Fluoroquinolone resistance in clinical isolates of Streptococcus pneumoniae: contributions of type II topoisomerase mutations and efflux to levels of resistance

Ubiquitous Nature of Fluoroquinolones: The Oscillation between Antibacterial and Anticancer Activities

Fluoroquinolones are synthetic antibacterial agents that stabilize the ternary complex of prokaryotic topoisomerase II enzymes (gyrase and Topo IV), leading to extensive DNA fragmentation and bacteria death. Despite the similar structural folds within the critical regions of prokaryotic and eukaryotic topoisomerases, clinically relevant fluoroquinolones display a remarkable selectivity for prokaryotic topoisomerase II, with excellent safety records in humans. Typical agents that target human topoisomerases (such as etoposide, doxorubicin and mitoxantrone) are associated with significant toxicities and secondary malignancies, whereas clinically relevant fluoroquinolones are not known to exhibit such propensities. Although many fluoroquinolones have been shown to display topoisomerase-independent antiproliferative effects against various human cancer cells, those that are significantly active against eukaryotic topoisomerase show the same DNA damaging properties as other topoisomerase poisons. Empirical models also show that fluoroquinolones mediate some unique immunomodulatory activities of suppressing pro-inflammatory cytokines and super-inducing interleukin-2. This article reviews the extended roles of fluoroquinolones and their prospects as lead for the unmet needs of "small and safe" multimodal-targeting drug scaffolds.

Fluoroquinolone resistance in Streptococcus pneumoniae isolates in Germany from 2004-2005 to 2014-2015

Streptococcus pneumoniae is a major cause of bacterial pneumonia, sepsis and meningitis worldwide. Prevalence of levofloxacin-resistant S. pneumoniae isolates in Germany and associated mutations in the quinolone resistance determining regions (QRDRs), as well as serotype distribution and multi locus sequence types (MLST) are shown. 21,764 invasive S. pneumoniae isolates from Germany, isolated in the epidemiological seasons from 2004/05 to 2014/15 were analyzed at the German National Reference Centre for Streptococci (GNRCS) for their levofloxacin resistance by micro broth dilution method. All resistant (minimal inhibitory concentration (MIC) ≥8μg/ml) and intermediate (MIC >2μg/ml and <8μg/ml) isolates were selected for the present study. Additionally, 29 susceptible isolates were randomly selected. A total of ninety isolates were tested for their levofloxacin-MIC by Etest, their serotype and sequence type, as well as for point-mutations at the QRDRs in the genes parC, parE, gyrA and gyrB. Twenty-five isolates exhibited levofloxacin MICs <2μg/ml (Etest) and no mutations in the QRDRs. Four isolates with MICs=2μg/ml had one mutation in parC; isolates with MICs >2μg/ml all had one or more mutations in the QRDRs. Four of nine intermediate isolates had a mutation in either parC or gyrA, and four isolates had mutations in both parC and gyrB. One isolate had mutations in both parC and gyrA. All isolates with MICs ≥8μg/ml (52) had mutations in both topoisomerase IV and gyrase. Serotypes associated with levofloxacin resistance shifted from a majority of PCV13 serotypes before the introduction of the PCV13 vaccine towards non-PCV serotypes. Resistant isolates were almost exclusively found among adults (98.1%).

Deoxynybomycins inhibit mutant DNA gyrase and rescue mice infected with fluoroquinolone-resistant bacteria

Fluoroquinolones are one of the most commonly prescribed classes of antibiotics, but fluoroquinolone resistance (FQR) is widespread and increasing. Deoxynybomycin (DNM) is a natural-product antibiotic with an unusual mechanism of action, inhibiting the mutant DNA gyrase that confers FQR. Unfortunately, isolation of DNM is difficult and DNM is insoluble in aqueous solutions, making it a poor candidate for development. Here we describe a facile chemical route to produce DNM and its derivatives. These compounds possess excellent activity against FQR methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococci clinical isolates and inhibit mutant DNA gyrase in-vitro. Bacteria that develop resistance to DNM are re-sensitized to fluoroquinolones, suggesting that resistance that emerges to DNM would be treatable. Using a DNM derivative, the first in-vivo efficacy of the nybomycin class is demonstrated in a mouse infection model. Overall, the data presented suggest the promise of DNM derivatives for the treatment of FQR infections.

Fluoroquinolone antibiotics are widely used to treat serious bacterial infections, but resistance is an increasing problem. Here the authors describe the synthesis and characterization of novel deoxynybomycin derivatives that exhibit activity against fluoroquinolone-resistant infections in an in vivo model.

Bacillus anthracis GrlAV96A topoisomerase IV, a quinolone resistance mutation that does not affect the water-metal ion bridge

The rise in quinolone resistance is threatening the clinical use of this important class of broad-spectrum antibacterials. Quinolones kill bacteria by increasing the level of DNA strand breaks generated by the type II topoisomerases gyrase and topoisomerase IV. Most commonly, resistance is caused by mutations in the serine and acidic amino acid residues that anchor a water-metal ion bridge that facilitates quinolone-enzyme interactions. Although other mutations in gyrase and topoisomerase IV have been reported in quinolone-resistant strains, little is known regarding their contributions to cellular quinolone resistance. To address this issue, we characterized the effects of the V96A mutation in the A subunit of Bacillus anthracis topoisomerase IV on quinolone activity. The results indicate that this mutation causes an ∼ 3-fold decrease in quinolone potency and reduces the stability of covalent topoisomerase IV-cleaved DNA complexes. However, based on metal ion usage, the V96A mutation does not disrupt the function of the water-metal ion bridge. A similar level of resistance to quinazolinediones (which do not use the bridge) was seen. V96A is the first topoisomerase IV mutation distal to the water-metal ion bridge demonstrated to decrease quinolone activity. It also represents the first A subunit mutation reported to cause resistance to quinazolinediones. This cross-resistance suggests that the V96A change has a global effect on the structure of the drug-binding pocket of topoisomerase IV.

High prevalence of Streptococcus agalactiae from vaginas of women in Taiwan and its mechanisms of macrolide and quinolone resistance

BACKGROUND/PURPOSE

Streptococcus agalactiae (GBS), is the most common pathogen causing infections among perinatal women and neonatal babies. Nonetheless, there are few studies on the occurrence of GBS among the pregnant women and the mechanisms of GBS resistance to quinolones and macrolides in Taiwan.

METHODS

GBS were isolated from vaginas of the pregnant and non-pregnant symptomatic women in Taiwan. The prevalence, antimicrobial susceptibility, and mechanisms of resistance against erythromycin and quinolone of total 188 isolates were studied.

RESULTS

The isolation rate of GBS from pregnant women was significantly higher at 21.8% compare with the non-pregnant women of 13.2%. Antibiotic susceptibility test of the 188 GBS isolates revealed a high non-susceptible rate for erythromycin (50.0%) while the rate for levofloxacin was only 4.8%. Among 94 erythromycin non-susceptible GBS isolates, ermB gene was detected 83.1% (59/71) for those GBS that were non-susceptible to both clindamycin and tetracycline, which was significantly higher than GBS that are susceptible to clindamycin but resistant to tetracycline at 43.8% (7/16). No ermA or mef gene was detected in any isolate. Mutations were detected in the parC and gyrA genes in 14 out of 18 levofloxacin non-susceptible isolates. The predominant mutation type was the combination of Ser79Tyr in parC and Ser81Leu mutations in gyrA.

CONCLUSION

GBS is the most common isolated pathogens in vaginal infections in Taiwan, resistance to tetracycline and erythromycin is higher than the rate observed for other regions of the world, while the resistance rate for levofloxacin was relatively lower in Taiwan.

Antiproliferative and cytotoxic properties of moxifloxacin on rat retinal ganglion cells

Abstract Purpose: To evaluate the antiproliferative and cytotoxic properties of moxifloxacin on cultured rat retinal ganglion cells (RGC5).

MATERIALS AND METHODS

Rat retinal ganglion cells were exposed to various concentration of moxifloxacin (5-1500 μg/mL). For antiproliferative properties, the 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) test was performed. Cellular cytotoxicity was assessed by using the Live/Dead viability/cytotoxicity assay and analyzed by fluorescence microscopy after 24 and 72 h of incubation, respectively.

RESULTS

Neither cytotoxic nor antiproliferative effect of moxifloxacin was observed below 50 μg/mL on RGC5 cells after 24 and 72 h of incubation. At higher concentrations of moxifloxacin (150 μg/mL, 500 μg/mL, and 1500 μg/mL (p < 0.001)) the number of viable cells and the proliferation rate of RGC5 were significantly reduced.

CONCLUSIONS

These results suggest a dose-dependent cytotoxic and antiproliferative effect of moxifloxacin on RGC5. Therefore, intracameral application of moxifloxacin should be used cautiously in patients with increased risk of retinal ganglion cells damage, particularly in glaucoma patients.

Genomic characterization of ciprofloxacin resistance in a laboratory-derived mutant and a clinical isolate of Streptococcus pneumoniae

The broad-spectrum fluoroquinolone ciprofloxacin is a bactericidal antibiotic targeting DNA topoisomerase IV and DNA gyrase encoded by the parC and gyrA genes. Resistance to ciprofloxacin in Streptococcus pneumoniae mainly occurs through the acquisition of mutations in the quinolone resistance-determining region (QRDR) of the ParC and GyrA targets. A role in low-level ciprofloxacin resistance has also been attributed to efflux systems. To look into ciprofloxacin resistance at a genome-wide scale and to discover additional mutations implicated in resistance, we performed whole-genome sequencing of an S. pneumoniae isolate selected for resistance to ciprofloxacin in vitro (128 μg/ml) and of a clinical isolate displaying low-level ciprofloxacin resistance (2 μg/ml). Gene disruption and DNA transformation experiments with PCR fragments harboring the mutations identified in the in vitro S. pneumoniae mutant revealed that resistance is mainly due to QRDR mutations in parC and gyrA and to the overexpression of the ABC transporters PatA and PatB. In contrast, no QRDR mutations were identified in the genome of the S. pneumoniae clinical isolate with low-level resistance to ciprofloxacin. Assays performed in the presence of the efflux pump inhibitor reserpine suggested that resistance is likely mediated by efflux. Interestingly, the genome sequence of this clinical isolate also revealed mutations in the coding region of patA and patB that we implicated in resistance. Finally, a mutation in the NAD(P)H-dependent glycerol-3-phosphate dehydrogenase identified in the S. pneumoniae clinical strain was shown to protect against ciprofloxacin-mediated reactive oxygen species.

Short-Course Therapy of Gemifloxacin Effective Against Pneumococcal Pneumonia in Mice

Standard 7-14 day (d) courses of antimicrobial therapy for community-acquired pneumonia (CAP) are thought to have contributed to the emergence of resistant pneumoccoci. Consequently, short-course fluoroquinolone regimens have been proposed to minimize resistance. To test this, we examined 2-day versus 5-day regimens of gemifloxacin and levofloxacin for treatment of pneumonia in a murine model. In doing so, we also investigated whether the enhanced potency of gemifloxacin would influence outcomes. CD1 Swiss mice were infected intratracheally with 10(5)-CFU of a virulent Streptococcus pneumoniae strain. Drugs were administered every 8 h for 2 d and 5 d, starting at 24 h postinfection. Temperature was used to assess disease progression. Gemifloxacin remained effective for 2 d and 5 d, with survival rates of 100%-83% compared with 40%-58% for levofloxacin. Eighty-nine to 100% of gemifloxacin-treated mice were clear of pulmonary bacteria compared with only 0%-20% for levofloxacin. For levofloxacin-treated mice, 2 of 7 (29%) isolates with a levofloxacin minimum inhibitory concentration (MIC) 4 times that of the infecting parent strain had ParC mutations. By contrast, no isolates recovered from gemifloxacin-treated mice were reduced in susceptibility. Gemifloxacin could be effective in shortening duration of therapy for CAP treatment as well as minimize resistance development.

The First Steps Towards Fluoroquinolone Resistance in Hungarian Pneumococci

The incidence of fluoroquinolone resistance among Hungarian routine laboratory Streptococcus pneumoniae isolates, collected in 2000-2002, in common with other European countries, was very low; only 5/304 strains (1.64%) were resistant to ciprofloxacin (MIC = 4 microg/ml), and the other fluoroquinolones showed full efficacy. However, we could identify the Lys-137-Asp amino acid change, caused by a point mutation in the QRDR of the parC gene, in five strains. Additionally, we observed a definite shift in the minimum inhibitory concentrations (MICs) of all fluoroquinolones towards higher values throughout the study period. These two findings, coupled with the increasing consumption figures of fluoroquinolones, suggest that pneumococcal resistance looks poised to develop in Hungary.

Comparative antibacterial effects of moxifloxacin and levofloxacin on Streptococcus pneumoniae strains with defined mechanisms of resistance: impact of bacterial inoculum

OBJECTIVES

We aim to further define the impact of the mechanism of fluoroquinolone resistance and inoculum load on the pharmacodynamic effects of levofloxacin and moxifloxacin on Streptococcus pneumoniae.

METHODS

The antibacterial effects of and emergence of resistance (EoR) to moxifloxacin (400 mg once daily) or levofloxacin (750 mg once daily or 500 mg twice daily) were compared using five S. pneumoniae strains containing no known resistance mechanisms, efflux resistance mechanisms, a parC mutation or parC and gyrA mutations, at high (10(8) cfu/mL) and low (10(6) cfu/mL) inocula. An in vitro pharmacokinetic model was used and simulations were performed over 96 h. After drug exposure, isolates were tested for the presence of efflux pumps and mutations in the quinolone resistance-determining regions.

RESULTS

A high inoculum diminished the antibacterial effect of moxifloxacin and levofloxacin. Levofloxacin at both dosages produced EoR with all strains. Levofloxacin regimens with AUC/MIC ratios <100 produced EoR. Moxifloxacin produced EoR with the parC strain only.

CONCLUSIONS

Levofloxacin dosing regimens with low AUC/MIC ratios select for efflux pump overexpression, leading to fluoroquinolone resistance. Levofloxacin dosing may select for gyrA mutations, inducing moxifloxacin resistance. These data confirm that a fluoroquinolone AUC/MIC ratio of >100 is required for prevention of EoR.

Susceptibility of Streptococcus pneumoniae to fluoroquinolones in Canada

Ciprofloxacin, the first fluoroquinolone to be used to treat lower respiratory tract infections (LRTI), demonstrates poor potency against Streptococcus pneumoniae, and its use has been associated with the emergence of resistance. During the last decade, fluoroquinolones with enhanced in vitro activity against S. pneumoniae have replaced ciprofloxacin for the treatment of LRTI. Here, we analyzed the impact of more active fluoroquinolone usage on pneumococci by examining the fluoroquinolone usage, prevalence of fluoroquinolone resistance, and mutations in the genes that encode the major target sites for the fluoroquinolones (gyrA and parC) in pneumococcal isolates collected in Canada-wide surveillance. A total of 26,081 isolates were collected between 1998 and 2009. During this time period, total per capita outpatient use of fluoroquinolones increased from 64 to 96 prescriptions per 1,000 persons per year. The proportion of prescriptions for respiratory tract infection that were for fluoroquinolones increased from 5.9% to 10.7%, but the distribution changed: the proportion of prescriptions for ciprofloxacin decreased from 5.3% to 0.5%, and those for levofloxacin or moxifloxacin increased from 1.5% in 1999 to 5.9% in 2009. The prevalence of ciprofloxacin resistance (MIC ≥ 4 μg/ml), levofloxacin resistance, and moxifloxacin resistance remained unchanged at <2%. Multivariable analyses showed that prevalence of mutations known to be associated with reduced susceptibility to fluoroquinolones did not change during the surveillance period. If fluoroquinolone therapy is required, the preferential use of fluoroquinolones with enhanced pneumococcal activity to treat pneumococcal infections may slow the emergence of resistance in S. pneumoniae.

Fluoroquinolone resistance in Streptococcus dysgalactiae subsp. equisimilis and evidence for a shared global gene pool with Streptococcus pyogenes

Quinolone resistance is an emerging problem in Streptococcus pyogenes, and recombination with Streptococcus dysgalactiae DNA has been implicated as a frequent mechanism leading to resistance. We have characterized a collection of S. dysgalactiae subsp. equisimilis isolates responsible for infections in humans (n = 314) and found a high proportion of levofloxacin-resistant isolates (12%). Resistance was associated with multiple emm types and genetic lineages, as determined by pulsed-field gel electrophoretic profiling. Since we could not find evidence for a role of efflux pumps in resistance, we sequenced the quinolone resistance-determining regions of the gyrA and parC genes of representative resistant and susceptible isolates. We found much greater diversity among the parC genes (19 alleles) than among the gyrA genes (5 alleles). While single mutations in either GyrA or ParC were sufficient to raise the MIC so that the strains were classified as intermediately resistant, higher-level resistance was associated with mutations in both GyrA and ParC. Evidence for recombination with S. pyogenes DNA was found in some parC alleles, but this was not exclusively associated with resistance. Our data support the existence of a common reservoir of genes conferring quinolone resistance shared between S. dysgalactiae subsp. equisimilis and S. pyogenes, while no recombination with the animal pathogen S. dysgalactiae subsp. dysgalactiae could be found.

Characterization of the quinolone resistant determining regions in clinical isolates of pneumococci collected in Canada

BACKGROUND

The objective of this study was to examine Streptococcus pneumoniae isolates collected from a longitudinal surveillance program in order to determine their susceptibility to currently used fluoroquinolones and of the frequency and type of mutations in the quinolone-resistant determining regions (QRDRs) of their parC and gyrA genes.

METHODS

The Canadian Bacterial Surveillance Network has been collecting clinical isolates of S. pneumoniae from across Canada since 1988. Broth microdilution susceptibility testing was carried out according to the Clinical and Laboratory Standards Institute guidelines. The QRDRs of the parC and gyrA genes were sequenced for all isolates with ciprofloxacin MIC > or = 4 mg/L, and a large representative sample of isolates (N = 4,243) with MIC < or = 2 mg/L.

RESULTS

A total of 4,798 out of 30,111 isolates collected from 1988, and 1993 to 2007 were studied. Of those isolates that were successfully sequenced, 184 out of 1,032 with mutations in parC only, 11 out of 30 with mutations in gyrA only, and 292 out of 298 with mutations in parC and gyrA were considered resistant to ciprofloxacin (MIC > or = 4 mg/L). The most common substitutions in the parC were at positions 137 (n = 722), 79 (n = 209), and 83 (n = 56), of which substitutions at positions 79 and 83 were associated with 4-fold increase in MIC to ciprofloxacin, whereas substitutions at position 137 had minimal effect on the ciprofloxacin MIC. A total of 400 out of 622 isolates with Lys-137 parC mutation belonged to serotypes 1, 12, 31, 7A, 9V, 9N and 9L, whereas only 49 out of 3064 isolates with no mutations belonged to these serotypes. Twenty-one out of 30 isolates with substitutions at position 81 of the gyrA gene had an increased MIC to ciprofloxacin. Finally, we found that isolates with mutations in both parC and gyrA were significantly associated with increased MIC to fluoroquinolones.

CONCLUSIONS

Not all mutations, most frequently Lys-137, found in the QRDRs of the parC gene of S. pneumoniae is associated with an increased MIC to fluoroquinolones. The high prevalence of Lys-137 appears to be due to its frequent occurrence in common serotypes.

In vitro activity of garenoxacin against Streptococcus pneumoniae mutants with characterized resistance mechanisms

We evaluated the potency of garenoxacin in selecting resistant Streptococcus pneumoniae mutants by determining its mutant prevention concentration, using strains with and without topoisomerase gene mutations, and compared its potency to that of other quinolones. Garenoxacin had a significantly greater potency against pneumococci, including strains containing topoisomerase mutations. Genetic analysis of the S. pneumoniae mutants created by garenoxacin revealed that the gyrA gene was a primary target of garenoxacin.

Association between fluoroquinolone usage and a dramatic rise in ciprofloxacin-resistant Streptococcus pneumoniae in Canada, 1997-2006

This study evaluated the prevalence of fluoroquinolone usage and investigated the association between usage and resistance in respiratory isolates of Streptococcus pneumoniae in Canada. Fluoroquinolone susceptibility testing was conducted on S. pneumoniae collected from 25 medical centres across Canada over nine study years. Fluoroquinolone prescriptions and consumption figures were derived from data in the IMS Health, Canada CompuScript Audit. Between 1997 and 2006, 11825 S. pneumoniae isolates were collected. Ciprofloxacin resistance rates increased significantly (P<0.01) during the study from 0% to 4.5% in children (0-15 years), from 0.2% to 5.4% in adults (16-64 years) and from 1.4% to 11.6% in the elderly (> or = 65 years). Outpatient ciprofloxacin and respiratory fluoroquinolone prescriptions increased by 55.6% (38.2 prescriptions/1000 population to 59.4 prescriptions/1000 population; P<0.01) and 416.2% (5.3 prescriptions/1000 to 27.4 prescriptions/1000; P<0.01), respectively. Ciprofloxacin and respiratory fluoroquinolone consumption increased by 10.6% [1.1 defined daily doses (DDDs)/1000/day to 1.2 DDDs/1000/day; P=0.02] and 38.2% (0.5 to 0.7 DDDs/1000/day; P=0.02), respectively, from 2001 to 2006. A strong association between ciprofloxacin use and resistance (R(2)=0.89) was identified. Fluoroquinolone resistance in S. pneumoniae increased significantly in Canada from 1997 to 2006 in conjunction with increased ciprofloxacin and respiratory fluoroquinolone consumption. Ciprofloxacin usage appears to be the biggest driver of resistance; however, total fluoroquinolone usage is also important.

Quinolones: action and resistance updated

The quinolones trap DNA gyrase and DNA topoisomerase IV on DNA as complexes in which the DNA is broken but constrained by protein. Early studies suggested that drug binding occurs largely along helix-4 of the GyrA (gyrase) and ParC (topoisomerase IV) proteins. However, recent X-ray crystallography shows drug intercalating between the -1 and +1 nucleotides of cut DNA, with only one end of the drug extending to helix-4. These two models may reflect distinct structural steps in complex formation. A consequence of drug-enzyme-DNA complex formation is reversible inhibition of DNA replication; cell death arises from subsequent events in which bacterial chromosomes are fragmented through two poorly understood pathways. In one pathway, chromosome fragmentation stimulates excessive accumulation of highly toxic reactive oxygen species that are responsible for cell death. Quinolone resistance arises stepwise through selective amplification of mutants when drug concentrations are above the MIC and below the MPC, as observed with static agar plate assays, dynamic in vitro systems, and experimental infection of rabbits. The gap between MIC and MPC can be narrowed by compound design that should restrict the emergence of resistance. Resistance is likely to become increasingly important, since three types of plasmid-borne resistance have been reported.

A unified anti-mutant dosing strategy

Antimicrobial dosing is currently attracting attention as a way to minimize the emergence of resistance. Three dose-based strategies have been advocated, each with shortcomings. Focus on killing susceptible cells overlooks resistant mutant subpopulations that may be present before treatment or generated during therapy; keeping therapeutic drug concentrations above the mutant prevention concentration (MPC; resistant mutant MIC) may be overly stringent; and dosage escalation modelling uses indirect estimates of resistant mutant subpopulation susceptibility (multiples of bulk population susceptibility, MIC) rather than direct estimates from MPC. The latter is significant because MPC and MIC are discordant with multiple pathogen isolates. Combining the strategies leads to MPC-based PK/PD thresholds (e.g. AUC(24)/MPC and t > MPC) for restricting resistant subpopulation enrichment and amplification. Using MPC-based thresholds to model dosing regimens that will restrict emergence of resistance requires generation of databases in which MPC is determined for many isolates.

Pneumococcal antimicrobial resistance: therapeutic strategy and management in community-acquired pneumonia

Streptococcus pneumoniae has been consistently shown to represent the most frequent causative agent of community-acquired pneumonia (CAP) and pneumococcal antibiotic resistance towards different families of antibiotics continues to be a much-debated issue. Microbial resistance causes a great deal of confusion in choosing an empirical treatment for pneumonia and this makes it necessary to know which factors actually determine the real impact of antimicrobial resistance on the outcome of pneumococcal infections. Several different aspects have to be taken into account when analyzing this matter, such as the study design, the condition of the patient at the time of diagnosis, the choice of the initial antimicrobial regimen (combination or monotherapy) and the pharmacokinetic/pharmacodynamic variables of the chosen antibiotic. It is generally accepted that in the treatment of beta-lactam-resistant pneumococcal infections, the use of standard antipneumococcal beta-lactam agents is unlikely to impact negatively on the outcome of CAP when appropriate agents are given in sufficient doses. As a general rule, for infections with penicillin-sensitive strains, penicillin or an aminopenicillin in a standard dosage will be effective; in the cases of strains with intermediate resistance, beta-lactam agents are still considered appropriate treatment although higher dosages are recommended; finally, infections with isolates of high-level penicillin resistance should be treated with alternative agents such as the third-generation cephalosporins or the new antipneumococcal fluoroquinolones. In areas of high prevalence of high-level macrolide resistance, empirical monotherapy with a macrolide is not optimal for the treatment of hospitalised patients with moderate or moderately-severe CAP. Fluoroquinolones are considered to be excellent antibiotics in the treatment of pneumococcal CAP in adults, but their general recommendation has been withheld due to fears of a widespread development of resistance. Most international guidelines recommend combination therapy (beta-lactam plus a macrolide) for the treatment of hospitalised patients with CAP.

In vitro and in vivo antibacterial activities of DC-159a, a new fluoroquinolone

DC-159a is a new 8-methoxy fluoroquinolone that possesses a broad spectrum of antibacterial activity, with extended activity against gram-positive pathogens, especially streptococci and staphylococci from patients with community-acquired infections. DC-159a showed activity against Streptococcus spp. (MIC(90), 0.12 microg/ml) and inhibited the growth of 90% of levofloxacin-intermediate and -resistant strains at 1 microg/ml. The MIC 90s of DC-159a against Staphylococcus spp. were 0.5 microg/ml or less. Against quinolone- and methicillin-resistant Staphylococcus aureus strains, however, the MIC 90 of DC-159a was 8 microg/ml. DC-159a was the most active against Enterococcus spp. (MIC 90, 4 to 8 microg/ml) and was more active than the marketed fluoroquinolones, such as levofloxacin, ciprofloxacin, and moxifloxacin. The MIC 90s of DC-159a against Haemophilus influenzae, Moraxella catarrhalis, and Klebsiella pneumoniae were 0.015, 0.06, and 0.25 microg/ml, respectively. The activity of DC-159a against Mycoplasma pneumoniae was eightfold more potent than that of levofloxacin. The MICs of DC-159a against Chlamydophila pneumoniae were comparable to those of moxifloxacin, and DC-159a was more potent than levofloxacin. The MIC 90s of DC-159a against Peptostreptococcus spp., Clostridium difficile, and Bacteroides fragilis were 0.5, 4, and 2 microg/ml, respectively; and among the quinolones tested it showed the highest level of activity against anaerobic organisms. DC-159a demonstrated rapid bactericidal activity against quinolone-resistant Streptococcus pneumoniae strains both in vitro and in vivo. In vitro, DC-159a showed faster killing than moxifloxacin and garenoxacin. The bactericidal activity of DC-159a in a murine muscle infection model was revealed to be superior to that of moxifloxacin. These activities carried over to the in vivo efficacy in the murine pneumonia model, in which treatment with DC-159a led to bactericidal activity superior to those of the other agents tested.

In vitro pharmacodynamics of moxifloxacin versus levofloxacin against 4 strains of Streptococcus pneumoniae: 1 wild type, 2 first-step parC mutants, and 1 pump mutant

Levofloxacin binds topoisomerase IV, whereas moxifloxacin preferentially binds DNA gyrase. Most 1st-step pneumococcal mutants have alterations in the parC gene of topoisomerase IV. Because of differential binding affinity, moxifloxacin may have superior activity against 1st-step mutants compared with levofloxacin. The purpose of this work was to compare rates and extent of bacterial killing of genetically characterized Streptococcus pneumoniae with moxifloxacin and levofloxacin. Four strains of S. pneumoniae were used: a wild type, 2 first-step parC mutants, and a pump mutant. Using an in vitro pharmacodynamic model run in duplicate, we exposed bacteria to unbound moxifloxacin and levofloxacin peaks of 2 and 4.5 mg/L, respectively, which emulated clinical dosing. Additional experiments were done in which the area under the curve (AUC)/MIC ratio of 1 agent was matched to the competing drug's clinical dose AUC/MIC ratio. Time kill curves were analyzed for rate and extent of bacterial kill and regrowth. Pre- and postexposure MIC and polymerase chain reaction (PCR) testing were done. Moxifloxacin and levofloxacin displayed similar rates and extent of bacterial kill for the wild type, efflux pump type, and parC mutant 27-1361B. Moxifloxacin initially achieved a faster rate of kill, regardless of the AUC/MIC ratio, against parC mutant 7362 (P < 0.05) but not an advantage in time to 3 log kill. Postexposure MIC values were elevated for strain 7362 in 2 moxifloxacin experiments and 1 levofloxacin experiment. Post-PCR analysis revealed new gyrA mutations for all 3 isolates. Both moxifloxacin and levofloxacin are effective against multiple strains of S. pneumoniae.

Characterisation of levofloxacin-resistant clinical isolates of Streptococcus pyogenes in Bilbao, Spain

The resistance mechanisms and clonal relationship were determined for two Streptococcus pyogenes isolates with high-level resistance to levofloxacin as well as to other fluoroquinolones. DNA amplification and sequencing revealed a serine-81-->phenylalanine substitution in GyrA and a double substitution in ParC of serine-79-->phenylalanine and aspartic acid-91-->asparagine. Pulsed-field gel electrophoresis analysis and emm typing determined that both isolates were emm type 28 and were genetically indistinguishable.

Fluoroquinolone resistance in atypical pneumococci and oral streptococci: evidence of horizontal gene transfer of fluoroquinolone resistance determinants from Streptococcus pneumoniae

Atypical strains, presumed to be pneumococcus, with ciprofloxacin MICs of > or =4.0 microg/ml and unique sequence variations within the quinolone resistance-determining regions (QRDRs) of the gyrase and topoisomerase genes in comparison with the Streptococcus pneumoniae R6 strain, were examined. These strains were reidentified using phenotypic methods, including detection of optochin susceptibility, bile solubility, and agglutination by serotype-specific antisera, and genotypic methods, including detection of pneumolysin and autolysin genes by PCR, 16S rRNA sequencing, and multilocus sequence typing (MLST). The analysis based on concatenated sequences of the six MLST loci distinguished the "atypical" strains from pneumococci, and these strains clustered closely with S. mitis. However, all these strains and five of nine strains from the viridans streptococcal group possessed one to three gyrA, gyrB, parC, and parE genes whose QRDR sequences clustered with those of S. pneumoniae, providing evidence of horizontal transfer of the QRDRs of the gyrase and topoisomerase genes from pneumococci into viridans streptococci. These genes also conferred fluoroquinolone resistance to viridans streptococci. In addition, the fluoroquinolone resistance determinants of 32 well-characterized Streptococcus mitis and Streptococcus oralis strains from bacteremic patients were also compared. These strains have unique amino acid substitutions in GyrA and ParC that were distinguishable from those in fluoroquinolone-resistant pneumococci and the "atypical" isolates. Both recombinational events and de novo mutations play an important role in the development of fluoroquinolone resistance.

Detection of parC mutations in Streptococcus pneumoniae by Real-time PCR and Taqman–MGB probes

A Real-time PCR assay was developed by using Taqman-MGB probes to screen mutations at codons Ser79 and Asp83 of Streptococcus pneumoniae parC. One hundred and thirty levofloxacin-susceptible and forty-two levofloxacin-resistant clinical strains were assayed. Mutations at codon 79 were found among all the levofloxacin-resistant strains. Mutations at codon 79 or 83 were found in ten levofloxacin-susceptible strains. This procedure is a reliable method for a rapid detection of mutations in the QRDRs of parC gene of S. pneumoniae and could be carried out in a diagnostic laboratory for some high-risk patients or in epidemiological surveys.

Molecular characterization of increasing fluoroquinolone resistance in Streptococcus pneumoniae isolates in Canada, 1997 to 2005

Molecular characterization of fluoroquinolone-resistant Streptococcus pneumoniae in Canada was conducted from 1997 to 2005. Over the course of the study, 205 ciprofloxacin-resistant isolates were evaluated for ParC and GyrA quinolone resistance-determining region (QRDR) substitutions, substitutions in the full genes of ParC, ParE, and GyrA, reserpine sensitivity, and serotype and by pulsed-field gel electrophoresis. Rates of ciprofloxacin resistance of S. pneumoniae increased significantly, from less than 1% in 1997 to 4.2% in 2005. Ciprofloxacin resistance was greatest in people >64 years of age and least in those <16 years of age. Significant increases were also noted in rates of resistance to gatifloxacin, gemifloxacin, levofloxacin, and moxifloxacin, to the current rates of 1.6%, 1.0%, 1.1%, and 1.0%, respectively. The most common genotype observed consisted of QRDR substitutions in GyrA (Ser81Phe) and ParC (Ser79Phe). Substitutions outside the QRDR of GyrA, ParC, and ParE were not associated with fluoroquinolone resistance in this study. Overall, 21% of isolates were reserpine-sensitive and were thus assumed to be efflux positive. The ciprofloxacin-resistant isolates belonged to 35 different serotypes, but 10 (19F, 11A, 23F, 6B, 22F, 12F, 6A, 14, 9V, and 19A) accounted for 72% of all isolates. The majority of the isolates were found to be genetically unrelated by pulsed-field gel electrophoresis. Within the observed clusters, there was considerable genetic heterogeneity with regard to fluoroquinolone resistance mechanisms and serotypes. Continued surveillance and molecular analysis of fluoroquinolone-resistant S. pneumoniae in Canada are essential for appropriate empirical treatment of infections and early detection of novel resistance mechanisms.

La fenêtre de mutation pour le couple « pneumocoque–fluoroquinolone ». Apport des modèles expérimentaux

Low-level resistance to fluoroquinolones (in vitro susceptible but with topoisomerase mutation, parC) is currently rare among pneumococci in France. However, this resistance is more frequently observed in previously exposed patients and therapeutic failure has been reported. These issues were investigated by using a humanized model of experimental pneumonia induced by pneumococci exhibiting this low-level resistance profile. The results are as follows: 1) when the pneumonia is due to a wild type pneumococcus, humanized ciprofloxacin treatment is not effective because of resistant mutants with parC mutation; moreover, levoflaxin treatment is less bactericidal than gatiflo- or moxifloxacin (-4 vs -6 log CFU/g); 2) when an efflux strain is used, levo-treatment is not efficient but there are no mutants, a gatiflo-treatment is combined when mutants appear and moxiflo-treatment is effective; 3) when the pneumonia is induced with susceptible parC strains, treatment with either levo, or gati, or moxifloxacin is completely ineffective because resistant mutants appear (acquisition of another gyrA mutation). Measure of the mutation prevention concentration (MPC) allows anticipating these results since the mutation window can be determined. These results stress the necessity to identify patients with such pneumococcal strains in order to avoid therapeutic failure and the emergence of fluoroquinolone resistant mutants.

Relative potential for selection of quinolone-resistance-determining-region mutations in Streptococcus pneumoniae by gemifloxacin, gatifloxacin and moxifloxacin

Serial passage of a clinical isolate of Streptococcus pneumoniae, in the presence of moxifloxacin, gatifloxacin or gemifloxacin, gave rise to resistant isolates. Non-susceptibility as defined by Clinical and Laboratory Standards Institute (CLSI, formerly NCCLS) breakpoints arose on Days 10, 11, and 12 with gatifloxacin, gemifloxacin, and moxifloxacin respectively. Moxifloxacin and gatifloxacin selected for a single step quinolone-resistant-determining-region (QRDR) mutation in DNA gyrase (GyrA) on Day 4 and 7 respectively, whereas gemifloxacin selected simultaneously for multi-step mutations in gyrase and topoisomerase IV (ParC) on Day 17 and activated a non-reserpine inhibited efflux mechanism by Day 4. As found in clinical isolates, mutations included Ser-81-Phe and Glu-85-Lys in GyrA and Ser-79-Phe or Asp-83-Tyr in ParC. At high MICs, moxifloxacin showed a previously unreported 4 amino-acid deletion in GyrB as well as a more unusual substitution Ser-79-Leu/Ile in ParC. Gemifloxacin showed a 2- to 16-fold greater activity than moxifloxacin or gatifloxacin against strains with two or more QRDR mutations, however, its potency did not translate to nonsusceptibility and gemifloxacin MIC values were either at or well above the CLSI nonsusceptible breakpoint concentration.

Treating acute exacerbations of chronic bronchitis and community-acquired pneumonia: how effective are respiratory fluoroquinolones?

OBJECTIVE

To provide family physicians with a review of evidence supporting fluoroquinolone therapy for defined patient populations with acute exacerbations of chronic bronchitis (AECB) and community-acquired pneumonia (CAP).

QUALITY OF EVIDENCE

A MEDLINE search found surveillance studies, randomized controlled trials, outcome studies, and expert consensus opinion. Descriptions of patient populations for which fluoroquinolone therapy is recommended are based on level I and level III evidence.

MAIN MESSAGE

A growing body of evidence supports fluoroquinolones as first-choice agents for treatment of AECB or CAP patients with comorbidity or a recent history of antibiotic use. Judicious and targeted therapy using fluoroquinolones among patients at risk of infections of the lower respiratory tract should contribute to improved clinical outcomes and broader health care savings.

CONCLUSION

Current data show clinical utility and cost-effectiveness of fluoroquinolones in lower respiratory tract infections. The most recently issued AECB and CAP guidelines now recommend these antimicrobial agents as first-choice agents for specific patient populations.

Rapid screening of fluoroquinolone resistance determinants in Streptococcus pneumoniae by PCR-restriction fragment length polymorphism and single-strand conformational polymorphism

A rapid method, using PCR-restriction fragment length and single-strand conformation polymorphism (SSCP), was applied to screen for mutations of the fluoroquinolone resistance determinants in Streptococcus pneumoniae. One hundred nonduplicate Streptococcus pneumoniae isolates with ciprofloxacin MICs of > or = 4.0 microg/ml from the Prince of Wales Hospital, Hong Kong, years 2000 to 2003, were examined. For each isolate, PCR amplicons of quinolone resistance-determining regions (QRDRs) of gyrA, gyrB, parC, and parE genes were digested with AluI, HinfI, Sau3AI, and MspI, respectively, and analyzed by SSCP. Each SSCP pattern was given a number, and each isolate obtained a four-digit code, e.g., 1111, that represented the SSCP profile. The SSCP patterns were correlated to mutations characterized from sequence analyses of PCR amplicons. The most common SSCP profile obtained was no. 5232 (40%), which included strains with two amino acid substitutions in the ParC (Lys-137-Asn) and ParE (Ile-460-Val) genes, followed by the SSCP profile 5223 (17%), which included strains with amino acid substitutions in the ParE (Ile-460-Val) gene only. Ten isolates (10%) with amino acid substitutions at GyrA and ParE (+/-ParC) genes were resistant to levofloxacin with a MIC of > or = 16 microg/ml. Other SSCP profiles were unique in distinguishing the common amino acid substitutions in GyrA (Ser-81-Phe) and ParC (Lys-137-Asn, Ser-79-Phe plus Lys-137-Asn, Asp-83-Asn plus Lys-137-Asn, Ser-79-Phe, and Glu-96-Asp). SSCP analysis of restricted fragments generated patterns that were highly discriminative for mutations present in the QRDRs of gyrA, gyrB, parC, and parE. This method provides a database of high resolution profiles on these mutations and allows rapid screening for new mutations of the fluoroquinolone resistance genes.

In vitro activity of DX-619, a novel des-fluoro(6) quinolone, against a panel of Streptococcus pneumoniae mutants with characterized resistance mechanisms

The in vitro activities of DX-619 and four other quinolones were compared against Streptococcus pneumoniae mutants that contained a variety of alterations within the quinolone resistance-determining regions. DX-619 was the most potent quinolone and was least affected by the mutations.

Characterization of fluoroquinolone-resistant beta-hemolytic Streptococcus spp. isolated in North America and Europe including the first report of fluoroquinolone-resistant Streptococcus dysgalactiae subspecies equisimilis: report from the SENTRY Antimicrobial Surveillance Program (1997-2004)

Beta-hemolytic streptococci are common bacterial pathogens that can cause serious invasive disease, and although this group of species has remained susceptible to the fluoroquinolone class, resistant strains have been reported. This multicenter investigation determined the rate of fluoroquinolone-resistant beta-hemolytic streptococci using the SENTRY Antimicrobial Surveillance Program network data (1997-2004). Forty-seven surveillance culture isolates of beta-hemolytic streptococci from North America and Europe with elevated levofloxacin MIC results (2 to >32) microg/mL were tested for susceptibility to other fluoroquinolones including ciprofloxacin, garenoxacin, gatifloxacin, gemifloxacin, and moxifloxacin using reference broth microdilution and Etest (BIODISK, Solna, Sweden) methods. Strains were characterized using polymerase chain reaction and sequencing to detect mutations in the quinolone-resistance determining region (QRDR). The beta-hemolytic streptococci isolates with reduced fluoroquinolone susceptibility included the following Lancefield groups: A (Streptococcus pyogenes; 9 strains), B (Streptococcus agalactiae; 24 strains), C and G (14 strains). Vitek and API 20 strep (bioMerieux, Hazelwood, MO) identification systems, as well as conventional biochemical methods and colony morphology, were used to confirm the organism identifications. The overall potency (MIC90 in microg/mL) for the fluoroquinolones against all tested beta-hemolytic streptococci showed the following rank order: gemifloxacin (0.06) > garenoxacin (0.12) > moxifloxacin (0.25) > gatifloxacin (0.5) > levofloxacin = ciprofloxacin (1). The rate of levofloxacin-resistant beta-hemolytic streptococci in the SENTRY program was 0.14% (Europe) and 0.51% (North America) during the study period. All levofloxacin-resistant strains tested by molecular methods had significant mutations in either parC (position 79 or 83) and/or gyrA (position 81 or 85). All but 2 isolates with high-level resistance to levofloxacin (>32 microg/mL) had gyrA mutations. Strains with lower MIC values to levofloxacin (2-4 microg/mL) only had mutations in parC. The increasing rate of fluoroquinolone-resistant streptococci including Streptococcus pneumoniae, viridans group streptococci, and the more recently reported beta-hemolytic streptococci, is becoming a clinical concern due to the morbidity and mortality caused by these pathogens.

Infrequent occurrence of single mutations in topoisomerase IV and DNA gyrase genes among US levofloxacin-susceptible clinical isolates of Streptococcus pneumoniae from nine institutions (1999–2003)

OBJECTIVES

Prevalence of single quinolone-resistance determining region (QRDR) mutations in Streptococcus pneumoniae was studied from nine institutions over 5 years to track the incidence of single QRDR mutations.

METHODS

All 1106 levofloxacin-susceptible pneumococci (MICs < or = 2.0 mg/L) identified from 1112 total isolates (99.5% susceptibility) in TRUST 3 (1999), TRUST 5 (2001) and TRUST 7 (2003) surveillance studies from the same nine hospitals in nine states were screened for QRDR mutations. Using pyrosequencing, the strains were screened for mutations corresponding to hot spots Asp-78, Ser-79 and Asp-83 in ParC; Asp-80, Ser-81 and Glu-85 in GyrA; Asp-435 in ParE and Asp-435 in GyrB. DNA sequencing of QRDRs was performed to confirm mutations.

RESULTS

No QRDR mutations were found in any of the isolates with levofloxacin MICs < or = 0.5 mg/L and no gyrA or gyrB QRDR mutations were found in any of the screened isolates (MICs < or = 2 mg/L). Four single-step QRDR mutants with the following amino acid substitutions were found: ParE Asp-435 to Asn (isolated in 1999 in Colorado); ParC Asp-83 to Asn (isolated in 2001 in Kentucky); ParC Ser-79 to Phe (isolated in 2003 in Indiana) and ParC Ser-79 to Tyr (isolated in 2003 in California). These non-clonal strains had levofloxacin MICs of 1 mg/L and were non-susceptible to ciprofloxacin (MIC 2-4 mg/L).

CONCLUSIONS

Overall prevalence of single QRDR mutations in levofloxacin-susceptible S. pneumoniae with MICs of < or = 2 mg/L was 0.4% (4/1106) and has remained <1% within nine institutions over 5 years (1999-2003).

Pharmacodynamic evaluation of tosufloxacin against Streptococcus pneumoniae in an in vitro model simulating serum concentration

We compared the antibacterial effects and the emergence of resistance to tosufloxacin or levofloxacin for Streptococcus pneumoniae by simulating the serum concentration according to the Japanese clinical regimens using an in vitro pharmacokinetic-pharmacodynamic model. For quinolone-susceptible strain ATCC49619, tosufloxacin showed bactericidal activity, given that both the AUC(0-24h)/MIC ratios at the dosage of 150 mg t.i.d. and 300 mg b.i.d. of tosufloxacin tosilate were 138 and 193, and the C(max)/MIC ranges were 7.93-10.2 and 15.9-17.6, respectively, which were greater than those of levofloxacin (100 mg t.i.d. and 200 mg b.i.d.). The greater area above the killing curves (AAKCs) or shorter time to achieve 99.9% killing (99.9% KT) in both models of tosufloxacin than those of levofloxacin was related to their larger AUC(0-24h)/MIC and C(max)/MIC. Exposure of only 100 mg t.i.d. of levofloxacin led to outgrowth of the parC mutants, which were twofold less susceptible to levofloxacin than the parent strain. Neither of the tosufloxacin tosilate regimens resulted in isolation of resistant mutants of this strain. For the parC mutant strain D-3197, both the AUC(0-24h)/MIC and C(max)/MIC ratios of tosufloxacin were greater than those of levofloxacin, which resulted in comparable or better bactericidal activity as compared to those of levofloxacin. However, both fluoroquinolones and both regimens led to outgrowth of resistant mutants, which possessed a mutation in gyrA in addition to parC. In conclusion, tosufloxacin is superior to levofloxacin in bactericidal activity against S. pneumoniae in the Japanese clinical regimens, especially in the quinolone-susceptible strain, without emergence of resistant subpopulations.

Failure of levofloxacin treatment in community-acquired pneumococcal pneumonia

Background

Streptococcus pneumoniae is the leading cause of community-acquired pneumonia (CAP). High global incidence of macrolide and penicillin resistance has been reported, whereas fluoroquinolone resistance is uncommon. Current guidelines for suspected CAP in patients with co-morbidity factors and recent antibiotic therapy recommend initial empiric therapy using one fluoroquinolone or one macrolide associated to other drugs (amoxicillin, amoxicillin/clavulanate, broad-spectrum cephalosporins). Resistance to fluoroquinolones is determined by efflux mechanisms and/or mutations in the parC and parE genes coding for topoisomerase IV and/or gyrA and gyrB genes coding for DNA gyrase. No clinical cases due to fluoroquinolone-resistant S. pneumoniae strains have been yet reported from Italy.

Case presentation

A 72-year-old patient with long history of chronic obstructive pulmonary disease and multiple fluoroquinolone treatments for recurrent lower respiratory tract infections developed fever, increased sputum production, and dyspnea. He was treated with oral levofloxacin (500 mg bid). Three days later, because of acute respiratory insufficiency, the patient was hospitalized. Levofloxacin treatment was supplemented with piperacillin/tazobactam. Microbiological tests detected a S. pneumoniae strain intermediate to penicillin (MIC, 1 mg/L) and resistant to macrolides (MIC >256 mg/L) and fluoroquinolones (MIC >32 mg/L). Point mutations were detected in gyrA (Ser81-Phe), parE (Ile460-Val), and parC gene (Ser79-Phe; Lys137-Asn). Complete clinical response followed treatment with piperacillin/tazobactam.

Conclusion

This is the first Italian case of community-acquired pneumonia due to a fluoroquinolone-resistant S. pneumoniae isolate where treatment failure of levofloxacin was documented. Molecular analysis showed a group of mutations that have not yet been reported from Italy and has been detected only twice in Europe. Treatment with piperacillin/tazobactam appears an effective means to inhibit fluoroquinolone-resistant strains of S. pneumoniae causing community-acquired pneumonia in seriously ill patients.

Characterisation of fluoroquinolone-resistant clinical isolates of Streptococcus pyogenes in Barcelona, Spain

Resistance mechanisms and clonal relationships were determined for six Streptococcus pyogenes isolates with low- or high-level ciprofloxacin resistance. Four isolates displayed reduced susceptibility to ciprofloxacin and levofloxacin and had alterations in ParC: Ser80-->Pro (isolate emm3.1); Ser79-->Ala (two isolates emm6.0); and a double substitution Ser79-->Phe and Ala121-->Val (isolate emm12.27). Two isolates (emm12.26) displayed high-level resistance to ciprofloxacin and levofloxacin, as well as to other quinolones. These isolates had the same double substitution in ParC as isolate emm12.27, and an additional substitution (Ser81-->Tyr) in GyrA. Resistance patterns, emm typing and sequencing of the quinolone resistance-determining regions defined two clusters containing three and two isolates, respectively.

Are fluoroquinolone-susceptible isolates of Streptococcus pneumoniae really susceptible? A comparison of resistance mechanisms in Canadian isolates from 1997 and 2003

OBJECTIVES

To assess the prevalence of efflux and amino acid substitutions in ParC and GyrA in Canadian clinical isolates of fluoroquinolone-susceptible Streptococcus pneumoniae with levofloxacin MICs of 1 mg/L collected before the introduction of the respiratory fluoroquinolones (1995-1997) and after 7 years of use (2003).

METHODS

Quinolone resistance determining regions of parC and gyrA were sequenced for 111 clinical isolates collected from 1995 to 1997 and 665 isolates collected in 2003. Efflux was assessed using a reserpine agar dilution method.

RESULTS

No isolates exhibited efflux. No significant increase in isolates harbouring amino acid substitutions was observed over time (0.9% in 1995-1997 to 2.1% in 2003, P = 0.32). However, the proportion of isolates with a ciprofloxacin MIC = 2 mg/L and a levofloxacin MIC = 1 mg/L versus ciprofloxacin MIC = 1 mg/L and a levofloxacin MIC = 1 mg/L increased over time (3.6% to 6.5%, P = 0.0021).

CONCLUSIONS

No increase in prevalence of first-step parC mutations was observed among all fluoroquinolone-susceptible clinical isolates of S. pneumoniae with levofloxacin MICs of 1 mg/L after the introduction of the respiratory fluoroquinolones; however, fluoroquinolones appear to be selecting for isolates with elevated ciprofloxacin MICs.

High genetic diversity of ciprofloxacin-nonsusceptible isolates of Streptococcus pneumoniae in Poland

We have analyzed the susceptibility to ciprofloxacin of 697 pneumococcal isolates collected in 1998-2002 in Poland from patients with respiratory tract diseases. Thirty-one ciprofloxacin-nonsusceptible isolates (MICs, > or =4 microg/ml) were identified, of which two were resistant to levofloxacin (MIC, 8 microg/ml). Serotyping, pulsed-field gel electrophoresis, multilocus sequence typing, and the analysis of resistance determinants showed their great genetic diversity.

Prevalence and characterization of invasive isolates of Streptococcus pyogenes with reduced susceptibility to fluoroquinolones

Fluoroquinolone susceptibility testing was performed on invasive group A streptococcus isolates from 1992-1993 and 2003 from Ontario, Canada. None were nonsusceptible to levofloxacin. Two of 153 (1.3%) from 1992-1993 and 7 of 160 (4.4%) from 2003 had a levofloxacin MIC of 2 mug/ml; all nine had parC mutations, and eight were serotype M6.

Stability of fluoroquinolone resistance in Streptococcus pneumoniae clinical isolates and laboratory-derived mutants

The stability of fluoroquinolone resistance in Streptococcus pneumoniae was evaluated in laboratory-derived mutants and clinical isolates. Isolates with various genotypes and phenotypes were subcultured for 20 days on antibiotic-free media and were monitored by E-tests to identify any alterations in resistance. Fluoroquinolone resistance mechanisms, whether efflux or chromosomally mediated, remained stable in both clinical and laboratory-derived mutants.

Clonal spread of fluoroquinolone non-susceptible Streptococcus pyogenes

BACKGROUND

Fluoroquinolones are an important group of antibiotics widely used in adults, and, despite the absence of official approval, these drugs are also used in children. So far, resistance to fluoroquinolones in Streptococcus pyogenes is very rare.

METHODS

During a national surveillance programme in Belgium from 1999 to 2002, 2793 non-duplicate S. pyogenes recovered from tonsillopharyngitis patients were screened for fluoroquinolone resistance. Mutations in topoisomerase genes and the presence of any efflux pump activity were investigated to elucidate the fluoroquinolone resistance mechanisms. Clonality was assessed by pulsed-field gel electrophoresis (PFGE) and emm typing.

RESULTS

Non-susceptibility to fluoroquinolones, defined as ciprofloxacin MIC > or = 2 mg/L, was identified in 152 (5.4%) of 2793 S. pyogenes. Fifty-five (36%) fluoroquinolone non-susceptible isolates were investigated for known resistance mechanisms; all showed mutations in parC, and 29 (19%) isolates also in parE; antibiotic efflux was not noted. Two major PFGE types comprised 88% of fluoroquinolone non-susceptible S. pyogenes and belonged to serotypes emm6 and emm75. Overall, emm6 and emm75 constituted >90% of all fluoroquinolone non-susceptible isolates and showed a significant temporal and geographical shift within Belgian provinces. Although fluoroquinolone-susceptible S. pyogenes also showed fluctuations in the predominant S. pyogenes serotypes, emm6 or emm75 were under-represented in this population. Approx. 55% of the fluoroquinolone non-susceptible isolates were recovered from children ( < or =16 years).

CONCLUSIONS

We show here, for the first time, a multi-clonal spread of fluoroquinolone non-susceptible S. pyogenes exhibiting a known resistance mechanism. Non-susceptibility to fluoroquinolones in paediatric isolates is of concern.

The Molecular Epidemiology of Streptococcus pneumoniae with Quinolone Resistance Mutations

BACKGROUND

The purpose of this study was to determine the prevalence of fluoroquinolone resistance and quinolone resistance-determining region (QRDR) mutations among Streptococcus pneumoniae isolates in the United States during the period of 2001-2002. A second objective was to examine the genetic relatedness of pneumococcal isolates with parC and/or gyrA mutations during the period of 1994-2002.

METHODS

Susceptibility testing was performed for 1902 S. pneumoniae isolates collected in the United States during the period of 2001-2002. On the basis of the minimum inhibitory concentration (MIC) of ciprofloxacin, 146 isolates were selected from the 2001-2002 study for QRDR analysis of parC, parE, gyrA, and gyrB genes. The genetic relatedness of isolates with parC and/or gyrA mutations from 2001-2002 (n=55) and from 3 US surveillance studies conducted during 1994-2000 (n=56) was determined by pulsed-field gel electrophoresis (PFGE).

RESULTS

Between 1999-2000 and 2001-2002, there was a 2-fold increase in the rate of ciprofloxacin resistance (MIC, >or=4 micro g/mL), from 1.2% to 2.7%, and in the rate of levofloxacin nonsusceptibility (MIC, >or=4 micro g/mL), from 0.6% to 1.3%. The 111 isolates with parC and/or gyrA mutations were assigned to 48 different PFGE types. Forty-four isolates (40%) belonged to 8 PFGE types that were closely related to widespread clones. Fifteen of the 43 levofloxacin-nonsusceptible pneumococci (LNSP) belonged to 4 PFGE types that were closely related to major clones (Spain(23F)-1 [n=6]; Spain(6B)-2 [n=5], Taiwan(19F)-14 [n=2], and Tennessee(23F)-4 [n=2]).

CONCLUSION

The population of fluoroquinolone-resistant S. pneumoniae in the United States has increased but remains genetically diverse. However, 35% of LNSP were related to widespread pneumococcal clones, increasing the potential for the rapid spread of quinolone resistance in this species.

Guide to selection of fluoroquinolones in patients with lower respiratory tract infections

Newer fluoroquinolones such as levofloxacin, moxifloxacin, gatifloxacin and gemifloxacin have several attributes that make them excellent choices for the therapy of lower respiratory tract infections. In particular, they have excellent intrinsic activity against Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis and the atypical respiratory pathogens. Fluoroquinolones may be used as monotherapy to treat high-risk patients with acute exacerbation of chronic bronchitis, and for patients with community-acquired pneumonia requiring hospitalisation, but not admission to intensive care. Overall, the newer fluoroquinolones often achieve clinical cure rates in > or =90% of these patients. However, rates may be lower in hospital-acquired pneumonia, and this infection should be treated on the basis of anticipated organisms and evaluation of risk factors for specific pathogens such as Pseudomonas aeruginosa. In this setting, an antipseudomonal fluoroquinolone may be used in combination with an antipseudomonalbeta-lactam. Concerns are now being raised about the widespread use, and possibly misuse, of fluoroquinolones and the emergence of resistance among S. pneumoniae, Enterobacteriaceae and P. aeruginosa. A number of pharmacokinetic parameters such as the peak concentration of the antibacterial after a dose (C(max)), and the 24-hour area under the concentration-time curve (AUC24) and their relationship to pharmacodynamic parameters such as the minimum inhibitory and the mutant prevention concentrations (MIC and MPC, respectively) have been proposed to predict the effect of fluoroquinolones on bacterial killing and the emergence of resistance. Higher C(max)/MIC or AUC24/MIC and C(max)/MPC or AUC24/MPC ratios, either as a result of dose administration or the susceptibility of the organism, may lead to a better clinical outcome and decrease the emergence of resistance, respectively. Pharmacokinetic profiles that are optimised to target low-level resistant minor subpopulations of bacteria that often exist in infections may help preserve fluoroquinolones as a class. To this end, optimising the AUC24/MPC or C(max)/MPC ratios is important, particularly against S. pneumoniae, in the setting of lower respiratory tract infections. Agents such as moxifloxacin and gemifloxacin with high ratios against this organism are preferred, and agents such as ciprofloxacin with low ratios should be avoided. For agents such as levofloxacin and gatifloxacin, with intermediate ratios against S. pneumoniae, it may be worthwhile considering alternative dose administration strategies, such as using higher dosages, to eradicate low-level resistant variants. This must, of course, be balanced against the potential of toxicity. Innovative approaches to the use of fluoroquinolones are worth testing in further in vitro experiments as well as in clinical trials.

Mutant prevention concentrations for single-step fluoroquinolone-resistant mutants of wild-type, efflux-positive, or ParC or GyrA mutation-containing Streptococcus pneumoniae isolates

Three fluoroquinolone-susceptible and five fluoroquinolone-resistant (two with ParC Ser79Phe mutations, one with a GyrA Ser81Phe mutation, and two that were efflux positive) Streptococcus pneumoniae isolates were exposed to one, two, four, eight, and sixteen times the MICs of ciprofloxacin, gatifloxacin, gemifloxacin, levofloxacin, and moxifloxacin. Mutational frequencies were calculated at each multiple of the MIC for which growth was observed. Mutant prevention concentrations (MPCs) and the multiple of the MIC at the MPC (MP(MIC)) were evaluated. All resulting mutants were sequenced for quinolone resistance-determining region changes in GyrA and ParC and were evaluated for reserpine-sensitive efflux. The MPC order was generally ciprofloxacin > levofloxacin > gatifloxacin > moxifloxacin > gemifloxacin. The MP(MIC) order varied depending on the genetic constitution of the original isolates from which the mutants were generated. For those mutants created from fluoroquinolone-susceptible isolates (those that had wild-type ParC and GyrA and were efflux negative), the MP(MIC) order was ciprofloxacin = moxifloxacin > gemifloxacin > levofloxacin > gatifloxacin. The MP(MIC)s of each fluoroquinolone for mutants created from isolates with a ParC mutation (with wild-type GyrA and efflux negative) were similar. A similar occurrence was observed with the mutants created from the efflux-positive isolates (with wild-type ParC and GyrA). The MP(MIC) order for the mutants created from the isolate with a GyrA mutation (with wild-type ParC and efflux negative) was ciprofloxacin = gemifloxacin > levofloxacin = moxifloxacin > gatifloxacin. Gatifloxacin, levofloxacin, and moxifloxacin may be intrinsically more able to prevent the development of resistance by fluoroquinolone-susceptible isolates, isolates that are efflux positive, or isolates that carry a GyrA mutation. However, once a ParC mutation is present, the MPC increases dramatically for all fluoroquinolones.

Designing fluoroquinolone breakpoints for Streptococcus pneumoniae by using genetics instead of pharmacokinetics-pharmacodynamics

We determined fluoroquinolone microbiological resistance breakpoints for Streptococcus pneumoniae by using genetic instead of pharmacokinetic-pharmacodynamic parameters. The proposed microbiological breakpoints define resistance as the MIC at which >50% of the isolates carry quinolone resistance-determining region mutations and/or, if data are available, when Monte Carlo simulations demonstrate a <90% chance of bacteriological eradication. The proposed microbiological resistant breakpoints are as follows (in micrograms per milliliter): gatifloxacin, >0.25; gemifloxacin, >0.03; levofloxacin, >1; and moxifloxacin, >0.12. Monte Carlo simulations of the once daily 400-mg doses of gatifloxacin and 750-mg doses levofloxacin demonstrated a high level of target attainment (free-drug area under the concentration-time curve from 0 to 24 h/MIC ratio of 30) by using these new genetically derived breakpoints.