Clinical Isolates Of Haemophilus Influenzae Research Articles

In vitro activity of cefpodoxime against Russian clinical isolates of Haemophilus influenzae, Streptococcus pneumoniae and Streptococcus pyogenes

Objective. To determine in vitro activity of oral III generation cephalosporin cefpodoxime against clinical isolates of Haemophilus influenzae, Streptococcus pneumoniae and Streptococcus pyogenes isolated from patients with community-acquired respiratory tract infections in different regions of the Russian Federation. Materials and Methods. The study included isolates of bacterial pathogens of community-acquired respiratory tract infections isolated from outpatients and hospitalized patients in different regions of the Russian Federation. A total of 558 isolates were included in the study, including 184 isolates of H. influenzae, 186 isolates of S. pneumoniae and 188 isolates of S. pyogenes. Species identification was performed using the MALDI-TOF mass spectrometry (Bruker Daltonics, Germany), for S. pneumoniae identification was also performed taking into account the morphology of colonies on blood agar, the presence of α-hemolysis, negative catalase reaction, sensitivity to optochin and positive results of latex-agglutination using DrySpot kit (OXOID, UK). Antimicrobial susceptibility to cefpodoxime and comparative antimicrobials was determined using broth microdilution method; interpretation of susceptibility testing results was performed in accordance with the recommendations of EUCAST, v.13.0. Data analysis and visualization were performed using the online platform AMRcloud. Results. Despite the generally low incidence of antibiotic resistance in the tested H. influenzae isolates, cefpodoxime, to which all tested isolates were susceptible, was superior to all other oral antibiotics in terms of in vitro activity: aminophenocillins (R – 8.7%), amoxicillin/clavulanate (R – 1.1%), co-trimoxazole (R – 31.5%), levofloxacin (R – 3.8%), moxifloxacin (R – 3.8%), tetracycline (R – 11%), cefixime (R – 2.2%), ceftibuten (R – 3.3%). Among the studied S. pneumoniae isolates, 81.7% were susceptible to cefpodoxime. All isolates resistant to penicillin, amoxicillin and ceftriaxone were also resistant to cefpodoxime. Cefpodoxime was inferior to levofloxacin (R – 0%), moxifloxacin (R – 0%), linezolid (R – 0%), vancomycin (R – 0%), ertapenem (R – 8.6%), ceftaroline (R – 2.3%), and chloramphenicol (R – 3.2%) in terms of in vitro activity against S. pneumoniae. However, all these drugs are either not available in oral form or have a less favorable safety profile compared to cefpodoxime. When compared with other III generation oral cephalosporins cefixime and ceftibuten, the activity of cefpodoxime against S. pneumoniae was significantly higher based on MIC50/90 values (cefixime – 0.125⁄8 mg/l, ceftibuten – 2/≥ 128 mg/l, cefpodoxime – 0.06/4 mg/l) and MICs range (cefixime – 0.06/≥ 128 mg/l, ceftibuten – 0.06/≥ 128 mg/l, cefpodoxime – 0.03/32 mg/l). No strains resistant to β-lactam antibiotics were detected among the tested S. pyogenes isolates. Based on the MIC50/90 values and the range of MIC values, the in vitro activity of cefpodoxime was higher than that of ceftibuten and comparable to that of cefixime. Conclusions. According to the results of our study, as well as in view of its pharmacokinetic profile, high safety and compliance, cefpodoxime can be considered as one of the options for oral therapy of community-acquired bacterial upper and lower respiratory tract infections.

In vitro activity of thiamphenicol against Haemophilus influenzae, Streptococcus pneumoniae and Streptococcus pyogenes clinical isolates

Objective. To determine in vitro activity of thiamphenicol and other clinically available antimicrobials against clinical isolates of Haemophilus influenzae, Streptococcus pneumoniae and Streptococcus pyogenes. Materials and Methods. We included in the study 875 clinical isolates from 20 Russian cities during 2018–2019. Among tested strains, 126 were H. influenzae, 389 – S. pneumoniae, 360 – S. pyogenes. Antimicrobial susceptibility testing was performed using broth microdilution method according to ISO 20776-1:2006. AST results were interpreted according to EUCAST v.11.0 clinical breakpoints. Results. The minimum inhibitory concentrations (MICs) of thiamphenicol did not exceed 2 mg/L for 94.4% of H. influenzae strains (MIC50 and MIC90 were 0.5 and 1 mg/L, respectively). Thiamphenicol was active against 76.9% of ampicillin-resistant H. influenzae strains (MIC of thiamphenicol < 2 mg/L). The MIC of thiamphenicol was in the range of 0.06–2 mg/L for 96.7% of S. pneumoniae strains (MIC50 and MIC90 were 0.5 and 2 mg/L, respectively). The MIC of thiamphenicol for 90.6% of S. pneumoniae strains with reduced susceptibility to penicillin (MIC of penicillin > 0.06 mg/L) did not exceed 2 mg/L. A total of 88.1% of S. pneumoniae strains resistant to erythromycin were highly susceptible to thiamphenicol (MIC < 2 mg/L). The MIC of thiamphenicol did not exceed 8 mg/L for 96.1% of S. pyogenes strains (MIC50 and MIC90 were 2 and 4 mg/L, respectively). Conclusions. Thiamphenicol was characterized by relatively high in vitro activity, comparable to that of chloramphenicol, against tested strains of H. influenzae, S. pneumoniae and S. pyogenes, including S. pneumoniae isolates with reduced susceptibility to penicillin.

Antimicrobial Activity of Ceftolozane-Tazobactam and Comparators against Clinical Isolates of Haemophilus influenzae from the United States and Europe.

Nine hundred Haemophilus influenzae clinical isolates from 83 U.S. and European medical centers were tested for susceptibility by reference broth microdilution methods against ceftolozane-tazobactam and comparators. Results were stratified by β-lactamase production and infection type. Overall, ceftolozane-tazobactam MIC50/90 values were 0.12/0.25 mg/liter, and 99.0% of isolates were inhibited at the susceptible breakpoint of ≤0.5 mg/liter; the highest MIC value was only 2 mg/liter. Our results support using ceftolozane-tazobactam to treat H. influenzae infections.

In Vitro Investigation of the Antibacterial Activity of Nigella sativa Oil on Some of the Most Commonly Isolated Bacteria in Otitis Media and Externa

This study aimed to evaluate the antibacterial efficacy of Nigella sativa (NS) seed oil against the most frequently isolated infectious bacteria of the middle and external ear. The in vitro antibacterial activity of NS oil was evaluated against 34 clinical isolates of Streptococcus pneumoniae, 32 clinical isolates of Moraxella catarrhalis, 32 clinical isolates of Haemophilus influenzae, and 32 clinical isolates of Pseudomonas aeruginosa. Staphylococcus aureus, Escherichia coli, and P. aeruginosa were also evaluated for their sensitivity to the NS oil. The minimum inhibitory concentration (MIC) of the NS oil was determined via a broth dilution technique. Serial solutions were prepared in a Mueller Hinton-F broth to achieve an ultimate concentration of NS oil within the microplate wells ranging from 256 μg/mL to 0.25 μg/mL. The growth control wells and medium were used for each bacterial strain, and the microplates were incubated at 35°C for 24 h. Those wells having no visible growth and the lowest concentration of NS oil were accepted as showing the MIC. In this study, a comparison was made between NS oil and the various antibiotics known to be effective against the bacterial strains mentioned above. The NS was shown to have bactericidal activity against H. influenzae, M. catarrhalis, and S. pneumoniae. However, the NS was not found to be effective against P. aeruginosa at any concentration. The results of this laboratory-based study support the use of NS oil as an alternative treatment for ear infections. However, it is necessary to conduct clinical studies to evaluate the antibacterial efficacy of NS oil on patients with ear infections.

Molecular diversity of hpd gene in clinical isolates of Haemophilus influenzae

Infections due to Haemophilus influenzae result in tremendous global morbidity. The conjugated vaccines against H. influenzae type b (Hib) have dramatically reduced the incidence of invasive Hib disease in the routine immunization of infants. The several proteins used as vaccine candidates for this pathogen, but they don't produce efficient immune in animal models against all strains of H. influenzae. This study aimed to determine the diversity of hpd gene nucleotide sequences of Iranian native clinical isolates of H. influenzae as a native vaccine candidate compared to standard strains.Twenty isolates of H. influenzae recovered from different clinical specimens of patients admitted to Milad and Imam Khomeini hospitals, Tehran, Iran. Then, isolates detected and identified as H. influenzae using biochemical tests, and further confirmation through omp6 gene PCR. The hpd gene was amplified by PCR using gene-specific primers, and the amplicons digested with EcoR1. For four isolates, the Amplicon of hpd gene sequenced, and the sequences aligned with sequences harbored in GenBank. Subsequently, sequences were submitted to the EMBL site (http://www.ebi.ac.uk/embl/).EcoR1 restriction enzyme pattern was the same among the 19 clinical isolates, and only one isolate was different. That different one with 3 out of 19 isolates were sequenced. The results showed that the nucleotide sequences and the deduced amino acid sequences for protein D in clinical isolates were highly conserved with similarities >95%.In conclusion, regarding high similarity up to 99% in clinical isolates, protein D can be a novel vaccine candidate against all types of H. influenza from Iran. This finding should be proved with more isolates, and also, evaluate the immunological features of protein D in animal models.

Phenotypic detection of clinical isolates of Haemophilus influenzae with altered penicillin-binding protein 3.

The aims of this study were to determine the correlation of mutations in the ftsI gene (coding for PBP3) of Haemophilus influenzae with aminopenicillin resistance and to evaluate the 2017 European Committee for Antibiotic Susceptibility Testing (EUCAST) guidelines for clinical categorization of ampicillin, amoxicillin, and amoxicillin-clavulanate for strains with mutated PBP3 conferring resistance (rPBP3). A panel of 91 H. influenzae isolates was genetically characterized by sequencing of the fstI gene. For all the studied isolates, a screening with benzylpenicillin 1U (BP1) was carried out and minimum inhibitory concentrations (MICs) of ampicillin, amoxicillin, and amoxicillin-clavulanate were tested and interpreted according to EUCAST recommendations. ftsI sequence analysis revealed a total of 14 different amino acid substitutions in PBP3. The substitution patterns most commonly observed were [D350N, M377I, A502V, N526K] among the bla-positive rPBP3 strains (37.5%) and [D350N, A502T, N526K] among the bla-negative rPBP3 strains (24.5%). Screening with BP1 was able to correctly categorize 100% of the bla-negative sPBP3 strains, 100% of the bla-positive strains, and 92% of the bla-negative rPBP3 ones. Only 29% of the bla-negative rPBP3 strains evaluated displayed ampicillin MICs above the current EUCAST resistant breakpoint defined at 1μg/ml. The PBP3 substitution patterns of the strains evaluated are similar to the ones observed in previous Spanish and European studies. Although the screening with BP1 proved to be adequate in the detection of bla-negative rPBP3 strains, these cannot be reliably identified by current 2018 EUCAST breakpoints for ampicillin.

Oldenlandia diffusa Extract Inhibits Biofilm Formation by Haemophilus influenzae Clinical Isolates.

Oldenlandia diffusa has been empirically used as a therapeutic adjunct for the treatment of respiratory infections. To establish the basic evidence of its clinical usefulness, antimicrobial and biofilm inhibitory activities of an O. diffusa extract were examined against clinical isolates of Haemophilus influenzae, a major causative pathogen of respiratory and sensory organ infections. No significant growth inhibitory activity was observed during incubation for more than 6 h after the extract addition into a culture of H. influenzae. On the other hand, biofilm formation by H. influenzae, evaluated by a crystal violet method, was significantly and dose-dependently inhibited by the O. diffusa extract. Furthermore, the mRNA level of the biofilm-associated gene luxS of H. influenzae significantly decreased soon after the extract addition, and the suppressive effect continued for at least 2 h. At 2 h after the addition of the O. diffusa extract, the autoinducer in the culture supernatant was also significantly reduced by the O. diffusa extract in a dose-dependent manner. These results revealed that O. diffusa extract shows inhibitory activity against luxS-dependent biofilm formation but has no antimicrobial activity against planktonic cells of H. influenzae. Thus, O. diffusa extract might be useful as an adjunctive therapy for the treatment of respiratory infections caused by H. influenzae.

Acquired macrolide resistance genes in Haemophilus influenzae?

The objective of this study was to determine the prevalence of specific acquired macrolide resistance genes previously reported as present in clinical isolates of Haemophilus influenzae. A collection of 172 clinical respiratory isolates of H. influenzae, including 59 isolates from cystic fibrosis patients and 27 from non-cystic fibrosis bronchiectasis patients with significant prior macrolide use, was established. This collection was tested for azithromycin susceptibility using Etest and screened for the presence of erm(A), erm(B), erm(C), erm(F), mef(A) and mef(E) using locked nucleic acid dual-labelled hydrolysis probes. The azithromycin MICs ranged from 0.09 to >256 mg/L, with 2 (1.2%) isolates susceptible, 163 (94.8%) intermediate and 7 (4%) resistant according to EUCAST breakpoints (susceptible, ≤0.12 mg/L; resistant, >4 mg/L). None of the acquired macrolide resistance genes erm(A), erm(B), erm(C), erm(F), mef(A) or mef(E) was detected in any of the isolates. The specific acquired macrolide resistance genes are not widespread in H. influenzae and the high prevalence of these genes previously reported might be unique to the specific circumstances of that study.

Comparative Analysis of the Antibacterial Activity of a Novel Peptide Deformylase Inhibitor, GSK1322322

GSK1322322 is a novel peptide deformylase (PDF) inhibitor being developed for the intravenous and oral treatment of acute bacterial skin and skin structure infections and hospitalized patients with community-acquired pneumonia. The activity of GSK1322322 was tested against a global collection of clinical isolates of Haemophilus influenzae (n = 2,370), Moraxella catarrhalis (n = 115), Streptococcus pneumoniae (n = 947), Streptococcus pyogenes (n = 617), and Staphylococcus aureus (n = 940), including strains resistant to one or more marketed antibiotics. GSK1322322 had an MIC(90) of 1 μg/ml against M. catarrhalis and 4 μg/ml against H. influenzae, with 88.8% of β-lactamase-positive strains showing growth inhibition at that concentration. All S. pneumoniae strains were inhibited by ≤ 4 μg/ml of GSK1322322, with an MIC(90) of 2 μg/ml. Pre-existing resistance mechanisms did not affect its potency, as evidenced by the MIC(90) of 1 μg/ml for penicillin, levofloxacin, and macrolide-resistant S. pneumoniae. GSK1322322 was very potent against S. pyogenes strains, with an MIC(90) of 0.5 μg/ml, irrespective of their macrolide resistance phenotype. This PDF inhibitor was also active against S. aureus strains regardless of their susceptibility to methicillin, macrolides, or levofloxacin, with an MIC(90) of 4 μg/ml in all cases. Time-kill studies showed that GSK1322322 had bactericidal activity against S. pneumoniae, H. influenzae, S. pyogenes, and S. aureus, demonstrating a ≥ 3-log(10) decrease in the number of CFU/ml at 4× MIC within 24 h in 29 of the 33 strains tested. Given the antibacterial potency demonstrated against this panel of organisms, GSK1322322 represents a valuable alternative therapy for the treatment of infectious diseases caused by drug-resistant pathogens.

Antimicrobial Resistance Genotype Trend and Its Association with Host Clinical Characteristics in Respiratory Isolates of Haemophilus influenzae

Background: β-Lactam resistance genotype trends in clinical isolates of Haemophilus influenzae and their correlation with the clinical background were analyzed. Methods: Five hundred and ten respiratory isolates of H. influenzae collected during the period 2002–2009 were classified by PCR into gBLNAS (genotype for β-lactamase-negative ampicillin-susceptible), gBLNAR (genotype for β-lactamase-negative ampicillin-resistant) and 3 other genotypes. The associations with host clinical data and antimicrobial susceptibility were analyzed in all 144 isolates between 2008 and 2009. Results: The 8-year trend analysis detected an increase in gBLNAR with a decrease in gBLNAS. The probability of being a causative pathogen did not differ between genotypes. Host clinical characteristics such as age and gender did not differ with gBLNAR or gBLNAS, but the underlying respiratory diseases did differ. gBLNAR was found at the highest rate in 83% of isolates from patients with nontuberculous mycobacteriosis. In contrast, gBLNAR accounted for as little as 33% of isolates from chronic obstructive pulmonary disease. Conclusions: There were no differences in the pathogenicity of gBLNAR and gBLNAS. The underlying respiratory diseases may be related to the resistance genotype.

Polymorphism in ftsI gene and -lactam susceptibility in Portuguese Haemophilus influenzae strains: clonal dissemination of -lactamase-positive isolates with decreased susceptibility to amoxicillin/clavulanic acid

The aim of this study was to characterize ampicillin resistance mechanisms in clinical isolates of Haemophilus influenzae from Portugal. Association between specific patterns of amino acid substitutions in penicillin-binding protein 3 (PBP3) (with or without β-lactamase production) and β-lactam susceptibility as well as genetic relatedness among isolates were investigated. Two-hundred and forty non-consecutive H. influenzae isolates chosen according to their different ampicillin MICs [101 β-lactamase-non-producing ampicillin-resistant (BLNAR) isolates, 80 β-lactamase-producing ampicillin-resistant (BLPAR) isolates and 59 β-lactamase-non-producing ampicillin-susceptible (BLNAS) isolates] were analysed. The β-lactamase-encoding bla(TEM-1) gene was detected by PCR. The ftsI gene encoding PBP3 was sequenced. Genetic relatedness among isolates was examined by PFGE. Of the 240 H. influenzae isolates, 141 had mutations in the transpeptidase domain of the ftsI gene, including most BLNAR strains (94/101, 93.1%) and a high percentage of BLPAR strains (47/80, 58.8%). As previously reported, the latter have been described as β-lactamase-positive amoxicillin/clavulanic acid resistant (BLPACR). The most common amino acid substitutions were identified near the KTG motif: N526K (136/141, 96.5%), V547I (124/141, 87.9%) and N569S (121/141, 85.8%). The 141 strains were divided into 31 ftsI mutation patterns and included six groups (I, IIa, IIb, IIc, IId and III-like). BLNAR strains were genetically diverse but close genetic relationships were demonstrated among BLPACR strains. This study shows that the non-enzymatic mechanism of resistance to β-lactams is widespread among H. influenzae isolates in Portugal. Clonal dissemination of BLPACR strains showing high resistance to ampicillin and reduced susceptibility to amoxicillin/clavulanic acid was documented.

2004 年から2008 年の小児由来<i>Haemophilus influenzae </i>の抗菌薬感受性に関する検討

We tested for antimicrobial susceptibility of 1,317 clinical isolates of Haemophilus influenzae at a pediatric facility during 2004-2008. The percentage distribution of beta-lactamase-non-producing ampicillin (ABPC)-sensitive strain (BLNAS) was 47.8%, that of beta-lactamase-non-producing ABPC-resistant strain (BLNAR) 32.7% that of intermediately resistant strain (BLNAI) 8.9% that of beta-lactamase producing ABPC resistant strain (BLPAR) 6.8% and that of clavulanic acid/amoxicillin resistant strain (BLPACR) 3.7%. BLNAR prevalence was 30% between 2005 and 2008, increasing slowly. Though reduced susceptibility was seen in most beta-lactams, piperacillin and tazobactam/piperacillin showed good susceptibility for H. influenzae. Of 1,317 strains, 83 (6.3%) were serotype b (Hib). The frequency of Hib was high in sterilized site.

Antibiotic Resistance in Haemophilus influenzae Decreased, except for β-Lactamase-Negative Amoxicillin-Resistant Isolates, in Parallel with Community Antibiotic Consumption in Spain from 1997 to 2007

The susceptibility to 14 antimicrobial agents and the mechanisms of aminopenicillin resistance were studied in 197 clinical isolates of Haemophilus influenzae--109 isolated in 2007 (study group) and 88 isolated in 1997 (control group). Community antibiotic consumption trends were also examined. H. influenzae strains were consecutively isolated from the same geographic area, mostly from respiratory specimens from children and adults. Overall, amoxicillin resistance decreased by 8.4% (from 38.6 to 30.2%). Beta-lactamase production decreased by 15.6% (from 33 to 17.4%, P = 0.01), but amoxicillin resistance without beta-lactamase production increased by 7.1% (from 5.7 to 12.8%). All beta-lactamase-positive isolates were TEM-1, but five different promoter regions were identified, with Pdel being the most prevalent in both years, and Prpt being associated with the highest amoxicillin resistance. A new promoter consisting of a double repeat of 54 bp was detected. Community consumption of most antibiotics decreased, as did the geometric means of their MICs, but amoxicillin-clavulanic acid and azithromycin consumption increased by ca. 60%. For amoxicillin-clavulanic acid, a 14.2% increase in the population with an MIC of 2 to 4 microg/ml (P = 0.02) was observed; for azithromycin, a 21.2% increase in the population with an MIC of 2 to 8 microg/ml (P = 0.0005) was observed. In both periods, the most common gBLNAR (i.e., H. influenzae isolates with mutations in the ftsI gene as previously defined) patterns were IIc and IIb. Community consumption of trimethoprim-sulfamethoxazole decreased by 54%, while resistance decreased from 50 to 34.9% (P = 0.04). Antibiotic resistance in H. influenzae decreased in Spain from 1997 to 2007, but surveillance should be maintained since new forms of resistances may be developing.

Population distributions of minimum inhibitory concentration - increasing accuracy and utility

To generate continuous minimum inhibitory concentration (MIC) data that describes the discrete nature of experimentally derived population MIC data. A logistic model was fitted to experimentally derived MIC population cumulative distributions from clinical isolates of Haemophilus influenzae, Moraxella catarrhalis, Streptococcus pneumoniae and Staphylococcus aureus (European Committee on Antimicrobial Susceptibility Testing, BSAC and MYSTIC population susceptibility databases). From the model continuous distributions of population susceptibility were generated. The experimentally observed population distributions based on discrete MIC could be reproduced from this underlying continuous distribution. Monte Carlo (MC) simulation was used to confirm findings. Where the discrete experimental data contained few or no isolates with MIC greater or less than the antimicrobial concentration range tested, the true mean MIC was a factor of 0.707 times that normally reported and may be of little clinical significance. Where data contained isolates beyond the range of concentration used, the true MIC was dependent on the SD and the number of isolates and could be clinically significant. Subpopulations of differing susceptibilities could be modelled successfully using a modified logistic equation: this allows a more accurate examination of the data from these databases. The mean MIC and SD of population data currently reported are incorrect as the method of obtaining such parameters relies on normally distributed data which current MIC population data are not. Obtaining the distribution parameters from the underlying continuous distribution of MIC can be carried out using a simple logistic equation. MC simulation using these values allows easy visualization of the discrete data. The analyses of subpopulations within the data should increase the usefulness of horizontal studies.

Codon usage comparison of novel genes in clinical isolates of Haemophilus influenzae

A similarity statistic for codon usage was developed and used to compare novel gene sequences found in clinical isolates of Haemophilus influenzae with a reference set of 80 prokaryotic, eukaryotic and viral genomes. These analyses were performed to obtain an indication as to whether individual genes were Haemophilus-like in nature, or if they probably had more recently entered the H.influenzae gene pool via horizontal gene transfer from other species. The average and SD values were calculated for the similarity statistics from a study of the set of all genes in the H.influenzae Rd reference genome that encoded proteins of 100 amino acids or longer. Approximately 80% of Rd genes gave a statistic indicating that they were most like other Rd genes. Genes displaying codon usage statistics >1 SD above this range were either considered part of the highly expressed group of H.influenzae genes, or were considered of foreign origin. An alternative determinant for identifying genes of foreign origin was when the similarity statistics produced a value that was much closer to a non-H.influenzae reference organism than to any of the Haemophilus species contained in the reference set. Approximately 65% of the novel sequences identified in the H.influenzae clinical isolates displayed codon usages most similar to Haemophilus sp. The remaining novel sequences produced similarity statistics closer to one of the other reference genomes thereby suggesting that these sequences may have entered the H.influenzae gene pool more recently via horizontal transfer.

In vitro Antibacterial Activities of New Fluoroquinolones against Clinical Isolates of Haemophilus influenzae with Ciprofloxacin-Resistance-Associated Alterations in GyrA and ParC

Background: The in vitro antimicrobial activities of new fluoroquinolones were tested against quinolone-resistant Haemophilus influenzae of clinical isolates. Methods: The nucleotide sequences of the gyrA and parC genes from three ciprofloxacin-resistant strains of Haemophilus influenzae (MIC, 1.56–6.25 µg/ml) were determined. The gyrase was purified from the clinical isolates, and the inhibitory activities of quinolones against the enzyme were tested. Results: These strains possessed at least one amino acid substitution in each of the GyrA (asparagine at residue 88 (Asp-88) to Tyr, Ser-84 to Leu or Ser-84 to Leu and Asp-88 to Asn) and ParC (Glu-88 to Lys). The antibacterial activity of olamufloxacin against the resistant strains was most potent compared with other quinolones, and the inhibitory activities correlated with quinolone resistance of these strains. Conclusions: These results warrant the clinical effects of new types of fluoroquinolones, such as olamufloxacin, against respiratory tract and otolaryngology infections caused by ciprofloxacin-resistant H. influenzae.

Antimicrobial resistance among clinical isolates of haemophilus influenzae in the United States

Study objectives: Increasing rates of β-lactamase production and antimicrobial resistance by respiratory tract pathogens continue to be a concern in the treatment of a variety of infections commonly cared for in the emergency department setting. We determine the current antimicrobial susceptibility patterns and β-lactamase production rates of <i>Haemophilus influenzae</i> and compare them with our results from the previous 6 years. Methods: A total of 5,445 isolates were collected from patients with <i>H influenzae</i> respiratory tract infections between 1994 and 2002. The most recent study was completed using specimens collected during the winter of 2001 to 2002 and included 1,025 strains. β-Lactamase production was assessed with the nitrocefin disc assay; broth microdilution antimicrobial susceptibility testing with 16 antimicrobial agents was performed according to National Committee for Clinical Laboratory Standards guidelines. Results: The rate of β-lactamase production was 36.4% in 1994 and decreased in each of the subsequent study periods (1997, 31%; 1999, 30.8%; and 28.9% in 2001 to 2002). Susceptibility rates of greater than 96% were found with amoxicillin/clavularic acid, cefuroxime, cefpodoxime, cefixime, ciprofloxacin, azithromycin, chloramphenicol, tetracycline, and telithromycin. Susceptibility rates to ampicillin (67.5%), cefprozil (88.1%), and cefaclor (87.3%) were unchanged during the study period. Only trimethoprim/sulfamethoxazole (74.5% versus 100% in 1994) and clarithromycin (60.5% versus 71.2 in 1994) revealed a decreasing rate of susceptibility between 1994 and 2002. Conclusion: Since 1994 to 1995, β-lactamase production has decreased and trimethoprim/sulfamethoxazole and clarithromycin resistance has increased in clinical isolates of <i>H influenzae.</i> The reasons for these trends were not determined but may be a result of a change in clinician prescribing practices away from β-lactam drugs.

Antimicrobial susceptibility of 840 clinical isolates of Haemophilus influenzae collected in four European countries in 2000-2001

In 2000-2001, 840 clinical isolates of Haemophilus influenzae were collected from laboratories in France, Germany, Italy and Spain (210 isolates/country). Beta-Lactamase production among the isolates varied considerably by country, ranging from 8.1% in Germany to 34.8% in France. H. influenzae from patients <or=4 years old showed the highest prevalence of beta-lactamase production (23.2%), compared with isolates from patients aged 5-17 years (17.8%) and >or=18 years (16.5%). All isolates were susceptible to amoxicillin-clavulanate, ciprofloxacin and levofloxacin; 99.6% and 98.9% of isolates were susceptible to azithromycin and cefuroxime, respectively. Among the macrolides tested, azithromycin (MIC90, 2 mg/L) was eight-fold more potent than clarithromycin (MIC90, 16 mg/L) and roxithromycin (MIC90, 16 mg/L). Despite variations in beta-lactamase production between different countries, > 99% of all isolates were susceptible to amoxicillin-clavulanate, ciprofloxacin, levofloxacin, and azithromycin.

Evaluation of the WIDER I system for antimicrobial susceptibility testing of clinical isolates of Haemophilus influenzae and Streptococcus pneumoniae

The aim of this study was to evaluate the WIDER I system for susceptibility testing of Haemophilus influenzae and Streptococcus pneumoniae. MICs of 12 antimicrobials against 42 H. influenzae and 58 S. pneumoniae strains were determined using 1W MIC panels and compared with those obtained by microdilution. Overall essential agreements were >99%. Very major errors were not detected. Major errors occurred with ampicillin (1.7% H. influenzae). Minor errors were 2.3% (amoxicillin-clavulanate, cefuroxime, chloramphenicol), 7.1% (ampicillin) and 16.7% (clarithromycin) for H. influenzae, and 1.7% (chloramphenicol, erythromycin, meropenem), 3.4% (amoxicillin-clavulanate, cefuroxime, tetracycline) and 8.6% (levofloxacin) for S. pneumoniae. The WIDER I system is a reliable method for susceptibility testing of H. influenzae and S. pneumoniae.

Apparent plateau in β-lactamase production among clinical isolates of Haemophilus influenzae and Moraxella catarrhalis in the United States: results from the LIBRA Surveillance initiative

Haemophilus influenzae ( n=2791) and Moraxella catarrhalis ( n=1249) isolated from patient specimens during 1999 were collected from 290 laboratories participating in a moxifloxacin surveillance study as part of the LIBRA Surveillance intitiative. Isolates were tested for in vitro susceptibility to a panel of agents suitable for the treatment of respiratory tract infections. β-Lactamase production was identified in 32.2% of H. influenzae and 94.2% of M. catarrhalis. These percentages differed by less than 1.5% from results of a study conducted in 1997–1998 and were similar to results from other recent US surveillance studies. Resistance among H. influenzae to trimethoprim-sulphamethoxazole increased considerably, from 2% in the 1997–1998 study ( n=6588 H. influenzae) to 15.5% in the current study. One isolate of H. influenzae had an MIC of 8 mg/l to both levofloxacin and moxifloxacin; all other isolates had MICs of ≤0.5 mg/l and ≤0.25 mg/l, respectively. β-Lactamase production was found to confer ampicillin resistance in nearly all isolates. For M. catarrhalis, β-lactamase-negative isolates had MICs ≤0.12–0.25 mg/l for ampicillin and ≤0.03–0.12 mg/l for ceftriaxone. In contrast, β-lactamase production resulted in MICs of ≤0.12–>16 mg/l for ampicillin and ≤0.03–4 mg/l for ceftriaxone. All M. catarrhalis had MICs ≤0.12 mg/l for moxifloxacin and ≤1 mg/l for levofloxacin. In summary, antimicrobial susceptibilities and the prevalence of β-lactamase production in H. influenzae and M. catarrhalis in the United States has remained essentially unchanged from 1997–1998 to 1999.