Five-year analysis of Haemophilus influenzae isolates with reduced susceptibility to fluoroquinolones: prevalence results from the SENTRY antimicrobial surveillance program

Antimicrobial resistance among Haemophilus influenzae isolates responsible for lower respiratory tract infections in Poland, 2005-2019

Haemophilus influenzae is a human-specific pathogen responsible for respiratory tract infections, meningitis, and sepsis. The study aimed to characterize antibiotic resistance in H. influenzae strains isolated from patients with lower respiratory tract infections over 15 years in Poland. The minimum inhibitory concentrations (MICs) of clinically relevant antibiotics were determined by broth microdilution method. Screening for beta-lactam resistance was performed in all isolates following EUCAST recommendation. Finally, relevant changes in penicillin-binding protein 3 (PBP3) were detected by PCR screening. Of the 1481 isolates collected between 2005 and 2019, 12.6%, 0.2%, 17.1%, and 0.2% were resistant to ampicillin, amoxicillin/clavulanate, cefuroxime, and ceftriaxone, respectively. Among them, 74.4% (1102/1481) of isolates were categorized as BLNAS (β-lactamase negative, ampicillin-susceptible), 13.0% (192/1481) as BLNAS with modified PBP3 (mutations in ftsI gene), 2.6% (39/1481) as BLNAR (β-lactamase negative, ampicillin-resistant), and 0.2% had PBP3 modifications typical for high-BLNAR. Production of β-lactamase characterized 9.7% of isolates (8.6% BLPAR-β-lactamase-positive, ampicillin-resistant, and 1.1% BLPACR-β-lactamase-positive, amoxicillin-clavulanate resistant). Three isolates with PBP3 modifications typical for high-BLNAR proved resistant to ceftriaxone (MIC > 0.125 mg/L). Resistance to ciprofloxacin, chloramphenicol, tetracycline, and trimethoprim-sulfamethoxazole was observed in 0.1%, 0.5%, 1.6%, and 24.7% of isolates, respectively. This is the first report of Polish H. influenzae isolates resistant to third-generation cephalosporins. Polish H. influenzae isolates demonstrate similar susceptibility trends as in many other countries. The substantial proportion of β-lactam-resistant isolates and the emergence of those resistant to third-generation cephalosporins are of great concern and should be under surveillance.

Fluoroquinolone resistance in Haemophilus influenzae from nursing home residents in Taiwan: correlation of MICs and mutations in QRDRs

AIMS

To study the association between number and positions of mutations with MICs of fluoroquinolone non-susceptible Haemophilus influenzae.

METHODS AND RESULTS

More than 40% of 48 H. influenzae isolated from nursing home residents were not susceptible to fluoroquinolone. Amino acid changes in the quinolone resistance determining regions, and correlation with MICs and inhibition zone diameters were analysed. All isolates with reduced susceptibility to fluoroquinolones (MIC ≥0·125 µg ml^-1 ) had at least one mutation in gyrA at position 84 and were resistant to nalidixic acid. Compared to isolates with reduced susceptibility, resistant isolates were associated with mutations in gyrA at positions 88 and 134, and in parC at position 88 (P < 0·001). Inhibition zone diameter for nalidixic acid disk ≥23 mm may detect susceptible isolates.

CONCLUSIONS

Reduced susceptibility to fluoroquinolones was associated with mutations at position 84 in gyrA. A further increase in fluoroquinolone MIC was associated with mutations in gyrA at positions 88 and 134, and parC at position 88.

SIGNIFICANCE AND IMPACT OF THE STUDY

Due to limited resistant H. influenzae strains, prior studies on association between positions of mutations and fluoroquinolone MICs were inconclusive. The comparison of mutations between isolates with susceptibility, reduced susceptibility and high resistance supported the importance of the present study.

Molecular characterization of fluoroquinolones, macrolides, and imipenem resistance in Haemophilus influenzae: analysis of the mutations in QRDRs and assessment of the extent of the AcrAB-TolC-mediated resistance

The aims of the present study were to characterize the mechanisms of resistance to fluoroquinolones, macrolides, and imipenem in Haemophilus influenzae, to assess the extent of the AcrAB-TolC-mediated resistance, and to define a core genome multilocus sequence typing (cgMLST) scheme for H. influenzae by using whole-genome sequencing. Four amino acid substitutions in GyrA (at Ser84 and Asp88), ParC (at Ser84), and ParE (at Asp420) were found to be closely associated to the MICs. We did not find any amino acid substitution surrounding the three highly conserved amino acid motifs in PBP3 related to imipenem resistance. All the isolates possessed the ermB gene. Carbonyl cyanide m-chlorophenylhydrazone (CCCP) decreased the MIC of imipenem by twofold for FQR-6 and fourfold for GE47 and GE88 strains. For erythromycin, the MICs were decreased by twofold. We found that the six FQR isolates were clustered in two groups. The number of different loci within FQR-1_FQR-3_FQR-5 cluster was 6, while FQR-2 and FQR-4 differed for 21 loci. FQR-1_FQR-3_FQR-5 and FQR-2_FQR-4 clusters were distant among each other and compared to 19 genomes downloaded from NCBI, to 8 strains heteroresistant to imipenem, and to 4 strains monoresistant to ciprofloxacin isolated in Denmark. We confirmed that specific amino acid substitutions in GyrA, ParC, and ParE are implicated in quinolone resistance. Additionally, the degree of resistance is related to the number of these amino acid substitutions. We provide robust evidence that drug efflux is one of the substantial mechanisms of imipenem and erythromycin resistance in H. influenzae.

Molecular characterization of fluoroquinolone resistance in nontypeable Haemophilus influenzae clinical isolates

Nontypeable Haemophilus influenzae (NTHi) is a common cause of respiratory infections in adults, who are frequently treated with fluoroquinolones. The aims of this study were to characterize the genotypes of fluoroquinolone-resistant NTHi isolates and their mechanisms of resistance. Among 7,267 H. influenzae isolates collected from adult patients from 2000 to 2013, 28 (0.39%) were ciprofloxacin resistant according to Clinical and Laboratory Standards Institute (CLSI) criteria. In addition, a nalidixic acid screening during 2010 to 2013 detected five (0.23%) isolates that were ciprofloxacin susceptible but nalidixic acid resistant. Sequencing of their quinolone resistance-determining regions and genotyping by pulse-field gel electrophoresis and multilocus sequence typing of the 25 ciprofloxacin-resistant isolates available and all 5 nalidixic acid-resistant isolates were performed. In the NTHi isolates studied, two mutations producing changes in two GyrA residues (Ser84, Asp88) and/or two ParC residues (Ser84, Glu88) were associated with increased fluoroquinolone MICs. Strains with one or two mutations (n = 15) had ciprofloxacin and levofloxacin MICs of 0.12 to 2 μg/ml, while those with three or more mutations (n = 15) had MICs of 4 to 16 μg/ml. Long persistence of fluoroquinolone-resistant strains was observed in three chronic obstructive pulmonary disease patients. High genetic diversity was observed among fluoroquinolone-resistant NTHi isolates. Although fluoroquinolones are commonly used to treat respiratory infections, the proportion of resistant NTHi isolates remains low. The nalidixic acid disk test is useful for detecting the first changes in GyrA or in GyrA plus ParC among fluoroquinolone-susceptible strains that are at a potential risk for the development of resistance under selective pressure by fluoroquinolone treatment.

Evaluation of the kinetics and mechanism of action of anti-integration host factor-mediated disruption of bacterial biofilms

The extracellular polymeric substance produced by many human pathogens during biofilm formation often contains extracellular DNA (eDNA). Strands of bacterial eDNA within the biofilm matrix can occur in a lattice-like network wherein a member of the DNABII family of DNA-binding proteins is positioned at the vertex of each crossed strand. To date, treatment of all biofilms tested with antibodies directed against one DNABII protein, Integration Host Factor (IHF), results in significant disruption. Here, using non-typeable Haemophilus influenzae as a model organism, we report that this effect was rapid, IHF-specific and mediated by binding of transiently dissociated IHF by anti-IHF even when physically separated from the biofilm by a nucleopore membrane. Further, biofilm disruption fostered killing of resident bacteria by previously ineffective antibiotics. We propose the mechanism of action to be the sequestration of IHF upon dissociation from the biofilm eDNA, forcing an equilibrium shift and ultimately, collapse of the biofilm. Further, antibodies against a peptide positioned at the DNA-binding tips of IHF were as effective as antibodies directed against the native protein. As incorporating eDNA and associated DNABII proteins is a common strategy for biofilms formed by multiple human pathogens, this novel therapeutic approach is likely to have broad utility.

A molecular analysis of quinolone-resistant Haemophilus influenzae: validation of the mutations in Quinolone Resistance-Determining Regions

The mechanism of quinolone-resistance is considered to be amino acid mutations in the type II topoisomerase. We validated the genetic mechanisms of quinolone resistance in Haemophilus influenzae. We obtained 29 H. influenzae strains from a nationwide surveillance program in Japan (including 11 quinolone-resistant strains [moxifloxacin: MFLX or levofloxacin MIC ≥2 μg/ml]). We analyzed the sequences of the Quinolone Resistance-Determining Regions (QRDRs) in GyrA, GyrB, ParC and ParE. Furthermore, we induced resistance in susceptible strains by exposing them to quinolone, and investigated the relationship between mutations in the QRDRs and the MICs. Five amino acid substitutions in GyrA (at Ser84 and Asp88) and ParC (at Gly82, Ser84 and Glu88) were found to be closely related to the MICs. The strains with a MFLX MIC of 0.125-1 and 2-4 μg/ml had one and two mutations, respectively. The strains with a MFLX MIC of ≥8 μg/ml had three or more mutations. The strains with induced resistance with MFLX MICs of 0.5-1 and ≥2 μg/ml also had one and two mutations, respectively. We confirmed that these five mutations strongly contribute to quinolone resistance and found that the degree of resistance is related to the number of the mutations. In addition, the three strains of 18 susceptible strains (16.7%) also had a single mutation. These strains may therefore be in the initial stage of quinolone resistance. Currently, the frequency of quinolone-resistant H. influenzae is still low. However, as has occurred with β-lactams, an increase in quinolone use may lead to more quinolone-resistant strains.

Emergence of a multidrug-resistant Haemophilus influenzae strain causing chronic pneumonia in a patient with common variable immunodeficiency

We report the emergence of a multidrug-resistant Haemophilus influenzae strain in a patient with common variable immunodeficiency suffering from recurrent bronchopneumonia caused by H. influenzae. After the patient had received several antibiotic therapies, a strain was isolated showing resistance to ampicillin, ampicillin/sulbactam, cefazolin, cefuroxime, ciprofloxacin, and clarithromycin. Polymerase chain reaction analyses and sequencing revealed the presence of the beta-lactamase gene bla(TEM-1), two mutations (A502T and R517H) in the ftsI gene encoding the transpeptidase region of the penicillin-binding protein 3, and one mutation in the ribosomal protein gene L4 (G65D) conferring resistance to beta-lactams and macrolides, respectively. Additionally, the plasmid-encoded aac(6')-Ib-cr gene mediating slightly reduced susceptibility to quinolones and two mutations in the DNA gyrase gene gyrA and one mutation in the topoisomerase IV gene parC were identified leading to a high-level fluoroquinolone-resistant phenotype. In conclusion, the treatment of H. influenzae infections accompanied by high bacterial loads such as bronchopneumonia can be complicated by the selection of multidrug-resistant strains. Moreover, the emergence of aac(6')-Ib-cr in H. influenzae causing low fluoroquinolone resistance levels might have contributed to the selection of DNA gyrase and topoisomerase IV mutants.

Global fluoroquinolone resistance epidemiology and implictions for clinical use

This paper on the fluoroquinolone resistance epidemiology stratifies the data according to the different prescription patterns by either primary or tertiary caregivers and by indication. Global surveillance studies demonstrate that fluoroquinolone resistance rates increased in the past years in almost all bacterial species except S. pneumoniae and H. influenzae, causing community-acquired respiratory tract infections. However, 10 to 30% of these isolates harbored first-step mutations conferring low level fluoroquinolone resistance. Fluoroquinolone resistance increased in Enterobacteriaceae causing community acquired or healthcare associated urinary tract infections and intraabdominal infections, exceeding 50% in some parts of the world, particularly in Asia. One to two-thirds of Enterobacteriaceae producing extended spectrum β-lactamases were fluoroquinolone resistant too. Furthermore, fluoroquinolones select for methicillin resistance in Staphylococci. Neisseria gonorrhoeae acquired fluoroquinolone resistance rapidly; actual resistance rates are highly variable and can be as high as almost 100%, particularly in Asia, whereas resistance rates in Europe and North America range from <10% in rural areas to >30% in established sexual networks. In general, the continued increase in fluoroquinolone resistance affects patient management and necessitates changes in some guidelines, for example, treatment of urinary tract, intra-abdominal, skin and skin structure infections, and traveller's diarrhea, or even precludes the use in indications like sexually transmitted diseases and enteric fever.

Reduced levofloxacin susceptibility in clinical respiratory isolates of Haemophilus influenzae is not yet associated with mutations in the DNA gyrase and topoisomerase II genes in Korea

Among 155 clinical respiratory isolates of Haemophilus influenzae in Korea, 6 (3.9%) isolates had reduced levofloxacin susceptibility (MICs ≥ 0.5 μg/mL). These six isolates had no significant quinolone resistance-determining region (QRDR) mutations in gyrA, gyrB, parC, or parE. This phenomenon suggests that neither evolution nor spread of any significant QRDRs mutations in clinical isolates occurred in Korea. Therefore, continued surveillance is necessary to observe the evolution of antibiotic-resistance and take measures to avoid the spread of drug-resistant clones.

Antimicrobial activity against Streptococcus pneumoniae and Haemophilus influenzae collected globally between 2004 and 2008 as part of the Tigecycline Evaluation and Surveillance Trial

We report here on the in vitro activity of tigecycline and comparators against a global collection of Streptococcus pneumoniae and Haemophilus influenzae collected between 2004 and 2008 as part of the Tigecycline Evaluation and Surveillance Trial. A total of 6785 S. pneumoniae and 6642 H. influenzae isolates were collected, most from North America. The percentages of penicillin-intermediate resistance and penicillin resistance among S. pneumoniae in North America were 27.8% and 14.3%, respectively. Penicillin resistance ranged from 9.3% in Europe to 25.1% in the Asia-Pacific Rim. The rate of beta-lactamase-producing H. influenzae was 25.8% in North America, and among the other regions, it ranged from 8.7% in South Africa to 26.8% in the Asia-Pacific Rim. Tigecycline MIC(90)'s were 0.03 to 0.12 mg/L and 0.5 to 2 mg/L, depending on the region considered, against S. pneumoniae and H. influenzae, respectively. Tigecycline had low MIC(90)'s against S. pneumoniae and H. influenzae, irrespective of resistance to beta-lactams.

Antimicrobial activities of piperacillin-tazobactam against Haemophilus influenzae isolates, including beta-lactamase-negative ampicillin-resistant and beta-lactamase-positive amoxicillin-clavulanate-resistant isolates, and mutations in their quinolone resistance-determining regions

Beta-lactamase-negative ampicillin-resistant (BLNAR) isolates of Haemophilus influenzae have been emerging in some countries, including Japan. The Clinical and Laboratory Standards Institute has only a susceptible MIC breakpoint (< or = 1 microg/ml) for piperacillin-tazobactam and a disclaimer comment that BLNAR H. influenzae should be considered resistant, which was adapted without presentation of data. In addition, fluoroquinolone-resistant H. influenzae isolates have recently been occasionally reported worldwide. To address these problems, we examined susceptibilities to beta-lactams, including piperacillin-tazobactam, and ciprofloxacin by microdilution and disk diffusion (only for piperacillin-tazobactam) methods, against a total of 400 recent H. influenzae clinical isolates, including 100 beta-lactamase-negative ampicillin-susceptible, beta-lactamase-positive ampicillin-resistant, BLNAR, and beta-lactamase-positive amoxicillin-clavulanate-resistant (BLPACR) isolates each. BLNAR and BLPACR isolates were tested by PCR using primers that amplify specific regions of the ftsI gene. We also detected mutations in quinolone resistance-determining regions (QRDRs) by direct sequencing of the PCR products of DNA fragments. Among beta-lactams, piperacillin-tazobactam exhibited potent activity against all isolates of H. influenzae, with all MICs at < or = 0.5 microg/ml (susceptible). A disk diffusion breakpoint for piperacillin-tazobactam of > or = 21 mm is proposed. We confirmed that all BLNAR and BLPACR isolates had amino acid substitutions in the ftsI gene and that the major pattern was group III-like (87.5%). One ciprofloxacin-resistant isolate (MIC, 16 microg/ml) and 31 ciprofloxacin-susceptible isolates (MICs, 0.06 to 0.5 microg/ml) had amino acid changes in their QRDRs. Piperacillin-tazobactam was the most potent beta-lactam tested against all classes of H. influenzae isolates. It is possible that fluoroquinolone-resistant H. influenzae will emerge since several clinical isolates carried mutations in their QRDRs.

Melting curve analysis for rapid detection of topoisomerase gene mutations in Haemophilus influenzae

We established a real-time PCR assay with melting curve analysis to rapidly genotype quinolone resistance-determining regions (QRDRs) of gyrase A and topoisomerase IV genes in Haemophilus influenzae. This assay is a useful tool for the detection of fluoroquinolone resistance and for the early detection of preexisting QRDR mutations.

Emergence of fluoroquinolone-resistant Haemophilus influenzae strains among elderly patients but not among children

We screened 457 Haemophilus influenzae strains isolated in Japan during 2002 to 2004 and identified 12 fluoroquinolone-resistant strains (2.6%). The resistant strains were divided into three genotypes (eight, three, and one of each type). These were isolated from patients over 58 years of age. Several fluoroquinolone-resistant clones appeared to have invaded the population of elderly patients in a particular area, Sapporo city.

Comparison of azithromycin and moxifloxacin against bacterial isolates causing conjunctivitis

OBJECTIVE

To examine in vitro resistance to azithromycin and moxifloxacin in bacterial conjunctivitis isolates.

METHODS

MIC90s (Minimum Inhibitory Concentration) and resistance rates to azithromycin and moxifloxacin were determined based upon microtiter broth dilution and/or antimicrobial gradient test strips in a multicenter phase III study and confirmed externally.

RESULTS

The most common isolates collected from bacterial conjunctivitis patients in the phase III study were Haemophilus influenzae (40.6%), followed by Staphylococcus epidermidis (19.3%), Propionibacterium acnes (17.3%), Streptococcus pneumoniae (16.8%), and Staphylococcus aureus (0.06%). MIC90s for all of these organisms were well below established resistance breakpoints for moxifloxacin, indicating no bacterial resistance. On the other hand, the MIC90 for H. influenzae was 3-fold higher than the resistance breakpoint for azithromycin, > or = 128-fold higher for S. epidermidis, 16-fold higher for S. pneumoniae and > or = 128-fold higher for S. aureus, indicating moderate to very high bacterial resistance to azithromycin.

CONCLUSIONS

Resistance to azithromycin is more common than resistance to moxifloxacin in clinical isolates causing bacterial conjunctivitis.

Activity of garenoxacin, an investigational des-F(6)-quinolone, tested against pathogens from community-acquired respiratory tract infections, including those with elevated or resistant-level fluoroquinolone MIC values

Garenoxacin, a novel des-F(6)-quinolone, was tested against 40423 pathogenic isolates associated with community-acquired respiratory tract infections (CA-RTIs). The strains included Streptococcus pneumoniae (18887), Haemophilus influenzae (15555), and Moraxella catarrhalis (5981), each isolated from a significant infection monitored by the SENTRY Antimicrobial Surveillance Program (1999-2005; North America, Latin America, and Europe). All tests were performed by reference broth microdilution methods for garenoxacin and 19 comparison agents. The garenoxacin MIC(90) and percentage (%) of strains inhibited at < or =1 microg/mL (proposed susceptible breakpoint) were S. pneumoniae (0.06 microg/mL, >99.9% susceptible), H. influenzae (< or =0.03 microg/mL, >99.9%), and M. catarrhalis (< or =0.03 microg/mL, 100.0%). The garenoxacin potency versus the pneumococci was 16- to 32-fold greater than levofloxacin or ciprofloxacin and 2-fold superior to moxifloxacin (MIC(90), 0.12 microg/mL). Resistances to other classes of antimicrobials did not adversely influence garenoxacin MIC results. Ciprofloxacin- or levofloxacin-resistant (MIC, > or =4 microg/mL) S. pneumoniae had higher garenoxacin MIC(90) values (1 microg/mL), but 90.6% to 97.5% of strains remained susceptible. Strains of all 3 monitored pathogens with mutations in the quinolone resistance determining region (QRDR) had higher garenoxacin MIC results, with > or =3 to 4 QRDR mutations required to elevate garenoxacin MIC values to > or =2 microg/mL. In conclusion, garenoxacin possesses a potent activity against pneumococci, H. influenzae, and M. catarrhalis strains worldwide, at a level significantly greater than the available tested agents in the fluoroquinolone class (ciprofloxacin, levofloxacin, and moxifloxacin). Only 13 and 4 isolates (0.07% and 0.03%) of S. pneumoniae and H. influenzae, respectively, had a garenoxacin MIC at > or =2 microg/mL, thus, making this new "respiratory antipneumococcal" quinolone an attractive candidate for the therapy of contemporary CA-RTI (bronchitis, pneumonia, and sinusitis).

Garenoxacin activity against isolates form patients hospitalized with community-acquired pneumonia and multidrug-resistant Streptococcus pneumoniae

Community-acquired pneumonia (CAP) continues to cause significant morbidity worldwide, and the principal bacterial pathogens (Streptococcus pneumoniae and Haemophilus influenzae) have acquired numerous resistance mechanisms over the last few decades. CAP treatment guidelines have suggested the use of broader spectrum agents, such as antipneumococcal fluoroquinolones as the therapy for at-risk patient population. In this report, we studied 3087 CAP isolates from the SENTRY Antimicrobial Surveillance Program (1999-2005) worldwide and all respiratory tract infection (RTI) isolate population of pneumococci (14665 strains) grouped by antibiogram patterns against a new des-F(6)-quinolone, garenoxacin. Results indicated that garenoxacin was highly active against CAP isolates of S. pneumoniae (MIC(90), 0.06 microg/mL) and H. influenzae (MIC(90), < or =0.03 microg/mL). This garenoxacin potency was 8- to 32-fold greater than gatifloxacin, levofloxacin, and ciprofloxacin against the pneumococci and >99.9% of strains were inhibited at < or =1 microg/mL (proposed susceptible breakpoint). Garenoxacin MIC values were not affected by resistances among S. pneumoniae strains to penicillin or erythromycin; however, coresistances were high among the beta-lactams (penicillins and cephalosporins), macrolides, tetracyclines, and trimethoprim/sulfamethoxazole. Analysis of S. pneumoniae isolates with various antimicrobial resistance patterns to 6 drug classes demonstrated that garenoxacin was active against >99.9% (MIC, < or =1 microg/mL) of strains, and the most resistant pneumococci (6-drug resistance, 1051 strains or 7.2% of all isolates) were completely susceptible (100.0% at < or =1 microg/mL) to garenoxacin (MIC(90), 0.06 microg/mL). These results illustrate the high activity of garenoxacin against contemporary CAP isolates and especially against multidrug-resistant (MDR) S. pneumoniae that have created therapeutic dilemmas for all RTI presentations. Garenoxacin appears to be a welcome addition to the CAP treatment options, particularly for the emerging MDR pneumococci strains.

Diversity of ampicillin resistance genes and antimicrobial susceptibility patterns in Haemophilus influenzae strains isolated in Korea

By Etest determination of the susceptibilities of 229 Haemophilus influenzae strains isolated in Korea to 10 antibiotics, the isolates were found to be antibiotic nonsusceptible in the following order: ampicillin (58.1%), trimethoprim-sulfamethoxazole (52%), cefaclor (41.1%), clarithromycin (25.8%), chloramphenicol (14.0%), amoxicillin-clavulanic acid (13.5%), meropenem (11.7%), cefixime (10.9%), cefuroxime (9.2%), and levofloxacin (1.3%). The prevalences of each resistance class were 23.6% for beta-lactamase-negative ampicillin-susceptible (BLNAS) strains; 37.6% for strains with the TEM-1 type beta-lactamase gene; 1.3% for strains with the ROB-1 type beta-lactamase gene; 29.3% for the beta-lactamase-negative ampicillin-resistant (BLNAR) strains with a mutation in the ftsI gene, which encodes PBP 3; and 8.3% for beta-lactamase-positive amoxicillin-clavulanate-resistant (BLPACR) strains, which showed both resistance mechanisms (i.e., a beta-lactamase gene and a mutation in the ftsI gene). The MIC50s of all beta-lactams, including cephem and meropenem agents, for the BLNAR strains were two to three times higher than those for the BLNAS strains. This study confirms that the prevalence of BLNAR and BLPACR strains is relatively high and for the first time confirms the presence of H. influenzae strains carrying blaROB-1 in Korea. Even though mutations in another gene(s) might be involved in beta-lactam resistance, these results suggest that mutations in the ftsI gene are important for the development of resistance to beta-lactams in H. influenzae strains in Korea.

Activities of ceftobiprole, a novel broad-spectrum cephalosporin, against Haemophilus influenzae and Moraxella catarrhalis

Ceftobiprole, a broad-spectrum pyrrolidinone-3-ylidenemethyl cephem currently in phase III clinical trials, had MICs between 0.008 microg/ml and 8.0 microg/ml for 321 clinical isolates of Haemophilus influenzae and between < or =0.004 microg/ml and 1.0 microg/ml for 49 clinical isolates of Moraxella catarrhalis. Ceftobiprole MIC(50) and MIC(90) values for H. influenzae were 0.06 microg/ml and 0.25 microg/ml for beta-lactamase-positive strains (n = 262), 0.03 microg/ml and 0.25 microg/ml for beta-lactamase-negative strains (n = 40), and 0.5 microg/ml and 2.0 microg/ml for beta-lactamase-negative ampicillin-resistant strains (n = 19), respectively. Ceftobiprole MIC(50) and MIC(90) values for beta-lactamase-positive M. catarrhalis strains (n = 40) were 0.12 microg/ml and 0.5 microg/ml, respectively, whereas the ceftobiprole MIC range for beta-lactamase-negative M. catarrhalis strains (n = 9) was < or =0.004 to 0.03 microg/ml. Ceftriaxone MICs usually were generally at least twofold lower than those of ceftobiprole, whereas amoxicillin-clavulanate MICs usually were higher than those of ceftobiprole. Azithromycin and telithromycin had unimodal MIC distributions against H. influenzae, with MIC(90) values of azithromycin and telithromycin of 2 microg/ml and 4 microg/ml, respectively. Except for selected quinolone-nonsusceptible H. influenzae strains, moxifloxacin proved highly active, with MIC(90) values of 0.12 microg/ml. Time-kill analyses showed that ceftobiprole, ceftriaxone, cefpodoxime, amoxicillin-clavulanate, azithromycin, telithromycin, and moxifloxacin were bactericidal at 2x MIC by 24 h against all 10 H. influenzae strains surveyed. Only modest increases in MICs were found for H. influenzae or M. catarrhalis clones after 50 serial passages in the presence of subinhibitory concentrations of ceftobiprole, and single-passage selection showed that the selection frequency of H. influenzae or M. catarrhalis clones with elevated ceftobiprole MICs is quite low.

Gemifloxacin for the treatment of respiratory tract infections: in vitro susceptibility, pharmacokinetics and pharmacodynamics, clinical efficacy, and safety

Gemifloxacin is a synthetic fluoroquinolone antimicrobial agent exhibiting potent activity against most gram-negative and gram-positive organisms, such as the important community-acquired respiratory pathogens Streptococcus pneumoniae (including multidrug-resistant S. pneumoniae), Haemophilus influenzae , and Moraxella catarrhalis . The agent's mechanism of action involves dual targeting of two essential bacterial enzymes: DNA gyrase and topoisomerase IV. Gemifloxacin was approved by the Food and Drug Administration in April 2003 for treatment of community-acquired pneumonia and acute bacterial exacerbation of chronic bronchitis. The drug has an oral bioavailability of approximately 71%. Approximately 20-35% of gemifloxacin is excreted unchanged in the urine after 24 hours. The elimination half-life of gemifloxacin is 6-8 hours in patients with normal renal function, supporting once-daily dosing. The 24-hour free-drug area under the plasma concentration-time curve:minimum inhibitory concentration ratio (fAUC(0-24):MIC) associated with efficacy, based on results from in vitro and animal models of infection, is approximately 30. With a mean fAUC(0-24) of approximately 3 microg*hour/ml (35% of total AUC(0-24) of 8.4) and a median S. pneumoniae MIC for 90% of tested strains of 0.03, a fAUC(0-24):MIC ratio of 100 would be expected after standard dosing (320 mg once/day). In clinical studies involving both hospitalized and outpatient populations, gemifloxacin has been highly effective in the treatment of community-acquired pneumonia and acute exacerbation of chronic bronchitis. Clinical success rates ranged from 93.9-95.9% in patients with community-acquired pneumonia and 96.1-97.5% in those with acute exacerbation of chronic bronchitis. Gemifloxacin is well tolerated; the frequency of adverse events with this agent is low. Most adverse events are mild-to-moderate in severity, with diarrhea (< 4%), nausea and rash (< 3%), and headache (< 2%) most commonly reported. Drug interactions with gemifloxacin are not common, although absorption is greatly reduced when given with divalent and trivalent cation-containing compounds, such as antacids. Due to its potent activity against many common gram-positive and gram-negative respiratory pathogens, its proven clinical efficacy, and its favorable safety profile, gemifloxacin is a highly effective empiric treatment for community-acquired lower respiratory tract infections.

Decreased levofloxacin susceptibility in Haemophilus influenzae in children, Hong Kong

Among 563 strains of Haemophilus influenzae from young children in Hong Kong, 5 (0.9%) had decreased susceptibility to quinolones. The five strains had a Ser-84-Lys or Asp-88-Asn substitution in GyrA. Pulsed-field gel electrophoresis showed that the isolates are genetically diverse.

Decreasing prevalence of beta-lactamase production among respiratory tract isolates of Haemophilus influenzae in the United States

A total of 986 isolates of Haemophilus influenzae from patients with respiratory tract infections in 45 United States medical centers were characterized during the winter of 2002-2003. beta-Lactamase production was noted with 26.2% of isolates; 14.6% were resistant to trimethoprim-sulfamethoxazole. Resistance to other relevant antimicrobial agents was extremely uncommon. In comparison to the results of four previous national surveys conducted since 1994, the prevalence of beta-lactamase production with this pathogen appears to be decreasing.

Novel Ser79Leu and Ser81Ile substitutions in the quinolone resistance-determining regions of ParC topoisomerase IV and GyrA DNA gyrase subunits from recent fluoroquinolone-resistant Streptococcus pneumoniae clinical isolates

Resistance of Streptococcus pneumoniae to fluoroquinolones is caused predominantly by amino acid substitutions at positions Ser79 of ParC and Ser81 of GyrA to either Phe or Tyr encoded in the quinolone resistance-determining regions of the parC topoisomerase IV and gyrA DNA gyrase genes. Analysis of highly resistant clinical isolates identified novel second-step substitutions, Ser79Leu (ParC) and Ser81Ile (GyrA). To determine contributions of these new mutations to fluoroquinolone resistance either alone or in combination with other Ser79/81 alleles, the substitutions Ser79Leu/Phe/Tyr in ParC and Ser81Ile/Phe/Tyr in GyrA were introduced into the R6 background, resulting in 15 isogenic strains. Their level of fluoroquinolone resistance was determined by susceptibility testing for ciprofloxacin, levofloxacin, moxifloxacin, gatifloxacin, gemifloxacin, garenoxacin, and norfloxacin. Leu79 and Ile81 alone as well as 79/81Phe/Tyr substitutions did not contribute significantly to resistance, with fluoroquinolone MICs increasing two- to fourfold compared to wild type for all agents tested. Fluoroquinolone MICs for double transformants ParC Ser79Phe/Tyr/Leu-GyrA Ser81Phe/Tyr were uniformly increased by 8- to 64-fold regardless of pairs of amino acid substitutions. However, combinations including Ile81 conferred two- to fourfold-higher levels of resistance than did combinations including any other Ser81 GyrA substitution, thus demonstrating the differential effects of diverse amino acid substitutions at particular hotspots on fluoroquinolone MICs.

Quinolone-resistant Haemophilus influenzae: determination of mutant selection window for ciprofloxacin, garenoxacin, levofloxacin, and moxifloxacin

Stepwise selection of ciprofloxacin-resistant Haemophilus influenzae mutants produced first-, second-, third-, and fourth-step substitutions in GyrA (S84Y), ParC (S84R), GyrA (D88N), and ParC (E88K), respectively. Successive mutations raised the mutant selection window. The wild-type selection window for garenoxacin, levofloxacin, and moxifloxacin was also measured.

A randomized, double-blind study comparing 5 days oral gemifloxacin with 7 days oral levofloxacin in patients with acute exacerbation of chronic bronchitis

OBJECTIVE

To demonstrate that 5 days of treatment with a new fluoroquinolone, gemifloxacin, is at least as effective as 7 days of treatment with levofloxacin in adult patients with acute exacerbation of chronic bronchitis (AECB).

DESIGN

Randomized, double-blind, double dummy, multicentre, parallel group study

SETTING

Sixty different medical centers in US, UK and Germany.

MATERIAL AND METHODS

A total of 360 adults (>40 years of age) with AECB were randomly assigned to receive gemifloxacin 320 mg once daily for 5 days or levofloxacin 500mg once daily for 7 days. The primary efficacy parameter was a clinical response at follow-up (Days 14-21).

RESULTS

In total, 335/360 patients completed the study (93.1%). Seven patients receiving gemifloxacin withdrew from the study compared to 18 patients receiving levofloxacin; this difference was statistically significant (Fisher's exact test: p=0.02). In the intent-to-treat (ITT) population, the clinical success rate at follow-up (Days 14-21) was 85.2% (155/182) with gemifloxacin and 78.1% (139/178) with levofloxacin. Clinical success rate in the per-protocol (PP) population was 88.2% (134/152) with gemifloxacin and 85.1% (126/148) with levofloxacin. At long-term follow-up (Days 28-35), the clinical success rates in the PP population were 83.7% (123/147) with gemifloxacin and 78.4% (109/139) with levofloxacin. The difference in success rates was 5.26% (95% CI: -3.83, 14.34).

CONCLUSION

The clinical efficacy of gemifloxacin 320 mg once daily for 5 days in AECB was at least as good as levofloxacin 500 mg once daily for 7 days. Fewer withdrawals and superior clinical efficacy at long-term follow-up were also seen with gemifloxacin.

Quinolone-resistant Haemophilus influenzae in a long-term-care facility: nucleotide sequence characterization of alterations in the genes encoding DNA gyrase and DNA topoisomerase IV

Fluoroquinolone-resistant isolates of Haemophilus influenzae, obtained from a long-term care facility, were examined for nucleotide sequence differences in the quinolone-resistance-determining regions of gyrA, gyrB, parC, and parE. Similarities among the resistant isolates, plus multiple differences with susceptible isolates, suggest clonal dissemination involving two resistant subclones.

In vitro selection of resistance in haemophilus influenzae by 4 quinolones and 5 beta-lactams

We tested abilities of ciprofloxacin, levofloxacin, gatifloxacin, moxifloxacin, amoxicillin, amoxicillin/clavulanate, cefixime, cefpodoxime, and cefdinir to select resistant mutants in 5 beta-lactamase positive and 5 beta-lactamase negative Haemophilus influenzae strains by single and multistep methodology. In multistep tests, amoxicillin, amoxicillin/clavulanate and cefpodoxime exposure did not cause >4-fold minimum inhibitory concentration (MIC) increase after 50 days. One mutant selected by cefdinir had one amino acid substitution (Gly490Glu) in PBP3 and became resistant to cefdinir. Cefixime exposure caused 8-fold MIC-increase in 1 strain with TEM but the mutant remained cefixime susceptible and had no alteration in PBP3 or TEM. Among 10 strains tested, ciprofloxacin, moxifloxacin, gatifloxacin, levofloxacin caused >4-fold MIC increase in 6, 6, 5, and 2 strain, respectively. Despite the increases in quinolone MICs, none of the mutants became resistant to quinolones by established criteria. Quinolone selected mutants had quindone resistance-determining region (QRDR) alterations in GyrA, GyrB, ParC, ParE. Four quinolone mutants had no QRDR alterations. Among beta-lactams cefdinir and cefixime selected one mutant each with higher MICs however amoxicillin, amoxicillin/clavulanate, and cefpodoxime exposure did not select resistant mutants.

Quinolone-Resistant Haemophilus influenzae in a Long-Term Care Facility: Clinical and Molecular Epidemiology

We describe a clonal outbreak of quinolone-resistant Haemophilus influenzae (QRHI) from an affiliated long-term care facility (LTCF-A); the outbreak was associated with the clinical use of levofloxacin, which was determined to be a risk factor for acquisition of QRHI. The minimum inhibitory concentration to which 90% of isolates were susceptible (MIC90), as determined by broth microdilution, was >4 microg/mL for levofloxacin, >2 microg/mL for moxifloxacin, >2 microg/mL for gatifloxacin, and 8 microg/mL for gemifloxacin. The MIC90, as determined by Etest (AB Biodisk), was >32 microg/mL for levofloxacin, ciprofloxacin, moxifloxacin, and gatifloxacin. Having been a resident at LTCF-A and having chronic obstructive pulmonary disease were significant risk factors for acquisition of QRHI at our 500-bed hospital (New York Hospital Queens). All QRHI isolates were found to be genetically related by pulsed-field gel electrophoresis, were nontypeable, were susceptible to ceftriaxone and azithromycin, and were negative for beta -lactamase production. Emphasis on patient contact and respiratory isolation and placing colonized or infected patients in cohorts yielded a marked reduction in the prevalence of QRHI at LTCF-A.

Comparison of Streptococcus pneumoniae and Haemophilus influenzae susceptibilities from community-acquired respiratory tract infections and hospitalized patients with pneumonia: five-year results for the SENTRY Antimicrobial Surveillance Program

The SENTRY Antimicrobial Surveillance Program has been monitoring the activity of commonly prescribed and novel antimicrobial agents on a global scale from 1997 to the present. Specific objectives have documented the key resistance rates among pathogens from both patients hospitalized with pneumonia and those diagnosed with community-acquired pneumonia. Hemophilus influenzae and Streptococcus pneumoniae are common pathogens in both of these patient populations and the susceptibility profiles for these two species were compared to distinguish potential differences that may be evident in North American surveillance (1997-2001). A total of 6,515 isolates of S. pneumoniae and 6,726 H. influenzae strains were tested using reference broth microdilution methods at a monitoring center. Ampicillin resistance was approximately 25% among H. influenzae isolates and did not significantly differ between strains from community-acquired infections or hospitalized patients. beta-lactamase-negative ampicillin resistant strains and fluoroquinolone refractory strains were rare (0.3 and </= 0.2%, respectively) and the former only detected among hospitalized patients. Macrolide-resistant H. influenzae was most prevalent in hospitalized patients with pneumonia (24.4% for clarithromycin). In contrast, H. influenzae isolates from community-acquired infections were less susceptible (78.6-81.7%) to trimethoprim/sulfamethoxazole, but very susceptible to fluoroquinolones (99.9-100.0%). The community-acquired S. pneumoniae isolates were generally more resistant to penicillin (16.7%) and other beta-lactams compared to those from hospitalized patients (12.1%), and were also much more resistant to trimethoprim/sulfamethoxazole (25.0%) compared to inpatient isolates (6.7%). In contrast, isolates with reduced fluoroquinolone susceptibility or resistance were more common among hospitalized patients (ciprofloxacin resistance at 4.0%) and increased over the five monitored years. It is evident from this longitudinal study that some antimicrobial agents are becoming less efficacious against common respiratory tract pathogens depending on the clinical setting and surveillance of resistance appears to be a prudent practice.