You are here: Home Research Themes Antimicrobial Therapy

Antimicrobial Therapy

Article Reference S-carboxymethylcysteine inhibits the attachment of Streptococcus pneumoniae to human pharyngeal epithelial cells.
Streptococcus pneumoniae causes respiratory and other invasive infections. Increased resistance of this bacterium to antibiotics necessitates new approaches to the treatment of infections. Attachment of bacteria to human pharyngeal epithelial cells is the initial step in the pathogenesis of infection and S-carboxymethylcysteine (S-CMC) can modulate the attachment of Moraxella catarrhalis and nontypable Haemophilus influenzae to epithelial cells. Unlike these two, S. pneumoniae is gram-positive and has a well-defined capsule. Here we examined the effects of S-CMC on the attachment and detachment of S. pneumoniae to human pharyngeal epithelial cells in vitro. Treatment of these cells with S-CMC significantly reduced the number of attached S. pneumoniae. S-CMC also resulted in a significant increase in the detachment of already attached S. pneumoniae to epithelial cells. In addition, treatment of S. pneumoniae with S-CMC significantly reduced their ability to attach to epithelial cells, but not the number of viable bacteria. Our study shows that S-CMC modulates the attachment of S. pneumoniae to human pharyngeal epithelial cells by acting both on cells and bacteria.
Article Reference Respiratory infections caused by non-typeable Haemophilus influenzae.
This review will consider recent developments in the clinical aspects of infections due to non-typeable Haemophilus influenzae. In addition, newer developments in the areas of mechanisms of pathogenesis, host pathogen interaction, immune responses and efforts toward vaccine development will be reviewed briefly.
Article Reference Comparison of the antibacterial activities of ampicillin, ciprofloxacin, clarithromycin, telithromycin and quinupristin/dalfopristin against intracellular non-typeable Haemophilus influenzae.
Non-typeable Haemophilus influenzae, which is a cause of disease in the upper and lower respiratory tract, can survive intracellularly in human epithelial cells and macrophages. We studied the in vitro activity of five antibiotics against intracellular non-typeable H. influenzae in human type II alveolar epithelial cells. The eukaryotic cells were loaded with bacteria, and extracellular bacteria were killed by gentamicin. After the cells were washed, antibiotics were added at concentrations of 0.12-64 mg/L for 18 h before the numbers of viable intracellular bacteria were determined. Of the antibiotics tested, ciprofloxacin and quinupristin/dalfopristin were the most potent agents, followed by clarithromycin and telithromycin. Ampicillin was not active against intracellularly localized, non-typeable H. influenzae.
Article Reference Chronic obstructive pulmonary disease: role of bacteria and guide to antibacterial selection in the older patient.
Chronic obstructive pulmonary disease (COPD) is a common problem in the elderly. The disease is characterised by intermittent worsening of symptoms and these episodes are called acute exacerbations. The best estimate, based on several lines of evidence, is that approximately half of all exacerbations are caused by bacteria. These lines of evidence include studies of lower respiratory tract bacteriology during exacerbations, correlation of airways' inflammation with results of sputum cultures during exacerbations, analysis of immune responses to bacterial pathogens, and the observation in randomised, prospective, placebo-controlled trials that antibacterial therapy is of benefit. The most important bacterial causes of exacerbations of COPD are nontypeable Haemophilus influenzae, Moraxella catarrhalis, Streptococcus pneumoniae and Chlamydia pneumoniae. In approaching the elderly patient with an exacerbation, it is useful to consider the severity of the exacerbation based on three cardinal symptoms: increased sputum volume, increased sputum purulence and increased dyspnoea compared with baseline. Patients experiencing moderate (two symptoms) or severe (all three symptoms) exacerbations benefit from antibacterial therapy. Consideration of underlying host factors allows for a rational choice of antibacterial agent. Patients are considered to have 'simple COPD' or 'complicated COPD' based on: (i) the severity of underlying lung disease; (ii) the frequency of exacerbations; and (iii) the presence of comorbid conditions. It is proposed that patients with simple COPD are treated with doxycycline, a newer macrolide, or an extended-spectrum oral cephalosporin; and patients with complicated COPD are treated with amoxicillin/clavulanate or a fluoroquinolone. The major goals of antibacterial therapy for exacerbations of COPD are acceleration of symptom resolution and prevention of the complications of exacerbation.
Article Reference Susceptibility of nontypeable Haemophilus influenzae to human beta-defensins is influenced by lipooligosaccharide acylation.
Nontypeable Haemophilus influenzae (NTHI) lipooligosaccharide htrB mutants exhibited greater than 45-fold-increased sensitivity to human beta-defensin 2 (HBD-2) compared to the wild type. Complementation by htrB in trans to acylation competence reversed this increased sensitivity. In contrast, NTHI was more susceptible to HBD-3 and showed no changes in sensitivity as a result of lipooligosaccharide mutations in oligosaccharide and lipid A biosynthesis genes.
Article Reference Antibiotics in the treatment of acute exacerbations of chronic bronchitis.
The benefit of antimicrobial therapy for patients with an acute exacerbation of chronic bronchitis (AECB) remains controversial for two main reasons. First, the distal airways of patients with chronic bronchitis are persistently colonised, even during clinically stable periods, with the same bacteria that have been associated with AECB. Second, bacterial infection is only one of several causes of AECB. These factors have led to conflicting analyses on the role of bacterial agents and the response to antimicrobial therapy of patients with AECB. An episode of AECB is said to be present when a patient with chronic obstructive pulmonary disease (COPD) experiences some combination of increased dyspnoea, increased sputum volume, increased sputum purulence and worsening lung function. While the average COPD patient experiences 2 - 4 episodes of AECB per year, some patients, particularly those with more severe airway obstruction, are more susceptible to these attacks than others. Bacterial agents appear to be particularly associated with AECB in patients with low lung function and those with frequent episodes accompanied by purulent sputum. Non-typeable Haemophilus influenzae, Streptococcus pneumoniae and Moraxella catarrhalis account for up to 50% of episodes of AECB. Gram-negative bacilli are more likely to occur in patients with more severe lung disease. Antibiotics have been used to ameliorate AECB, to prevent AECB and to prevent the long-term loss of lung function that characterises COPD. Numerous prevention trials have been conducted with fairly consistent results; antibiotics do not lessen the number of episodes of AECB but do reduce the number of days lost from work. Most antibiotic trials have studied the impact of treatment on episodes of AECB and results have been inconsistent, largely due to patient selection and end point definition. In patients with severe airway obstruction, especially in the presence of purulent sputum, antibiotic therapy significantly shortens the duration of symptoms and can be cost-effective. Over the past 50 years, virtually all classes of antimicrobial agents have been studied in AECB. Important considerations include penetration into respiratory secretions, spectrum of activity and antimicrobial resistance. These factors limit the usefulness of drugs such as amoxicillin, erythromycin and trimethoprim-sulfamethoxazole. Extended-spectrum oral cephalosporins, newer macrolides and doxycycline have demonstrated efficacy in clinical trials. Amoxicillin-clavulanate and flouoroquinolones should generally be reserved for patients with more severe disease. A number of investigational agents, including ketolides and newer quinolones, hold promise for treatment of AECB.
Article Reference Impact of IgG replacement therapy and antibiotic treatment on the colonization of non-encapsulated Haemophilus influenzae in the nasopharynx in patients with hypogammaglobulinaemia.
Non-typable Haemophilus influenzae (NTHI) and Streptococcus pneumoniae are regarded as the main pathogens in patients with humoral immunodeficiency. These patients have been given IgG replacement therapy since the 1950s. However, a number of individuals still suffer from recurrent episodes of respiratory tract infections. Nasopharyngeal cultures were obtained on a regular basis over a 3-6-month period from 11 patients with common variable immunodeficiency disease in 1989 and 1998. The proportion of cultures positive for NTHI decreased from 56% in 1989-90 to 16% in 1998-99 (p < 0.003). After 9 y of IgG therapy, 7 of the 11 patients were free from NTHI in the nasopharynx. Specific NTHI strains were analysed by pulsed-field gel electrophoresis and compared, with regard to genetic relatedness, on an intra-individual basis. In 1 patient the same NTHI strain was found in both 1989 and 1999. The apparent absence of NTHI from the nasopharynx in most of the patients was assumed to be due to subcutaneous IgG treatment, as well as adequate antibiotic treatment.
Article Reference [Study on serotyping of Haemophilus influenzae and the positive rates of beta-lactamase].
To investigate the serotypes of both infectious and carriage strains of Haemophilus influenzae (Hi) and to evaluate the prevalence of beta-lactamase of major serotypes in Shanghai.
Article Reference The role of antibacterial therapy of acute otitis media in promoting drug resistance.
Treatment of acute otitis media (AOM) is the leading cause of antibacterial use in children in most developed countries. Rates of Streptococcus pneumoniae strains resistant to many classes of antibacterial agents have risen dramatically in many countries over the past 20 years. While more restricted use of antibacterial agents for AOM would almost certainly slow the rise in resistance, AOM is a potentially painful disease and may have suppurative complications such as mastoiditis. In this review, we discuss the prudent use of antibacterial agents for AOM and provide an overview of the epidemiology of S. pneumoniae resistance worldwide. Data from 10 placebo-controlled studies in patients with AOM show that antibacterial treatment is generally associated with a significantly higher cure rate than placebo. Of the three studies which analysed children <2 years of age, cure rates were 28 to 48% for placebo and 41 to 74% with antibacterial agents. Of the studies purporting to show no difference in cure rates between placebo and antibacterial therapy, the diagnostic criteria defining entry into the study were poor; therefore, the studies may have included many children without bacterial disease. Accurate diagnosis of AOM is the key element in reducing unnecessary antibacterial usage. Either pneumatic otoscopy or tympanometry can provide evidence of an effusion and the presence of an opaque, yellow or creamy white bulging eardrum will confirm AOM. Finally, the selection of appropriate antibacterial agents will reduce the rise in resistance. Low dosages of antibacterial agents used for prophylaxis select for resistance, and certain classes of drugs such as the sulfonamides and macrolides appear to do the same even at therapeutic doses. Amoxicillin at high dosages should remain the first-line antibacterial agent. In the future, use of vaccination strategies against pneumococci, influenza, respiratory syncytial virus and non-typeable Haemophilus influenzae will also decrease antibacterial use.
Article Reference Clinical significance of resistant organisms in otitis media.
Otitis media is an important health care problem of childhood. The bacteriology of otitis media comprises three main pathogens: Streptococcus pneumoniae, nontypable Haemophilus influenzae and Moraxella catarrhalis. Although the prevalence of resistant strains varies geographically and temporally, antimicrobial resistance is widespread and increasing.
Article Reference Efficacy of linezolid in experimental otitis media.
Therapy for otitis media (OM) due to resistant Streptococcus pneumoniae (MIC of penicillin, >/=2.0 microgram/ml) is challenging. Linezolid, an oxazolidinone, represent a new class of antimicrobial agents with excellent in vitro activity against penicillin-resistant S. pneumoniae; however, in vitro activity against nontypeable Haemophilus influenzae (NTHI) is limited. We evaluated its efficacy against experimental acute OM due to a multidrug-resistant S. pneumoniae isolate and two isolates of NTHI. The chinchilla model was utilized to evaluate the efficacy of linezolid against experimental infection due to S. pneumoniae or NTHI. Serum and middle ear antibiotic concentrations were determined, and sterilization of experimental OM was evaluated. Chinchillas were inoculated directly with S. pneumoniae into the superior bulla. Twenty-four hours after inoculation, all animals had positive middle ear and nasopharyngeal cultures. Animals were given linezolid at 25 mg/kg/dose twice a day (b.i.d.) by orogastric feeding tube or amoxicillin at 40 mg/kg/dose b.i.d. intramuscularly for 5 days. By day 5, all animals in the linezolid group had sterile middle ear cultures and eradication of S. pneumoniae from the nasopharynx. In the amoxicillin group, all nine animals remained middle ear and nasopharynx positive (P < 0.01). In animals inoculated with NTHI, 25 and 37.5 mg/kg b.i.d. failed to sterilize middle ear infection or eradicate colonization. Mean levels in middle ear fluid measured during experimental infection were 12.8 microgram/ml at 2 to 6 h and 4. 1 mirogram/ml at 16 to 17 h after orogastric dosing at 25 mg/kg. Linezolid achieved a high concentration in the middle ear during experimental OM. Linezolid eradicated multidrug-resistant S. pneumoniae from the middle ear and nasopharynx. Experimental infection and nasopharyngeal colonization due to NTHI persisted despite achievement of concentrations in the middle ear that were above the MIC (for NTHI).
Article Reference Effects of clarithromycin on cultured human nasal epithelial cells and fibroblasts.
Long-term administration of clarithromycin has been reported to be effective in the treatment of chronic sinusitis. To investigate the mechanism underlying the anti-inflammatory activity of clarithromycin, the authors evaluated the effect of clarithromycin on the gene expression of proinflammatory cytokine and the DNA-binding activity of nuclear factor (NF)-kappa B in cultured human nasal epithelial cells and fibroblasts. Cells were incubated with endotoxin purified from nontypable Haemophilus influenzae or interleukin (IL)-1 beta in the presence of clarithromycin.
Article Reference Simultaneous respiratory tract colonization by multiple strains of nontypeable haemophilus influenzae in chronic obstructive pulmonary disease: implications for antibiotic therapy.
Nontypeable Haemophilus influenzae often causes exacerbations of chronic obstructive pulmonary disease (COPD), and these exacerbations are frequently treated with oral antibiotics. The goals of this study were to determine the frequency of the simultaneous presence of multiple strains of H. influenzae in sputum and to measure the MICs of antibiotics for the isolates. In a prospective study, adults with COPD were seen monthly. Sputum cultures were obtained, and individual colonies were subjected to genomic DNA typing and MIC determinations. Multiple strains of H. influenzae were present simultaneously in the sputum of 26.3% of adults with COPD. In 64.5% of these, MICs of >/=1 antibiotic varied by >/=4-fold among the strains. Therefore, multiple strains of H. influenzae are frequently present simultaneously in the sputum of adults with COPD, and the antimicrobial susceptibility of different strains in the same sputum sometimes differs.
Article Reference Susceptibility and genetic relatedness of invasive Haemophilus influenzae type b in Italy.
Haemophilus influenzae type b (Hib) still causes a large portion of meningitis in children less than 5 year old in Italy because vaccination against this agent has not been fully implemented in the country. We have studied 78 Hib strains and 4 nontypable H. influenzae (NTHi) isolated from the cerebrospinal fluid of subjects with meningitis for susceptibility to ampicillin, chloramphenicol, and ceftriaxone. The macrorestriction profiles of chromosomal DNA obtained by pulsed-field gel electrophoresis (PFGE) following digestion with SmaI and ApaI were also determined. All strains except one were equally susceptible to the antibiotics tested. One Hib strain, the only beta-lactamase producer, showed an intermediate susceptibility to ampicillin (MIC = 2 microg/ml), while maintaining full susceptibility to chloramphenicol and ceftriaxone. The analysis of the PFGE patterns showed that most of the Hib isolates, including the beta-lactamase-positive Hib strain, belonged to the same clone or to closely related subclones. For three PCR-confirmed NTHi isolates, we obtained completely different PFGE profiles. In conclusion, resistance to ampicillin still appears to be a rare finding in Hib strains causing meningitis in Italy; moreover, PFGE showed that the population structure of invasive Hib is essentially clonal.
Article Reference The role of infection in COPD.
Clinical studies of acute exacerbations of COPD are difficult because of the heterogeneous nature of COPD, diffuse symptoms that can vary spontaneously, and difficulties in defining clinical response both in the short and long term. The role of bacterial infection, and thus use of antibiotics, in COPD is controversial. The available evidence shows that bacterial infection has a significant role in acute exacerbations, but its role in disease progression is less certain. Upper respiratory tract commensals, such as nontypable Haemophilus influenzae, cause most bronchial infections by exploiting deficiencies in the host defenses. Some COPD patients are chronically colonized by bacteria between exacerbations, which represents an equilibrium in which the numbers of bacteria are contained by the host defenses but not eliminated. When an exacerbation occurs, this equilibrium is upset and bacterial numbers increase, which incites an inflammatory response. Neutrophil products can further impair the mucosal defenses, favoring the bacteria, but if the infection is overcome, symptoms resolve. However, if the infection persists, chronic inflammation may cause lung damage. About half of exacerbations involve bacterial infection, but these patients are not easy to differentiate from those who are uninfected, which means that antibiotics have to be given more often than is strictly necessary. Further research is needed to characterize those patients in whom bacterial infection has a more important role.
Article Reference The effect of antibiotic treatment on the release of endotoxin during nontypable Haemophilus influenzae-induced otitis media in the chinchilla.
The gram negative bacteria, nontypable Haemophilus influenzae (NTHi) was used to induce otitis media in a total of 18 chinchillas. Three days post-inoculation, three cohorts of 6 chinchillas each were treated daily for four days with either ceftriaxone, chloramphenicol, or diluent without antibiotics. Middle ear fluid (MEF) was obtained daily, assayed for endotoxin content by means of the chromogenic limulus amebocyte lysate assay, and concentration of the NTHi/mL MEF determined by standard plate count. The endotoxin concentration per mL MEF from both the antibiotic treated cohorts decreased during the observation period, but increased in the MEF of the untreated control group. The data indicate that, unlike the dramatic increase in endotoxin concentration, after antibiotic treatment in the cerebrospinal fluid (CSF) during experimental Haemophilus influenzae-induced meningitis, there is no demonstrable sustained release of endotoxin in the middle ear subsequent to antibiotic treatment during experimental otitis media.
Article Reference New murine model of bronchopneumonia due to cell-bound Haemophilus influenzae.
This murine model of nontypeable (unencapsulated) Haemophilus influenzae (NTHI) bronchopneumonia used organisms bound to mouse fetal lung (MFL) cells as an inoculum. Pretreatment of the mice with 40 microL of 1% formalin 3 days before intranasal instillation of the bacteria was necessary to allow infection. The number of NTHI recovered from the lungs plus trachea on day 7 after instillation was >100 times the number originally inoculated. Later, however, the number of recovered bacteria diminished gradually, and by day 14 it was almost identical to the original inoculum size. Serum IgM also peaked on day 7 after infection, after which IgG increased while IgM decreased. Histologically, bronchoalveolar infiltration of neutrophils was observed on day 3 after inoculation and continued at least for the following 4 days. The present experiment demonstrates that MFL cells can protect bacteria that have invaded the cells from the opsonizing and killing activities of host humoral defense mechanisms.
Article Reference Nontypeable Haemophilus influenzae susceptibility: effect of inoculum size and beta-lactamase production.
The activities of cefixime, cefpodoxime, cefprozil, cefuroxime, loracarbef, and amoxicillin/clavulanate against 72 clinical isolates of nontypeable Haemophilus influenzae were determined by using an agar dilution method. The effects of beta-lactamase production and bacterial inoculum size were investigated. All antimicrobials exhibited a significant inoculum effect, demonstrating the importance of accurately determining inoculum size in the performance of antimicrobial susceptibility testing of H. influenzae.
Article Reference The effects of low concentrations of antibiotics on epithelial damage caused by non-typable Haemophilus influenzae and bacterial morphology.
Sterile culture filtrates from non-typable Haemophilus influenzae (NTHi) grown in medium containing no antibiotics or 0.25 MIC of amoxycillin, ciprofloxacin or loracarbef were examined for their effect on the ciliary beat frequency (CBF) and structure of human respiratory epithelium. CBF slowing was significantly (P < 0.05) less with 0.25 MIC of all three antibiotics. The epithelium was significantly (P < 0.05) less disrupted with ciprofloxacin. The morphology of NTHi infecting human adenoid organ cultures after 24 h with or without 0.25 MIC of the same antibiotics was measured by scanning electron microscopy. Only ciprofloxacin caused a significant (P < 0.05) change in morphology.
Article Reference Turnover of nonencapsulated Haemophilus influenzae in the nasopharynges of otitis-prone children.
Restriction enzyme analysis of total genomic DNA was applied to study the epidemiology of nontypeable Haemophilus influenzae (NTHI) isolated from the nasopharynges of children with recurrent acute otitis media (AOM). The turnover of strains, as judged from genetic fingerprinting of a total of 213 H. influenzae isolates collected prospectively during a 2-year study period from 38 children under 3 years of age, was examined in relation to episodes of AOM as well as to courses of antibiotic treatment. The children were selected if they had had at least one episode of AOM before 1 year of age and if more than two nasopharyngeal isolates of H. influenzae were recovered. The 213 H. influenzae isolates (90% NTHI) recovered corresponded to 128 different DNA fingerprints. Fifty-eight percent of the fingerprints were observed only once, whereas 42% appeared on two or more occasions in isolates from the same individual or in close relatives, i.e., brothers and sisters. Sixty-seven percent of these strains had a minimum colonization period of 2 months or less. Intermittent nasopharyngeal colonization periods longer than 5 months could be demonstrated for 13% of the strains. The present data suggest that intermittent colonization is due to endogenous reinfections. Genetically identical NTHI strains from unrelated individuals were never identified. As expected from the observation of a relatively high proportion of persistent colonizations, no correlation was found between episodes of AOM and the acquisition of new strains of H. influenzae, nor was any direct relation between antimicrobial therapy and the elimination of nasopharyngeal colonization with a particular strain of H. influenzae observed.