RFL P分析 ,并行 DNA测序观察突变情况。结果　四种泵抑制剂中CCCP能极大的降低 MIC的值。利舍平也可部分减低 MIC的值 ,但维拉帕米及奥美拉唑作用轻微。高度耐药株存在 gyr A和 par C的突变。结论　寻找理想的泵抑制剂可降低铜绿假单胞菌的耐药水平。     

PROTEKT 1999-2000: a multicentre study of the antibiotic susceptibility of respiratory tract pathogens in Hong Kong, Japan and South Korea

A multicentre surveillance study performed in the Far East during 1999-2000 investigated the in vitro activity of >20 antibacterials against common respiratory pathogens. In Hong Kong, Japan, and South Korea, 57.1, 44.5 and 71.5% Streptococcus pneumoniae were penicillin-resistant and 71.4, 77.9 and 87.6% were erythromycin-resistant, respectively. Overall, >90% of penicillin-resistant strains were also macrolide-resistant. All strains were susceptible to telithromycin. Fluoroquinolone-resistant isolates in Japan (1.3%), Hong Kong (14.3%) and South Korea (2.9%) were mostly co-resistant to penicillin, macrolides and tetracycline. Beta-lactamase production by Haemophilus influenzae isolates was 8.5% in Japan, 17.1% in Hong Kong and 64.7% in strains from South Korea. A single (0.27%) BLNAR isolate was obtained in Japan. There was no fluoroquinolone resistance. Moraxella catarrhalis was inhibited by telithromycin at 相似文献   

In vitro activities of levofloxacin and other antibiotics against fresh clinical isolates

In this study, the in vitro activity of levofloxacin (LVFX) against 1,020 fresh bacterial clinical isolates was compared with the activities of a range of ofloxacin, ciprofloxacin (CPFX), ampicillin (ABPC), cefaclor, cefpodoxime, methicillin and benzylpenicillin. The clinical isolates except Vibrio cholerae were collected in Japan during 1998 from patients with infectious diseases. MICs were determined using the agar dilution method according to the recommendations by the Japan Society of Chemotherapy. Some isolates of methicillin resistant Staphylococcus aureus (MRSA) and coagulase negative Staphylococcus were resistant to fluoroquinolones, but the MIC50 of LVFX against MRSA was 6.25 micrograms/ml. LVFX was the most active against MRSA among the antibiotics tested. Most of Staphylococcus epidermidis strains were susceptible to the fluoroquinolones. LVFX showed greater activity against all streptococci strains compared with fluoroquinolones tested. In particular, all Streptococcus pneumoniae strains including PRSP were susceptible to LVFX at < or = 1.56 micrograms/ml. Among Enterococcus, ABPC showed superior activity against Enterococcus faecalis but many isolates of Enterococcus species were resistant to ABPC. LVFX was more active against to these Enterococcus species compared with other fluoroquinolones. On the other hand, LVFX and CPFX showed similar activity against isolates of Enterobacteriaceae. CPFX had an MIC50/90 of 0.20, 0.39 microgram/ml and LVFX showed an MIC50/90 of 0.78, 1.56 micrograms/ml against Pseudomonas aeruginosa. LVFX (MIC50/90 0.10, 0.20 microgram/ml) was more active against Acinetobacter species than CPFX (MIC50/90 0.10, 0.39 microgram/ml). Haemophilus influenzae, Branhamella (Moraxella) catarrhalis and V. cholerae were inhibited by low concentration of the fluoroquinolones tested. The MIC90 of LVFX and CPFX were < or = 0.10 microgram/ml against above three species. Some isolates of Neisseria gonorrhoeae and Campylobacter species were moderately resistant to the fluoroquinolones tested but the MIC50 of LVFX and CPFX were < or = 0.39 microgram/ml. Among anaerobes, Propionibacterium acnes was more susceptible than Peptostreptococcus species, and the MIC90 of beta-lactams and fluoroquinolones tested were < or = 0.78 microgram/ml. In conclusion, this study, performed on large number of strains, confirmed an excellent and wide spectrum antibacterial activity of LVFX compared with the fluoroquinolones and beta-lactams tested. And our results suggest that LVFX may be useful in the treatment of various bacterial infections.     

Analysis of mutations within multiple genes associated with resistance in a clinical isolate of Neisseria gonorrhoeae with reduced ceftriaxone susceptibility that shows a multidrug-resistant phenotype

A Neisseria gonorrhoeae strain with a reduced susceptibility to ceftriaxone (minimum inhibitory concentration (MIC) = 0.5 microg/mL) was isolated among 398 clinical isolates obtained from 2000-2001 in Fukuoka City, Japan. The N. gonorrhoeae strain was negative for penicillinase production but it showed multidrug resistance against penicillin (MIC = 8 microg/mL), tetracycline (MIC = 4 microg/mL), azithromycin (MIC = 0.5 microg/mL) and ciprofloxacin (MIC = 16 microg/mL). The molecular mechanisms of the multidrug-resistant phenotype in this strain were analysed. Polymerase chain reaction and direct DNA sequencing were performed to identify mutations within the penA, ponA, mtrR, penB, gyrA and parC genes of the gonococcal strain, which thus explain the multidrug-resistant phenotype. The N. gonorrhoeae strain contained a significantly different sequence of the penA gene from that of the ceftriaxone-susceptible strains. Some regions of the transpeptidase domain within this penA gene were closely similar to those found in other Neisseria species such as Neisseria subflava, Neisseria flavescens or Neisseria perflava/sicca. This strain also included a ponA mutation that is associated with high-level resistance to penicillin, mtrR mutations that mediate overexpression of the MtrCDE efflux pump responsible for resistance to hydrophobic agents such as azithromycin, and penB mutations that reduce porin permeability to hydrophilic agents such as tetracycline. Moreover, this strain contained gyrA and parC mutations that confer high-level resistance to ciprofloxacin. These results indicate the emergence of a N. gonorrhoeae strain with reduced susceptibility to ceftriaxone, which also showed a multidrug-resistant phenotype that can be explained by the presence of multiple loci mutations associated with antibiotic resistance.