Effect of pathological changes of pH, pO2 and pCO2 on the activity of antimicrobial agents in vitro

Improved characterization of aminoglycoside penetration into human lung epithelial lining fluid via population pharmacokinetics

Aminoglycosides are important treatment options for serious lung infections, but modeling analyses to quantify their human lung epithelial lining fluid (ELF) penetration are lacking. We estimated the extent and rate of penetration for five aminoglycosides via population pharmacokinetics from eight published studies. The area under the curve in ELF vs plasma ranged from 50% to 100% and equilibration half-lives from 0.61 to 5.80 h, indicating extensive system hysteresis. Aminoglycoside ELF peak concentrations were blunted, but overall exposures were moderately high.

Antibacterial and anti-biofilm activities of walnut pellicle extract (Juglans regia L.) against coagulase-negative staphylococci

Juglans regia L. (common walnut) is a deciduous tree belonging to Juglandaceae family. Since ancient time, walnut was widely used in traditional medicine for its antioxidant, antidiabetic, antimicrobial, anti-inflammatory, anti-atherogenic and liver-protective effects. In this work, the antibacterial and anti-biofilm activities of walnuts pellicle extract against coagulase-negative staphylococci were evaluated. Qualitative chemical analysis was performed by the thin layer chromatography. UPLC-Ms/Ms was used to identify the chemical composition of J. regia extract. The total flavonoid and phenolic contents were determined by the Aluminium chloride and Folin-Ciocalteu methods, respectively. The extract showed antibacterial activity with MIC ranging from 3.60 to 461.75 µg/ml and MBC ranging from 461.75 to >461.75 µg/ml. Furthermore, it significantly reduced biofilm biomass and cell viability in a dose-dependent manner. Biological activities of J. regia extract may be due to its high flavonoid and phenolic contents. The obtained results are promising and they deserve further scientific investigations.

Compatibility of ciprofloxacin with commercial peritoneal dialysis solutions

Intraperitoneal administration of antibiotics together with peritoneal dialysis fluids (PDFs) remains the preferable route for treatment of peritoneal dialysis-related peritonitis. For home based therapy, antibiotic-containing PDFs are stored for up to two weeks and warmed up to body-temperature before administration. The present study investigated the compatibility of ciprofloxacin with five commercial PDFs at refrigeration-temperature, room-temperature and body-temperature. Ciprofloxacin concentrations were determined using high-performance liquid chromatography. Drug-diluent stability was evaluated by measurement of pH-values and visual inspection at each sampling point. The antimicrobial activity of ciprofloxacin was assessed by an E. coli disk diffusion method. Ciprofloxacin was stable at refrigeration-temperature and body-temperature in all PDFs evaluated over the whole study period of 14 days and 24 hours, respectively. At room-temperature, in contrast, ciprofloxacin demonstrated only limited stability in particular when tested in mixed Physioneal. Except for Physioneal 1.36%, no relevant drug adsorption was observed and the antimicrobial activity of ciprofloxacin was found to be preserved in each PDF at each storage condition investigated. Intraperitoneal ciprofloxacin might be used for inpatient and home based therapy of peritoneal dialysis-related peritonitis and no compensatory dose adjustment is needed when stored for up to two weeks at refrigeration-temperature before use.

Evaluation of local instillation of antibiotics in infected walled-off pancreatic necrosis

BACKGROUND

Infected walled-off pancreatic necrosis (WON) is associated with increased morbidity and mortality. Systemic antibiotics are the main treatment, but are associated with adverse reactions and risk of superinfections. This study evaluates the efficacy of local instillation of antibiotics into WON.

METHODS

We performed a retrospective cohort study of all consecutive patients with infected WON, who were treated with endoscopic transmural drainage and necrosectomy (ETDN) at a tertiary referral hospital between 2012 and 2016. A total of 91 patients were included. Patients often received concomitant intravenous and local antibiotics. Local antibiotics were added to the irrigation fluid depending on microbiological findings. A beneficial response was defined as the eradication of a microbe on subsequent culturing. Univariable and multivariable logistic regression analyses were used to evaluate antimicrobial efficacy.

RESULTS

At the first drainage 81 (86%) patients had infected and 10 sterile WON. Among patients with bacterial infections, neither local nor systemic antibiotics were associated with the eradication of microbes between first and second culture. Between the second and third culture, the use of local antibiotics was associated with the eradication of microbes (OR, 2.54; 95% CI, 1.25-5.18; p = 0.01), but not systemic antibiotics (OR, 0.75; 95% CI, 0.38-1.38; p = 0.33). Twelve patients had fungal infections treated with local amphotericin B between first and second culture. The fungus was eradicated in all 12 patients.

CONCLUSION

Local instillation of antibiotics may be a promising supplement to systemic administration.

Analysis of MIC and Disk Diffusion Testing Variables for Gepotidacin and Comparator Agents against Select Bacterial Pathogens

This study was conducted to determine the effect of testing parameters on the in vitro activity of gepotidacin, a new triazaacenaphthylene antibacterial agent for the treatment of conventional and biothreat pathogens. CLSI methods, and variations of those methods, were used to test 10 Staphylococcus aureus, 10 Streptococcus pneumoniae, 10 Haemophilus influenzae, and 5 Escherichia coli isolates by MIC and 30 S. aureus, 15 S. pneumoniae, and 15 S. pyogenes isolates by disk diffusion (DD) methods. Levofloxacin and linezolid were tested as comparator agents for MIC and DD methods, respectively. Broth microdilution (BMD), macrodilution (MD), and agar dilution (AD) methods were compared. Variations in media, temperature, incubation time, CO₂ level, and inoculum concentration were tested by all methods, and variations in pH, calcium, magnesium, zinc, potassium, thymidine, and polysorbate 80 levels were tested by BMD and DD. The addition of albumin, serum, and lung surfactant was studied by BMD. The variables that impacted the results the most were high inoculum and pH 5.5 (no growth of H. influenzae and S. pneumoniae by BMD). Gepotidacin AD MIC levels were increased and disk zone diameters were decreased for all species in 10% CO₂ incubation. The following variables had a minimal effect on gepotidacin results: pH, agar method, atmospheric condition, temperature, and addition of serum and albumin for broth methods. There were also some slight differences in gepotidacin disk results between disk manufacturers and some agar types and also with potassium and thymidine for S. pneumoniae For all other variations, gepotidacin MIC and disk results were considered comparable to reference results.

Amikacin Optimal Exposure Targets in the Hollow-Fiber System Model of Tuberculosis

Aminoglycosides such as amikacin are currently used for the treatment of multidrug-resistant tuberculosis (MDR-TB). However, formal pharmacokinetic/pharmacodynamic (PK/PD) studies to identify amikacin exposures and dosing schedules that optimize Mycobacterium tuberculosis killing have not been performed. It is believed that aminoglycosides do not work well under acidic conditions, which, if true, would mean poor sterilizing activity against semidormant bacilli at low pH. We performed time-kill studies to compare the bactericidal effect of amikacin in log-phase-growth bacilli with the sterilizing effect in semidormant bacilli at pH 5.8 in broth. In log-phase M. tuberculosis at normal pH versus semidormant M. tuberculosis at pH 5.8, the maximal kill (Emax) estimate and 95% confidence interval (CI) were 5.39 (95% CI, 4.91 to 5.63) versus 4.88 (CI, 4.46 to 5.22) log10 CFU/ml, while the concentration mediating 50% of Emax (EC50) was 1.0 (CI, 0. 0.86 to 1.12) versus 0.60 (CI, 0.50 to 0.66) times the MIC, respectively. Thus, the optimal exposures and kill rates identified for log-phase M. tuberculosis will be optimal even for semidormant bacilli. Next, we performed exposure-response and dose-scheduling studies in the hollow-fiber system model of tuberculosis using log-phase M. tuberculosis We recapitulated the amikacin concentration-time profiles observed in lungs of patients treated over 28 days. The PK/PD index linked to M. tuberculosis kill was the peak concentration (Cmax)-to-MIC ratio (r(2) > 0.99), closely followed by the area under the concentration-time curve from 0 to 24 h (AUC0-24)-to-MIC ratio (r(2) = 0.98). The EC90 was a Cmax/MIC ratio of 10.13 (95% CI, 7.73 to 12.48). The EC90 is the dosing target for intermittent therapy that optimizes cure in TB programs for MDR-TB patients.

Pharmacokinetic and pharmacodynamic implications in inhalable antimicrobial therapy

Inhaled antimicrobials provide a promising alternative to the systemically delivered drugs for the treatment of acute and chronic lung infections. The delivery of antimicrobials via inhalation route decreases the systemic exposure while increasing the local concentration in the lungs, enabling the use of antimicrobials with severe systemic side effects. The inhalation route of administration has several challenges in pharmacokinetic (PK) and pharmacodynamic (PD) assessments. This review discusses various issues that need to be considered during study, data analysis, and interpretation of PK and PD of inhaled antimicrobials. Advancements overcoming the challenges are also discussed.

N-acetylcysteine selectively antagonizes the activity of imipenem in Pseudomonas aeruginosa by an OprD-mediated mechanism

The modulating effect of N-acetylcysteine (NAC) on the activity of different antibiotics has been studied in Pseudomonas aeruginosa. Our results demonstrate that, in contrast to previous reports, only the activity of imipenem is clearly affected by NAC. MIC and checkerboard determinations indicate that the NAC-based modulation of imipenem activity is dependent mainly on OprD. SDS-PAGE of outer membrane proteins (OMPs) after NAC treatments demonstrates that NAC does not modify the expression of OprD, suggesting that NAC competitively inhibits the uptake of imipenem through OprD. Similar effects on imipenem activity were obtained with P. aeruginosa clinical isolates. Our results indicate that imipenem-susceptible P. aeruginosa strains become resistant upon simultaneous treatment with NAC and imipenem. Moreover, the generality of the observed effects of NAC on antibiotic activity was assessed with two additional bacterial species, Escherichia coli and Acinetobacter baumannii. Caution should be taken during treatments, as the activity of imipenem may be modified by physiologically attainable concentrations of NAC, particularly during intravenous and nebulized regimes.

pH modulates the activity and synergism of the airway surface liquid antimicrobials β-defensin-3 and LL-37

The pulmonary airways are continuously exposed to bacteria. As a first line of defense against infection, the airway surface liquid (ASL) contains a complex mixture of antimicrobial factors that kill inhaled and aspirated bacteria. The composition of ASL is critical for antimicrobial effectiveness. For example, in cystic fibrosis an abnormally acidic ASL inhibits antimicrobial activity. Here, we tested the effect of pH on the activity of an ASL defensin, human β-defensin-3 (hBD-3), and the cathelicidin-related peptide, LL-37. We found that reducing pH from 8.0 to 6.8 reduced the ability of both peptides to kill Staphylococcus aureus. An acidic pH also attenuated LL-37 killing of Pseudomonas aeruginosa. In addition, we discovered synergism between hBD-3 and LL-37 in killing S. aureus. LL-37 and lysozyme were also synergistic. Importantly, an acidic pH reduced the synergistic effects of combinations of ASL antibacterials. These results indicate that an acidic pH reduces the activity of individual ASL antimicrobials, impairs synergism between them, and thus may disrupt an important airway host defense mechanism.

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.

'To bead or not to bead?' Treatment of osteomyelitis and prosthetic joint-associated infections with gentamicin bead chains

Gentamicin-containing polymethylmethacrylate (PMMA) beads are frequently used to prevent and treat orthopaedic infections. The beads are typically inserted to fill anatomical defects secondary to surgical debridement. Local gentamicin use results in low serum levels whilst achieving high concentrations at the site of infection. However, a systematic review of the available literature showed that, despite these theoretical advantages, no prospective study has thus far proven gentamicin-containing PMMA beads to be effective in treating orthopaedic infections. Available studies are based on small patient numbers and do not show significantly better results when local and parenteral antibiotics are combined compared with systemic therapy alone. These poor results may be explained partially by reduced aminoglycoside efficacy when biofilms or gentamicin-resistant bacteria are present. Moreover, little is known regarding the potential side effects of gentamicin-containing beads. In this paper, the pros and cons regarding the use of gentamicin-containing PMMA beads are discussed. It is concluded that more well-executed, prospective studies are needed to settle the discussion on the use of gentamicin-containing beads in the treatment of orthopaedic infections.

Hospital-acquired pneumonia in the 21st century: a review of existing treatment options and their impact on patient care

Hospital-acquired pneumonia is a common nosocomial infection, with significant morbidity and mortality, and represents a major therapeutic challenge to clinicians. The therapeutic approach must be patient-oriented and institution-specific. The specific risk factors of each patient, such as previous antibiotic exposure, underlying diseases, length of hospital stay and the local patterns of antimicrobial resistance, should guide physicians in their decision of the initial optimal empirical therapy. Delays in the initiation or inappropriate/inadequate initial therapy are related to increased mortality and worse outcomes. In responding patients, as soon as culture data are available, efforts should be made to change the initial broad spectrum antibiotic regimen to a more targeted one (de-escalation). The optimal duration of treatment is a matter of debate, but courses longer than 1 week are rarely justified.

Influence of inoculum size of Staphylococcus aureus and Pseudomonas aeruginosa on in vitro activities and in vivo efficacy of fluoroquinolones and carbapenems

OBJECTIVES

We investigated the effect of inoculum size on MIC, bactericidal activity and the post-antibiotic effect (PAE) of carbapenems (imipenem, panipenem and meropenem) and injectable quinolones (pazufloxacin and ciprofloxacin) against Staphylococcus aureus and Pseudomonas aeruginosa, and also the relationship between in vivo systemic infection by changing the inoculum size injected in mice.

RESULTS

Increasing the bacterial inoculum (10(5)-10(8) cfu/mL) had no significant effect on the MIC of any of the tested antimicrobial agents. With the standard inocula (10(6) cfu/mL) of both test strains, all the antimicrobial agents showed bactericidal activity; however, increasing the inoculum size to >10(8) cfu/mL resulted in a reduction in bactericidal activity of all the antimicrobial agents against S. aureus Smith. In contrast, increasing the inoculum size of P. aeruginosa exerted only a minimal influence on the bactericidal activity of fluoroquinolones, but resulted in a reduction in the bactericidal activity of carbapenems. With the standard inoculum size of S. aureus Smith, pre-incubation with fluoroquinolones and carbapenems, except for meropenem, was sufficient to produce PAEs. When the inoculum was increased, the duration of the PAEs of these antimicrobial agents was reduced; however, those of fluoroquinolones were longer than carbapenems. Inoculum size had a greater influence on the in vivo efficacy of carbapenems than that of fluoroquinolones.

CONCLUSIONS

Our results suggest that decreased bactericidal activity, or the in vitro PAE of carbapenems and fluoroquinolones, is related to the reduced in vivo protective effect against infection caused by high inoculum with S. aureus or P. aeruginosa.

Design, synthesis and biological evaluation of oxazolidinone-quinolone hybrids

Oxazolidinone-quinolone hybrids that combine the pharmacophores of a quinolone and an oxazolidinone were synthesised and shown to be active against a variety of resistant and susceptible Gram-positive and fastidious Gram-negative organisms. The best compounds in this series overcome all types of resistance in relevant clinical Gram-positive pathogens. The nature of the spacer greatly influences the antibacterial activity. The dual mode of action could be demonstrated for compounds having a piperazinyl spacer. Antibacterial activity was higher at acidic pH.

Interactions among strategies associated with bacterial infection: pathogenicity, epidemicity, and antibiotic resistance

Infections have been the major cause of disease throughout the history of human populations. With the introduction of antibiotics, it was thought that this problem should disappear. However, bacteria have been able to evolve to become antibiotic resistant. Nowadays, a proficient pathogen must be virulent, epidemic, and resistant to antibiotics. Analysis of the interplay among these features of bacterial populations is needed to predict the future of infectious diseases. In this regard, we have reviewed the genetic linkage of antibiotic resistance and bacterial virulence in the same genetic determinants as well as the cross talk between antibiotic resistance and virulence regulatory circuits with the aim of understanding the effect of acquisition of resistance on bacterial virulence. We also discuss the possibility that antibiotic resistance and bacterial virulence might prevail as linked phenotypes in the future. The novel situation brought about by the worldwide use of antibiotics is undoubtedly changing bacterial populations. These changes might alter the properties of not only bacterial pathogens, but also the normal host microbiota. The evolutionary consequences of the release of antibiotics into the environment are largely unknown, but most probably restoration of the microbiota from the preantibiotic era is beyond our current abilities.

In vitro bactericidal activity of piperacillin, gentamicin, and metronidazole in a mixed model containing Escherichia coli, Enterococcus faecalis, and Bacteroides fragilis

An anaerobic, mixed model assay was used to study the bactericidal activities of piperacillin, gentamicin, and metronidazole, alone and in double- and triple-antibiotic combinations against a polymicrobial suspension of E. coli, E. faecalis, and B. fragilis. Only slight differences were noted with the agents when tested against single (10(5) cfu/mL inoculum) versus polymicrobic suspensions (10(6) cfu/mL final inoculum) of susceptible and resistant organisms. Contrary to previous reports in the literature, metronidazole was not active against E. coli in an anaerobic environment (even in the presence of B. fragilis) nor was the activity of metronidazole reduced against B. fragilis in the presence of E. faecalis. Gentamicin demonstrated excellent activity against E. coli when tested in a Bactron anaerobic chamber (5% hydrogen, 5% CO(2,) 90% nitrogen). The pH of the media was only reduced to 6.3-6.7, considerably higher than the pH range of 5-6 needed to significantly reduce the activity of aminoglycosides.

Identification of bacteria from a non-healing diabetic foot wound by 16 S rDNA sequencing

Approximately 10-20% of diabetic foot wounds fail initial antibiotic treatment. It is generally believed that several bacterial species may be present in these types of wounds. Because some of these organisms cannot be easily cultured, proper identification is problematic and thus, appropriate treatment modalities cannot be applied. This report examined the bacterial flora present in a chronic diabetic foot wound that failed antibiotic treatment. A tissue sample was collected from the base of the wound and used for standard microbiological culturing. DNA from the sample was used to amplify bacterial 16 S rDNA gene sequences and a library of these sequences was made. The clones were placed into two major groups on the basis of their melting temperatures. Representatives of these groups were sequenced, and information was used to identify the bacteria present in the wound. The culture-based method identified a single anaerobic species, Bacteroides fragilis. The method employing rDNA sequencing identified B. fragilis as a dominant organism and Pseudomonas (Janthinobacterium) mephitica as a minor component. The results indicate that rDNA sequencing approach can be an important tool in the identification of bacteria from wounds.

Effect of pH on in vitro antimicrobial susceptibility of the Bacteroides fragilis group

We studied the effect of pH (7.1, 6.3, and 5.8) on the in vitro susceptibilities of 59 isolates of Bacteroides fragilis and 60 isolates of other B. fragilis group species to trovafloxacin, ciprofloxacin, clindamycin, ampicillin-sulbactam, piperacillin-tazobactam, imipenem, and meropenem. For each agent tested the geometric mean MIC was highest at pH 5.8, intermediate at pH 6.3, and lowest at pH 7.1. The magnitude of the pH effect varied greatly among different antibiotics. These data show that an acidic pH decreases the in vitro susceptibilities of the B. fragilis group to several antibiotics.

Monitoring pH of otitis media effusion in chinchillas using fluorescence spectroscopy

We have developed a fiber optic fluorometer to measure fluorescent signal intensities across an epithelium barrier. As a medically relevant example, we have measured the pH of the effusion formed during Hemophilus influenzae induced otitis media infection in the chinchilla, the classical animal model for human middle ear disease. Because the choice of antibiotic used in clinical therapy is dependent on the pH of the effusion, a noninvasive method of measuring pH is highly desirable. Using the fluorescent pH probe carboxy-seminapthorhodafluor, we were able to detect pH changes of 0.15 units in the pH range around 7.0. The development and resolution of the otitis media was followed with magnetic resonance imaging to confirm the presence of the effusion formed during the infection.

Roles of divalent cations and pH in mechanism of action of nitroxoline against Escherichia coli strains

The antibacterial activity of nitroxoline (NIT), an antibiotic used in the treatment of acute or recurrent urinary tract infections caused by Escherichia coli, is decreased in the presence of Mg2+ and Mn2+ but not Ca2+. In order to elucidate the interaction between this drug and the divalent cations, spectrophotometric studies based on the natural absorption of the nitroxoline moiety were conducted. In the presence of the divalent metal ions, a shift in the NIT A448 suggested the formation of drug-ion complexes, for which the stability followed the order Mn2+ > Mg2+ > Ca2+. A clear correlation was found between the chelating property and antibacterial activity of NIT; both were pH dependent. A convenient colorimetric method for the determination of NIT uptake by bacterial cells was also developed. Uptake was energy independent and showed biphasic kinetics: a rapid association with cells and then a slower increase in cell-associated NIT which reached a plateau. NIT uptake was reduced in the presence of magnesium. The implications of metal ion complexation and pH on the clinical efficacy of NIT are discussed.