Quinolone resistant Haemophilus influenzae

Pharmacokinetics and pharmacodynamics of aerosolized antibacterial agents in chronically infected cystic fibrosis patients

Bacteria adapt to growth in lungs of patients with cystic fibrosis (CF) by selection of heterogeneously resistant variants that are not detected by conventional susceptibility testing but are selected for rapidly during antibacterial treatment. Therefore, total bacterial counts and antibiotic susceptibilities are misleading indicators of infection and are not helpful as guides for therapy decisions or efficacy endpoints. High drug concentrations delivered by aerosol may maximize efficacy, as decreased drug susceptibilities of the pathogens are compensated for by high target site concentrations. However, reductions of the bacterial load in sputum and improvements in lung function were within the same ranges following aerosolized and conventional therapies. Furthermore, the use of conventional pharmacokinetic/pharmacodynamic (PK/PD) surrogates correlating pharmacokinetics in serum with clinical cure and presumed or proven eradication of the pathogen as a basis for PK/PD investigations in CF patients is irrelevant, as minimization of systemic exposure is one of the main objectives of aerosolized therapy; in addition, bacterial pathogens cannot be eradicated, and chronic infection cannot be cured. Consequently, conventional PK/PD surrogates are not applicable to CF patients. It is nonetheless obvious that systemic exposure of patients, with all its sequelae, is minimized and that the burden of oral treatment for CF patients suffering from chronic infections is reduced.

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.

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.

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

The appearance of resistance or reduced susceptibility to fluoroquinolones among Hemophilus influenzae has been documented for nearly a decade. Over this time, the use of fluoroquinolones for the treatment of respiratory infections including commonly isolated bacterial causes of community-acquired infections has markedly increased. The documentation of resistance to fluoroquinolones among Streptococcus pneumoniae and H. influenzae has also become more prevalent as measured by peer-reviewed publications. During 1997-2001, a total of 11,355 H. influenzae isolates were tested by reference broth microdilution methods from strains collected by the SENTRY Antimicrobial Surveillance Program (American and European medical centers). Strains with reduced susceptibility to fluoroquinolones (RSF) were detected during all five study years at an overall rate of 0.15%. Among the tested compounds, sitafloxacin (MIC(50,) 0.03 microg/ml) was the most potent agent against the RSF strains, followed by gemifloxacin (0.12 microg/ml) > garenoxacin = grepafloxacin = levofloxacin = moxifloxacin = trovafloxacin (0.5 microg/ml) > ciprofloxacin = sparfloxacin (1 microg/ml). Gene sequencing of the quinolone resistance determining region and epidemiologic typing of 30 RSF isolates showed diverse mutational events in gyr A and par C and multiple pulsed-field gel electrophoresis (PFGE) patterns among strains that was not consistent with clonal dissemination. Continued surveillance by global or national networks should continue to monitor for H. influenzae isolates that are refractory to fluoroquinolone therapy.

Evaluation of in vitro susceptibility testing criteria for gemifloxacin when tested against Haemophilus influenzae strains with reduced susceptibility to ciprofloxacin and ofloxacin

Although Hemophilus influenzae resistance to fluoroquinolones is low, it is important to monitor the development of populations with decreased susceptibility to this class of antimicrobials. The activity of gemifloxacin, a new fluoroquinolone, was measured against a collection of susceptible wild-type strains (MIC(90,) 0.008 microg/ml for both beta-lactamase-negative and -positive strains) and strains less susceptible to quinolones (MIC(90,) 1 microg/ml). Using a 5microg disk, the gemifloxacin-susceptible strains had MIC results ranging from </= 0.004 to 0.25 microg/ml (the proposed breakpoint), corresponding to zone diameters of 20 to 39 mm. However, some H. influenzae strains having multiple QRDR mutations were less susceptible to gemifloxacin (MIC range, 0.016-2 microg/ml), although gemifloxacin remained active against 57.1% of strains. In vitro testing, using these selected resistant strains, defined the categorical interpretive criteria for routine clinical laboratory use.

Fluoroquinolone-resistant Haemophilus influenzae: frequency of occurrence and analysis of confirmed strains in the SENTRY antimicrobial surveillance program (North and Latin America)

The incidence of fluoroquinolone-resistant (FQR) Haemophilus influenzae and Moraxella catarrhalis isolated from clinical specimens remains very rare, and the identification of such strains has been previously limited to case reports from diverse geographic locations. During the 1997 through 1998 SENTRY Antimicrobial Surveillance Program, four FQR-H. influenzae (0.13% of all strains) and one FQR-M. catarrhalis strains were identified and confirmed as having elevated MICs to > or =5 FQ class drugs. Among H. influenzae strains, MICs to marketed FQs were > or =0.12 microg/ml with ciprofloxacin MIC results > or =8-fold higher than wild type susceptible strains. The FQR-H. influenzae isolates were then compared with two previously reported strains that were determined to be identical using ribotyping and other molecular methods. In contrast, the SENTRY isolates were all genetically distinct and had mutations in parC and/or gyrA. Isolates having the lowest MIC elevations had a single mutation in gyrA, while isolates with higher MICs had at least one mutation in both studied genes. In general, the single gyr A mutations involved the same position but differed in the amino acid substitution (Ser84Leu or Phe or Ala). The isolates reported outside the SENTRY Program (controls) had an unusual mutation in par C (Gly82Asp) and two mutations in gyr A; producing the highest recorded FQR MICs. The FQR-M. catarrhalis strain was discovered in late 1997 and has been reported before. Although detection of these FQR isolates remains at <1% of all contemporary H. influenzae and M. catarrhalis isolates, surveillance programs will be an important detection method to determine the extent of emerging novel resistance patterns among clinically prevalent fastidious pathogens.

Epidemiology of antibiotic resistance in Haemophilus influenzae

During the last 10 years, a continuous increase in the incidence of beta-lactamase-producing Haemophilus influenzae has been observed; in addition, beta-lactamase-negative ampicillin-resistant strains are better identified and more frequently isolated. During the same period, resistance to tetracyclines and chloramphenicol decreased to a very low level. The incidence of resistant bacteria is highly variable according to the site of infection, patient's age, type of Haemophilus, and country or region, according to local epidemiological factors. Follow-up multicenter studies are needed to monitor the evolution of resistance to these antibiotics and also emergence and spread of resistance to other antibiotics, such as new fluoroquinolones, new beta-lactams, and new macrolides.

Antibiotic resistance and prevalence of beta-lactamase in Haemophilus influenzae isolates-a surveillance study of patients with respiratory infection in Saudi Arabia

Haemophilus influenzae was isolated from patients with respiratory tract infections in five centers in Saudi Arabia. All of the 129 isolates tested by MIC agar dilution were fully susceptible to ceftazidime and ciprofloxacin but 13.2% were resistant to ampicillin, 7% to tetracycline, 5.4% to chloramphenicol, 3.9% to roxithromycin, and 1.6% to amoxicillin/clavulanic acid. Seventeen (13.2%) of all isolates produced TEM-1 type beta-lactamase, the majority (82%) characterized as biotype I or II with 4 (23.5%) encapsulated and belonging to serotype b. There was a clear distinction between the prevalence of beta-lactamase production in hospital patients (26.3% of 19 isolates) compared with community based patients (10.9% of 110 isolates). In addition, we report an increase in the prevalence of beta-lactamase negative, ampicillin intermediate strains (BLNAI) compared to previous studies in this defined geographical region. Changes in the frequency and nature of antimicrobial resistance in common respiratory pathogens confirms the need to maintain surveillance.

The in vitro activity of moxifloxacin against Haemophilus influenzae and Moraxella catarrhalis explored using a pharmacodynamic model

OBJECTIVE: To assess the antibacterial action of moxifloxacin on Haemophilus influenzae and Moraxella catarrhalis using an in vitro pharmacodynamic model of infection. METHODS: Serum concentrations in humans associated with doses of 400 mg once a day for 48 h were simulated and the antibacterial effect measured by the log change in viable count at intervals through the simulation compared to time zero and also the area under the bacterial kill curve (AUBKC). Wild-type strains of H. influenzae and M. catarrhalis with varying beta-lactam susceptibilities (moxifloxacin MICs </=0.1 mg/L) and laboratory-generated mutants with moxifloxacin MICs of 0.5-1.0 mg/L were tested. RESULTS: H. influenzae strains with MICs of </=0.06 mg/L were eradicated by 12 h; strains with MICs of 0.5-1.0 mg/L were eradicated by 24-36 h. M. catarrhalis strains with MICs of </=0.08 mg/L were eradicated by 24-36 h, while the less susceptible laboratory mutant (MIC 1.0 mg/L) was not eradicated even at 48 h. Although we used only a single dosing simulation, the AUC/MIC ratio was strongly related to the AUBKC. CONCLUSIONS: These data indicated that once daily dosing of moxifloxacin holds promise for the treatment of infection due to H. influenzae or M. catarrhalis but bacterial killing is related to MIC.

Activities of new fluoroquinolones against fluoroquinolone-resistant pathogens of the lower respiratory tract

The activities of six new fluoroquinolones (moxifloxacin, grepafloxacin, gatifloxacin, trovafloxacin, clinafloxacin, and levofloxacin) compared with those of sparfloxacin and ciprofloxacin with or without reserpine (20 microg/ml) were determined for 19 Streptococcus pneumoniae isolates, 5 Haemophilus sp. isolates, and 10 Pseudomonas aeruginosa isolates with decreased susceptibility to ciprofloxacin from patients with clinically confirmed lower respiratory tract infections. Based upon the MICs at which 50% of isolates were inhibited (MIC50s) and MIC90s, the most active agent was clinafloxacin, followed by (in order of decreasing activity) trovafloxacin, moxifloxacin, gatifloxacin, sparfloxacin, and grepafloxacin. Except for clinafloxacin (and gatifloxacin and trovafloxacin for H. influenzae), none of the new agents had improved activities compared with that of ciprofloxacin for P. aeruginosa and H. influenzae. A variable reserpine effect was observed for ciprofloxacin and S. pneumoniae; however, for 9 of 19 (47%) isolates the MIC of ciprofloxacin was decreased by at least fourfold, suggesting the presence of an efflux pump contributing to the resistance phenotype. The laboratory parC (Ser79) mutant strain of S. pneumoniae required eightfold more ciprofloxacin for inhibition than the wild-type strain, but there was no change in the MIC of sparfloxacin and only a 1-dilution increase in the MICs of the other agents. For efflux pump mutant S. pneumoniae the activities of all the newer agents, except for levofloxacin, were reduced. Except for clinafloxacin, all second-step laboratory mutants required at least 2 microg of all fluoroquinolones per ml for inhibition.

In vitro activity of BAY 12-8039, a novel 8-methoxyquinolone, compared to activities of six fluoroquinolones against Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis

The in vitro activity of a novel 8-methoxyquinolone, BAY 12-8039, against recent clinical isolates of Streptococcus pneumoniae (n = 404), Haemophilus influenzae (n = 330), and Moraxella catarrhalis (n = 250) was evaluated. Activity was compared to those of six other fluoroquinolones: ciprofloxacin, clinafloxacin, levofloxacin, ofloxacin, sparfloxacin and trovafloxacin. BAY 12-8039 and clinafloxacin had the highest levels of activity against S. pneumoniae, both with a MIC at which 90% of the isolates were inhibited (MIC90) of 0.06 microg/ml. Trovafloxacin and sparfloxacin were the next most active agents versus S. pneumoniae (MIC90s = 0.12 microg/ml). No differences in activity against penicillin-susceptible, -intermediate, or -resistant strains of S. pneumoniae were noted for any of the fluoroquinolones tested. MIC90s for the seven fluoroquinolones ranged from 0.008 to 0.06 microg/ml versus H. influenzae and from 0.008 to 0.12 microg/ml for M. catarrhalis. The MICs for two strains of S. pneumoniae and one strain of H. influenzae were noted to be higher than those for the general population of organisms for all of the fluoroquinolones tested. Finally, the activity of BAY 12-8039 versus S. pneumoniae was found to be diminished when MIC determinations were performed with incubation of agar dilution plates or broth microdilution trays in 5 to 7% CO2 versus ambient air.

Can antimicrobial activity be sustained? An appraisal of orally administered drugs used for respiratory tract infections

Respiratory tract infections (RTIs) represent a major cause of illness worldwide. Therefore, it is of great concern that common RTI pathogens have become increasingly resistant to many of the antimicrobial agents used for therapy. For example, Haemophilus influenzae and Moraxella catarrhalis have become resistant to beta-lactam drugs by producing efficient beta-lactamases (> 35 and 90% of strains, respectively). More recently, pneumococci have become more resistant through the mechanism of altered penicillin-binding proteins (PBPs). The rate of penicillin nonsusceptible isolates has risen to > 25% in the United States (1994-1995). It is important to monitor the resistance characteristics of such pathogens and, if possible, to use regionally acquired data to guide empiric selection of therapeutic agents for RTIs. Currently, some antimicrobials remain effective against the majority of these three bacterial species, as exemplified by amoxicillin/clavulanic acid. Furthermore, amoxicillin alone seems to possess greater inhibition than other orally administered beta-lactams at clinically achievable concentrations against pneumococci with altered PBPs. It is critical that steps are taken to limit resistance problems, particularly through; 1) education of prescribers and the public; 2) initiation of the development of novel drugs with alternative modes of action or stability to existing resistance mechanisms; and 3) by continuing to generate quality susceptibility testing data to guide empiric chemotherapy against bacterial pathogens causing RTI.

Results of the Alexander Project: a continuing, multicenter study of the antimicrobial susceptibility of community-acquired lower respiratory tract bacterial pathogens

In 1992, an ongoing, international multicenter study was established to investigate the antimicrobial susceptibility of community-acquired lower respiratory tract bacterial pathogens: the Alexander Project. Isolates cultured from patients living in geographically separated areas, ten in the European Union (EU) and five in the United States (US), were collected and tested using standard methods in a central laboratory. A total of 4,155 isolates of Haemophilus influenzae was collected during the period 1992-1994. beta-lactamase production was the principal mechanism of resistance observed with overall rates in the US (1992 = 26.3%; 1993 = 28.2%; and 1994 = 30.1%) generally twice those seen in the EU (1992 = 12.3%; 1993 = 14.4%; and 1994 = 15.5%). Chloramphenicol resistance was generally low except in Spanish centers where rates ranging from 4.0 to 15.9% were observed during the study period. One thousand one hundred ninety-three isolates of Moraxella catarrhalis were tested. beta-lactamase production was the only mechanism of resistance of any importance detected, with the vast majority of isolates producing the enzyme. Two thousand eight hundred twenty-nine isolates of Streptococcus pneumoniae were tested. French and Spanish centers provided isolates with the highest rates of either low-level (intermediate) or high-level penicillin resistance, which in 1994 ranged from 10.2 to 31.4% and 30.4 to 40.1% for each resistance category, respectively. With the exception of the fluoroquinolones, rates of resistance to other antimicrobials including the macrolides, doxycycline, chloramphenicol, and trimethoprim/sulfamethoxazole were high, generally, in centers with a high prevalence of penicillin resistance. However, in some centers (Toulouse, France and Genoa, Italy) this association was not complete for the macrolides.

Ciprofloxacin-resistant Haemophilus influenzae strains possess mutations in analogous positions of GyrA and ParC

The nucleotide sequences of the quinolone resistance-determining regions of the gyrA and parC genes from five ciprofloxacin-resistant strains of Haemophilus influenzae (MICs, 2 to 32 micrograms/ml) isolated from patients with cystic fibrosis and three ciprofloxacin-susceptible strains of H. influenzae (MICs, < or = 0.1 micrograms/ml) were determined. Four of the five resistant strains possessed at least one amino acid substitution in each of the GyrA and ParC fragments studied. The mutations identified in GyrA were a serine at residue 84 (Ser-84) to Leu or Tyr and Asp-88 to Asn or Tyr. ParC mutations were in positions exactly analogous to those identified in GyrA, namely, Ser-84 to Ile and Glu-88 to Lys. The Glu-88 to Lys ParC substitution was identified only in high-level ciprofloxacin-resistant strains. These mutations have been shown to be the origin of the observed resistance after transformation into ciprofloxacin-susceptible H. influenzae isolates. These results suggest that H. influenzae isolates require at least one amino acid substitution in both GyrA and ParC in order to attain significant levels of resistance to quinolones.

The incidence of respiratory tract pathogens and antimicrobial susceptibilities of Streptococcus pneumoniae, Haemophilus influenzae and Moraxella (Branhamella) catarrhalis isolated between 1990 and 1993

Using a quantitative culture of sputum, the incidence of pathogenic bacteria in respiratory infection in our laboratory between 1990 and 1993 were investigated. While Haemophilus influenzae, Streptococcus pneumoniae and Moraxella (Branhamella) catarrhalis were isolated at high rates (67-78%) from the specimens of outpatients throughout the study period, the incidence of S pneumoniae has increased gradually. The antimicrobial susceptibilities of these three pathogens were examined with the agar dilution method. A marked increase of penicillin (PC) resistant S. pneumoniae (MIC > or = 0.1 microgram/ml) was observed with a resistance rate of 2.1% in 1990 and 25% in 1993. Resistance to erythromycin (EM, MIC > or = 1.56 micrograms/ml) was 8.5% in 1990 but then increased to 34% in 1992. Most of the PC resistant isolates were resistant to multidrugs such as EM, minocycline and clindamycin. The MICs of all beta-lactams examined for S. pneumoniae increased along with the MICs of PC, though the level varied between drugs. The rates of beta-lactamase positive H. influenzae gradually decreased, being 14.3% in 1990 and 7.4% in 1993, whereas those of M. (B) catarrhalis were consistently high (> 90%) every year. In addition to beta-lactamase production, the emergence of strains of H. influenzae and M. (B) catarrhalis resistant to new quinolone drugs should be noted.

Antibiotic susceptibilities of Haemophilus influenzae in central Scotland

OBJECTIVE: To ascertain the incidence of antibiotic resistance in Haemophilus influenzae in central Scotland and the beta-lactamases produced by these isolates. METHODS: A total of 213 H. influenzae isolates from four medical centers in Scotland [Aberdeen (n=58), Edinburgh (n=55), Glasgow (n=64) and Dundee (n=36)] were tested for susceptibility to a range of antimicrobials including beta-lactams, beta-lactam/beta-lactamase-inhibitor combinations, and a representative 4-quinolone, antifolate and macrolide. Susceptibility testing of the beta-lactam/beta-lactamase-inhibitor combination amoxicillin plus clavulanic acid was conducted at both 2:1 and 4:1 ratios and with clavulanic acid fixed at a concentration of 2 mg/L. Each strain was further investigated for the presence of beta-lactamase activity. RESULTS: Although the incidence of resistance to amoxicillin was 15%, in the presence of clavulanic acid, this resistance was reduced to 4.2%, 5.6% and 4.2% with the 2:1 ratio, 4:1 ratio and 2 mg/L fixed concentration, respectively. Sixteen percent of the isolates demonstrated immediate beta-lactamase production. Isoelectric focusing showed that 77.4%, 16.1% and 6.5% of the beta-lactamase-positive strains were found to contain TEM-1, VAT-1 and both TEM-1 and VAT-1 beta-lactamases, respectively. A further 29% of the strains were recognized as being beta-lactamase-positive after prolonged incubation with nitrocephin. CONCLUSIONS: This study suggests that current testing for beta-lactamases may underestimate the prevalence of beta-lactamase production in H. influenzae.

Haemophilus influenzae: then and now

Haemophilus influenzae has long been recognised as a major cause of serious infection and mortality in children less than 5 years old. Prior to the introduction of Haemophilus influenzae type b (Hib) immunisation, the incidence of a child suffering an invasive Haemophilus infection was 20-50/100,000 in industrialised countries and up to ten times higher in developing regions. The introduction of a Hib vaccine programme results in a rapid and dramatic decline in the incidence of Hib infection in the susceptible childhood population. For example, within two years of the introduction of routine Hib vaccination of infants in the UK, the risk of serious Hib infection had fallen from 1:600 to 1:30,000 by 5 years of age. Many other European countries have introduced, or are in the process of introducing, a routine Hib immunisation programme. Because the epidemiology of Haemophilus influenzae infection is changing so dramatically, it is opportune to review Haemophilus influenzae as it was perceived in the pre-vaccine era (the past) and during vaccine implementation (the present), and how its role may change in the post-vaccination era (the future). This review will summarise the historical landmarks that have led to our present-day understanding of Haemophilus influenzae pathogenicity, the concerns about antibiotic resistance, the features of the host immune response to Haemophilus influenzae, and the introduction of the Hib vaccine. Furthermore, the possible importance of this organism in the future will be discussed.

Epidemiology of quinolone resistance: Europe and North and South America

After nearly 10 years of fluoroquinolone usage for a wide range of bacterial infections, a striking difference has been observed in the incidence of bacterial resistance to fluoroquinolones between bacteria responsible for community- and hospital-acquired infections, respectively. Resistance is only rarely encountered among common pathogens. In most studies, 97 to 100% of all pathogens are fully susceptible to fluoroquinolones. In contrast, resistance to fluoroquinolones has emerged and increased among bacteria responsible for nosocomial infections. The incidence of resistance to fluoroquinolones varies between bacterial species, clinical settings and countries, and is related to local epidemic spread of a few clones. The highest incidence of resistance is observed in Pseudomonas aeruginosa, Acinetobacter spp., Serratia marcescens and, particularly, methicillin-resistant Staphylococcus aureus (MRSA): some investigators have reported 95 to 100% fluoroquinolone resistance among MRSA. Follow-up of trends in the resistance to fluoroquinolones based upon surveillance programmes are needed.