In vitro activities of metronidazole and its hydroxy metabolite against Bacteroides spp

Antimicrobial Transformation Products in the Aquatic Environment: Global Occurrence, Ecotoxicological Risks, and Potential of Antibiotic Resistance

The global spread of antimicrobial resistance (AMR) is concerning for the health of humans, animals, and the environment in a One Health perspective. Assessments of AMR and associated environmental hazards mostly focus on antimicrobial parent compounds, while largely overlooking their transformation products (TPs). This review lists antimicrobial TPs identified in surface water environments and examines their potential for AMR promotion, ecological risk, as well as human health and environmental hazards using in silico models. Our review also summarizes the key transformation compartments of TPs, related pathways for TPs reaching surface waters and methodologies for studying the fate of TPs. The 56 antimicrobial TPs covered by the review were prioritized via scoring and ranking of various risk and hazard parameters. Most data on occurrences to date have been reported in Europe, while little is known about antibiotic TPs in Africa, Central and South America, Asia, and Oceania. Occurrence data on antiviral TPs and other antibacterial TPs are even scarcer. We propose evaluation of structural similarity between parent compounds and TPs for TP risk assessment. We predicted a risk of AMR for 13 TPs, especially TPs of tetracyclines and macrolides. We estimated the ecotoxicological effect concentrations of TPs from the experimental effect data of the parent chemical for bacteria, algae and water fleas, scaled by potency differences predicted by quantitative structure-activity relationships (QSARs) for baseline toxicity and a scaling factor for structural similarity. Inclusion of TPs in mixtures with their parent increased the ecological risk quotient over the threshold of one for 7 of the 24 antimicrobials included in this analysis, while only one parent had a risk quotient above one. Thirteen TPs, from which 6 were macrolide TPs, posed a risk to at least one of the three tested species. There were 12/21 TPs identified that are likely to exhibit a similar or higher level of mutagenicity/carcinogenicity, respectively, than their parent compound, with tetracycline TPs often showing increased mutagenicity. Most TPs with increased carcinogenicity belonged to sulfonamides. Most of the TPs were predicted to be mobile but not bioaccumulative, and 14 were predicted to be persistent. The six highest-priority TPs originated from the tetracycline antibiotic family and antivirals. This review, and in particular our ranking of antimicrobial TPs of concern, can support authorities in planning related intervention strategies and source mitigation of antimicrobials toward a sustainable future.

Comparative pharmacokinetics of metronidazole in healthy and Trichomonas gallinae infected pigeons (Columba livia, var. domestica)

1. This study investigated the pharmacokinetics of metronidazole after intravenous (i.v.) and oral administration to healthy and experimentally Trichomonas gallinae-infected pigeons, and determined the in vitro antiprotozoal activity of metronidazole against T. gallinae.2. Twelve pigeons which were experimentally infected to T. gallinae and twelve healthy pigeons received metronidazole at the dose of 25 mg/kg by oral or i.v. administration. Serial blood sampling was used for pharmacokinetic analysis. The metronidazole minimum lethal concentration (MLC) and the concentration killing 50% of the trophozoites (LC₅₀) in the culture media were determined.3. In vitro data showed that the 24 h LC₅₀ and MLC of metronidazole were 0.31 and 25 µg/ml, respectively. In vivo results showed no statistical differences between pharmacokinetics in infected and non-infected pigeons for both routes of administration. The area under the curve was statistically higher after the i.v. administration in both infected and healthy pigeons. The mean oral bioavailability was similar in the infected (83.8%) and the healthy (81.5%) birds.4. In conclusion, the pharmacokinetics of metronidazole in pigeons was not affected by experimentally-induced trichomoniasis. Despite in vitro susceptibility testing, which showed probable resistance of the isolated T. gallinae to metronidazole, five-day oral treatment of infected pigeons with 25 mg/kg metronidazole twice a day resulted in total eradication of trophozoites recovered in crop lavage of infected birds.

A Putative Amidase Endolysin Encoded by Clostridium perfringens St13 Exhibits Specific Lytic Activity and Synergizes with the Muramidase Endolysin Psm

Clostridium perfringens is an often-harmful intestinal bacterium that causes various diseases ranging from food poisoning to life-threatening fulminant disease. Potential treatments include phage-derived endolysins, a promising family of alternative antimicrobial agents. We surveyed the genome of the C. perfringens st13 strain and identified an endolysin gene, psa, in the phage remnant region. Psa has an N-terminal catalytic domain that is homologous to the amidase_2 domain, and a C-terminal domain of unknown function. psa and gene derivatives encoding various Psa subdomains were cloned and expressed in Escherichia coli as N-terminal histidine-tagged proteins. Purified His-tagged full-length Psa protein (Psa-his) showed C. perfringens-specific lytic activity in turbidity reduction assays. In addition, we demonstrated that the uncharacterized C-terminal domain has cell wall-binding activity. Furthermore, cell wall-binding measurements showed that Psa binding was highly specific to C. perfringens. These results indicated that Psa is an amidase endolysin that specifically lyses C. perfringens; the enzyme’s specificity is highly dependent on the binding of the C-terminal domain. Moreover, Psa was shown to have a synergistic effect with another C. perfringens-specific endolysin, Psm, which is a muramidase that cleaves peptidoglycan at a site distinct from that targeted by Psa. The combination of Psa and Psm may be effective in the treatment and prevention of C. perfringens infections.

Poly(alizarin red S) modified glassy carbon electrode for square wave adsorptive stripping voltammetric determination of metronidazole in tablet formulation

Potentiodynamically fabricated poly(alizarin red s) modified GCE was characterized using CV and EIS techniques. In contrast to the cyclic voltammetric response of the unmodified GCE for metronidazole, an irreversible reduction peak with three-folds of current enhancement and reduced overpotential at the poly(alizarin red s) modified GCE showed the catalytic effect of the modifier towards reduction of metronidazole. While observed peak potential shift with increasing pH (4.0-10.0) indicated the involvement of protons during the reduction of metronidazole, peak potential shift with scan rate (20-300 mV s-1) confirmed the irreversibility of the reduction reaction of metronidazole at the modified GCE. A better correlation for the dependence of peak current on scan rate (r2 = 0.9883) than on square root of scan rate (r2 = 0.9740) supplemented by slope value of 0.38 for plot of log(current) versus log(scan rate) indicated the reduction reaction of metronidazole at the surface of the modified electrode was predominantly adsorption controlled. Under the optimized method and solution parameters, reductive current response of tablet sample showed linear dependence on spiked standard concentration in a wide range (0-125 μM) with excellent determination coefficient r2, LoD and LoQ of 0.9991, 0.38, and 1.25 μM, respectively. Spike recovery of 97.9% and interference recovery of 96.2-97.5% in the presence of 21.28 and 31.92 μM of uric acid and ascorbic acid validated the applicability of the present method for determination of metronidazole in tablet formulation. The metronidazole content of the tested tablet formulation using standard addition method was found to be 97.6% of what is claimed by the tablet manufacturer making the developed method an excellent potential candidate for its applicability to determine metronidazole in real samples with complex matrix.

Metronidazole removal by means of a combined system coupling an electro-Fenton process and a conventional biological treatment: By-products monitoring and performance enhancement

In order to mineralize Metronidazole (MTZ), a process coupling an electro-Fenton pretreatment and a biological degradation was implemented. A mono-compartment batch reactor containing a carbon-felt cathode and a platinum anode was employed to carry out the electro-Fenton pretreatment of MTZ. A total degradation of MTZ (100 mg L^-1) was observed at 0.07 mA.cm^-2 after only 20 min of electrolysis. Yet, after 1 and 2 h of electrolysis, the mineralization level remained low (16.2% and 32% respectively), guaranteeing a significant residual organic content for further biological treatment. LCMS/MS was used to determine the intermediates by-products and hence to propose a plausible degradation pathway. An increase from 0 to 0.44 and 0.6 for 1 and 2 h of electrolysis was observed for the BOD₅/COD ratio. Thus, from 1 h of electro-Fenton pretreatment, the electrolysis by-products were considered biodegradable. A biological treatment of the electrolysis by-products after 1 and 2 h was then realized. The mineralization yields reached very close values, about 84% for 1 and 2 h of electrolysis after 504 h of biological treatment, namely close to 89% for the overall process, showing the pertinence of the proposed coupled process.

Application of solid phase microextraction followed by liquid chromatography-mass spectrometry in the determination of antibiotic drugs and their metabolites in human whole blood and tissue samples

A sensitive, rapid and specific analytical method using high performance liquid chromatography coupled with mass spectrometry (HPLC-QqQ-MS) was developed to determine selected antibiotic drugs and their metabolites (amoxicillin, cefotaxime, ciprofloxacin, clindamycin and metronidazole; amoxycilloic acid, 4-hydroxyphenyl glycyl amoxicillin, desacetyl cefotaxime, 3-desacetyl cefotaxime lactone, ciprofloxacin N-oxide, N-demethylclindamycin, clindamycin sulfoxide, and hydroxy metronidazole) in human whole blood and vascularized tissue after single oral administration. The samples were prepared by solid phase microextraction with C18 fibers (SPME_C18) and determined on a GRACE analytical C18 column, Vision HT (50 × 2 mm, 1.5 μm) at the flow rate of 0.4 mL min^-1 using water and acetonitrile (containing 0.1% formic acid) as the mobile phase. The proposed method was successfully applied in a pharmacokinetic study of the selected antibiotic drugs and their metabolites in real human samples. Additionally, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI/TOF-MS) was used for identification and qualification analysis of the target compounds.

Electrochemistry-mass spectrometry for in-vitro determination of selected chemotherapeutics and their electrochemical products in comparison to in-vivo approach

Chemotherapeutics are among the most frequently prescribed medications in modern medicine. They are widely prescribed; however, problems with organisms developing resistance to these drugs means that their efficacy may be lost, so care should be taken to avoid unnecessary prescription. It is therefore of great interest to study the detailed metabolism of these biologically active compounds. This study aimed at developing an efficient analytical protocol for the determination of in-vitro electrochemical products of selected antibiotic drugs (amoxicillin, cefotaxime, fluconazole, linezolid, metronidazole and moxifloxacin). Combination of electrochemistry (EC) and mass spectrometry (MS) was applied for the in-vitro determination of the studied antibiotics and their electrochemical products. To identify the structure of the detected electrochemical products, MS/MS experiments were performed. This was one of the first applications of the EC system for generation of electrochemical products produced from antibiotic drugs. Adjustment of appropriate conditions and such parameters as the potential value, mobile phase (pH), working electrode and temperature had significant influence on electrochemical simulations and the creation of selected derivatives. Consequently, several working electrodes were evaluated for this purpose. In most of the studied cases, mainly two types of products were observed. One corresponded to an increase in mass by 14Da, which can be explained by a process consisting of oxidation (+16 m/z) and dehydrogenation (-2 m/z); The second in turn showed mass reduction by 14Da, which can be attributed to the loss of -CH2 as a result of N-demethylation. The performed experiments consisted of two stages: electrochemical oxidation of the analyzed samples (phase I of metabolic transformation), and addition of glutathione (GSH) for follow-up reactions (phase II conjunction). The electrochemical results were compared to in-vivo experiments by analyzing urine samples from patients after antibiotic drugs have been administered.. Overall, the comparison of electrochemistry to in-vivo experiments shows the high potential of EC-MS as a fast analytical tool in the prediction of electrochemical conversion that could be applied to therapeutic drug monitoring and pharmacokinetic studies as well.

Electrochemical Determination of Metronidazole in Tablet Samples Using Carbon Paste Electrode

Cyclic voltammetric investigation of metronidazole at carbon paste electrode revealed an irreversible reduction peak centered at about -0.4 V. Observed peak potential shift with pH in the range 2.0 to 8.5 indicated the involvement of protons during the reduction of metronidazole, whereas the peak potential shift with scan rate in the range 10-250 mV/s confirmed the irreversibility of the reduction reaction. A better correlation coefficient for the dependence of peak current on the scan rate than on the square root of scan rate indicated an adsorption controlled kinetics. Under the optimized method and solution parameters, an excellent linearity between the reductive peak current and the concentration of metronidazole was observed in the concentration range 1.0 × 10(-6) to 5.0 × 10(-4) M with a correlation coefficient, method detection limit (based on s = 3σ), and limit of quantification of 0.999, 2.97 × 10(-7) M and 9.91 × 10(-7) M, respectively. Good recovery results for spiked metronidazole in tablet samples and selective determination of metronidazole in tablet formulations in the presence of selected potential interferents such as rabeprazole, omeprazole, and tinidazole confirmed the potential applicability of the developed method for the determination of metronidazole in real samples like pharmaceutical tablets.

Benzodiazepine in a urine specimen without drug metabolites

CLINICAL HISTORY

PATIENT

41-year-old Hispanic woman. Chief Complaint: Pain in the neck, joints, and shoulders that started in August 2013. History of Present Illness: The patient has a history of psychiatric illness. Her primary care physician from an outside facility had prescribed alprazolam (Xanax) to treat her depression. The patient reported that in 2011 she experienced pain in the right side of her back and was diagnosed with sciatica. In addition, she was diagnosed with systemic lupus erythematosus (SLE) based on a positive finding for antinuclear antibodies (ANA) and double-stranded DNA (ds-DNA). She had not consulted a rheumatologist before this visit, nor had she received any medication for these conditions. Her recent history of symptoms included photosensitivity, painful aphthous ulcers, transient rashes, joint pain, myalgias, and bruising. The results of the most recent evaluation of her SLE serology revealed negative ANA and ds-DNA results. The current medications that the patient has been prescribed at Santa Clara Valley Medical Center include lamotrigine (Lamictal), sertraline (Zoloft), and gabapentin (Neurontin). In April 2014, the patient requested additional pain medication, such as hydrocodone/acetaminophen (Norco), during her physician visit. Consequently, as part of her pain management therapy agreement to ensure compliance,(1) she was subjected to a urine toxicology drug screening. At this time, her urine specimen, from an unwitnessed collection, tested positive for benzodiazepines using the Syva EMIT immunoassay (Siemens AG, Munich, Germany) at the cutoff of 200 ng/mL. However, results of a confirmatory test conducted via gas chromatography-mass spectrometry (GC/MS) did not identify any benzodiazepine metabolites in her urine but instead revealed the presence of a parent drug, alprazolam. Further, the same specimen tested positive for metronidazole. A visual inspection of the specimen revealed crystals on the bottom of the cup. In December 2013, this patient had tested positive for α-hydroxyalprazolam (an alprazolam metabolite; limit of detection, 10 ng/mL) and methamphetamine. At that time, she explained her positive urine-drug-test result by stating that "somebody had put something in my drink." Family history: Her father has been diagnosed with gout, knee osteoarthritis, and enlarged heart. Her brother has been diagnosed with clinical depression. Social history: Divorced; 3 children in the custody of their father; reported having smoked 0.5 packs of cigarettes per day for 20 years; denied any alcohol intake or illicit drug use.

Pharmacologically active drug metabolites: impact on drug discovery and pharmacotherapy

Metabolism represents the most prevalent mechanism for drug clearance. Many drugs are converted to metabolites that can retain the intrinsic affinity of the parent drug for the pharmacological target. Drug metabolism redox reactions such as heteroatom dealkylations, hydroxylations, heteroatom oxygenations, reductions, and dehydrogenations can yield active metabolites, and in rare cases even conjugation reactions can yield an active metabolite. To understand the contribution of an active metabolite to efficacy relative to the contribution of the parent drug, the target affinity, functional activity, plasma protein binding, membrane permeability, and pharmacokinetics of the active metabolite and parent drug must be known. Underlying pharmacokinetic principles and clearance concepts are used to describe the dispositional behavior of metabolites in vivo. A method to rapidly identify active metabolites in drug research is described. Finally, over 100 examples of drugs with active metabolites are discussed with regard to the importance of the metabolite(s) in efficacy and safety.

Effects of antibiotics on bacterial species composition and metabolic activities in chemostats containing defined populations of human gut microorganisms

The composition and metabolic activities of the human colonic microbiota are modulated by a number of external factors, including diet and antibiotic therapy. Changes in the structure and metabolism of the gut microbiota may have long-term consequences for host health. The large intestine harbors a complex microbial ecosystem comprising several hundreds of different bacterial species, which complicates investigations on intestinal physiology and ecology. To facilitate such studies, a highly simplified microbiota consisting of 14 anaerobic and facultatively anaerobic organisms (Bacteroides thetaiotaomicron, Bacteroides vulgatus, Bifidobacterium longum, Bifidobacterium infantis, Bifidobacterium pseudolongum, Bifidobacterium adolescentis, Clostridium butyricum, C. perfringens, C. bifermentans, C. innocuum, Escherichia coli, Enterococcus faecalis, Enterococcus faecium, Lactobacillus acidophilus) was used in this investigation. Ampicillin [9.2 μg (ml culture)(-1)] was added to two chemostats operated at different dilution rates (D; 0.10 h(-1) and 0.21 h(-1)), and metronidazole [76.9 μg (ml culture)(-1)] was added to a third vessel (D = 0.21 h(-1)). Perturbations in bacterial physiology and metabolism were sampled over a 48-h period. Lactobacillus acidophilus and C. bifermentans populations did not establish in the fermentors under the imposed growth conditions. Ampicillin resulted in substantial reductions in bacteroides and C. perfringens populations at both dilution rates. Metronidazole strongly affected bacteroides communities but had no effect on bifidobacterial communities. The bacteriostatic effect of ampicillin on bifidobacterial species was growth rate dependent. Several metabolic activities were affected by antibiotic addition, including fermentation product formation and enzyme synthesis. The growth of antibiotic-resistant bifidobacteria in the large bowel may enable them to occupy ecological niches left vacant after antibiotic administration, preventing colonization by pathogenic species.

Low-level resistance of Staphylococcus aureus to thrombin-induced platelet microbicidal protein 1 in vitro associated with qacA gene carriage is independent of multidrug efflux pump activity

Thrombin-induced platelet microbial protein 1 (tPMP-1), a cationic antimicrobial polypeptide released from thrombin-stimulated rabbit platelets, targets the Staphylococcus aureus cytoplasmic membrane to initiate its microbicidal effects. In vitro resistance to tPMP-1 correlates with survival advantages in vivo. In S. aureus, the plasmid-carried qacA gene encodes a multidrug transporter, conferring resistance to organic cations (e.g., ethidium [Et]) via proton motive force (PMF)-energized export. We previously showed that qacA also confers a tPMP-1-resistant (tPMP-1r) phenotype in vitro. The current study evaluated whether (i) transporters encoded by the qacB and qacC multidrug resistance genes also confer tPMP-1r and (ii) tPMP-1r mediated by qacA is dependent on efflux pump activity. In contrast to tPMP-1r qacA-bearing strains, the parental strain and its isogenic qacB- and qacC-containing strains were tPMP-1 susceptible (tPMP-1s). Efflux pump inhibition by cyanide m-chlorophenylhydrazone abrogated Etr, but not tPMP-1r, in the qacA-bearing strain. In synergy assays, exposure of the qacA-bearing strain to tPMP-1 did not affect the susceptibility of Et (ruling out Et-tPMP-1 cotransport). The following cytoplasmic membrane parameters did not differ significantly between the qacA-bearing and parental strains: contents of the major phospholipids; asymmetric distributions of the positively charged species, lysyl-phosphotidylglycerol; fatty acid composition; and relative surface charge. Of note, the qacA-bearing strain exhibited greater membrane fluidity than that of the parental, qacB-, or qacC-bearing strain. In conclusion, among these families of efflux pumps, only the multidrug transporter encoded by qacA conferred a tPMP-1r phenotype. These data suggest that qacA-encoded tPMP-1r results from the impact of a specific transporter upon membrane structure or function unrelated to PMF-dependent peptide efflux.

Solid phase synthesis of a metronidazole oligonucleotide conjugate

Direct, solid phase synthesis of an oligonucleotide conjugate of the antibiotic drug metronidazole was accomplished by the phosphoramidite method. Removal of protecting groups and cleavage from the controlled pore glass (CPG) solid support was successful using mild conditions (20% Et(3)N in pyridine, then conc. NH(3) (aq) at rt for 30 min) whereas standard conditions (conc. NH(3) (aq) at 55 degrees C for 16 h) cleaved the drug.

Pharmacokinetics and pharmacodynamics of intravenous levofloxacin at 750 milligrams and various doses of metronidazole in healthy adult subjects

The purpose of this investigation was to evaluate the steady-state pharmacokinetics, pharmacodynamics, and safety of intravenous levofloxacin at 750 mg administered once daily combined with three different dosages of intravenous metronidazole (500 mg every 8 h [q8h], 1,000 mg q24h, and 1,500 mg q24h). Eighteen healthy adult subjects received all three combinations in a randomized, crossover fashion. Serial blood and urine samples were collected on the third day of each study period. The 24-h areas under the inhibitory (AUIC(0-24)) and bactericidal (AUBC(0-24)) curves of these three combination regimens were determined against clinical isolates of Bacteroides fragilis, Bacteroides thetaiotaomicron, Peptostreptococcus asaccharolyticus, and Escherichia coli. The mean concentrations of levofloxacin were not different between study periods and were similar to those previously published. The mean (+/- standard deviation) areas under the metronidazole plasma concentration-time curve (AUC(0-24)) for 1,500-mg q24h (338 +/- 105 mg.h/liter) and 500-mg q8h (356 +/- 68 mg.h/liter) regimens were not different (P > 0.05), but both were significantly higher than the 1,000-mg q24h AUC(0-24) (P < 0.05, 227 +/- 57 mg.h/liter). Mean (+/- standard deviation) total body clearance and renal clearance values were similar among the 500-mg q8h, 1,000-mg q24, and 1,500-mg q24h regimens (62 +/- 7, 67 +/- 13, and 67 +/- 14 and 11 +/- 3, 12 +/- 2, and 12 +/- 5 ml/min/1.73 m2, respectively). Levofloxacin at 750 mg q24h plus metronidazole at 500 mg q8h or 1,500 mg q24h resulted in similar AUIC(0-24) and AUBC(0-24) values with one exception: the AUIC(0-24) for the 1,500-mg q24h regimen against B. thetaiotamicron was significantly higher (P < 0.05) than those of the other regimens. Overall, the combination of levofloxacin at 750 mg once daily and metronidazole at 500 mg q8h or 1,500 mg q24h appeared to have greater AUIC(0-24) and AUBC(0-24) values than did the 1,000-mg q24h regimen. All combination regimens of levofloxacin and metronidazole were well tolerated, and no serious drug-related adverse effects were reported. The pharmacokinetic, safety, and pharmacodynamic data from our study suggest that a once-daily regimen of intravenous levofloxacin at 750 mg and metronidazole at 1,500 mg warrants further clinical investigation.

Application of cutaneous microdialysis to evaluate metronidazole and its main metabolite concentrations in the skin after a single oral dose

OBJECTIVE

To measure the concentration of metronidazole and its hydroxymetabolite in plasma and cutaneous microdialysates and to compare metronidazole penetration into cutaneous microdialysates against theoretical predicted penetration in a peripheral compartment.

METHOD

A single oral dose of 2 g of the parent drug was administered to 10 healthy male volunteers. Microdialysis probes with 2 kDa molecular weight cut-off were inserted intradermally and were perfused with Ringer solution up to 8 h after drug ingestion. Drug and metabolite concentrations were measured by high performance liquid chromatography.

RESULTS

Mean maximum concentration in plasma, cutaneous microdialysates and theoretical peripheral compartment were 214 +/- 49, 151 +/- 52 and 146 +/- 38 micromol/L, respectively, and were achieved after about 2.1 +/- 0.8, 2.8 +/- 1.0 and 6.0 +/- 2.9 h. The extent of penetration into cutaneous microdialysates and theoretical peripheral compartment relative to plasma were 0.672 +/- 0.196 and 0.675 +/-0.207, respectively, and did not differ significantly. Moreover, maximum concentration as well as area under concentration-time curve in these compartments also did not differ significantly.

CONCLUSION

Use of cutaneous microdialysis technique permits the characterization of true systemic drug disposition, for optimizing drug treatment strategies.

Efficacy of antigiardial drugs

The flagellated protozoa Giardia duodenalis is the most commonly detected parasite in the intestinal tract of humans. Infections with the parasite result in diarrhoeal disease in humans and animals, with infants at risk from failure-to-thrive syndrome. The incidence of giardiasis worldwide may be as high as 1000 million cases. Current recommended treatments include the nitroheterocyclic drugs tinidazole, metronidazole and furazolidone, the substituted acridine, quinacrine, and the benzimidazole, albendazole. Paromomycin is also used in some situations, and nitazoxanide is proving to be useful. However, treatment failures have been reported with all of the common antigiardial agents, and drug resistance to all available drugs has been demonstrated in the laboratory. In addition, clinical resistance has been reported, including cases where patients failed both metronidazole and albendazole treatments. The identification of new antigiardial drugs is an important consideration for the future, but maintaining the usefulness of the existing drugs is the most cost-effective measure to ensure the continued availability of antigiardial drugs.

Role of antimicrobial susceptibility testing on efficacy of triple therapy in Helicobacter pylori eradication

BACKGROUND

Helicobacter pylori treatment failure may be due to resistance to macrolides and 5-nitroimidazoles.

AIM

To test whether a preliminary in vitro susceptibility test of H. pylori to tinidazole and clarithromycin and a consequent specific regimen could improve the eradication rate.

METHODS

A total of 109 consecutive H. pylori-positive patients with dyspeptic symptoms were included. At endoscopy, biopsy from the antrum was obtained for H. pylori culture and antimicrobial susceptibility testing. Fifty-six patients were treated with omeprazole, tinidazole and clarithromycin for 10 days (group OTC) and 53 patients received therapy on the basis of the susceptibility test (group SUSC). Treatment success was evaluated by the 13C-urea breath test 1 month after the end of therapy.

RESULTS

Eight patients dropped out. Overall primary resistance to clarithromycin, tinidazole and both antibiotics was 13%, 33% and 4%, respectively. In group OTC, H. pylori was eradicated in 81% and 75% of patients by per protocol and intention-to-treat analysis, respectively. Per protocol and intention-to-treat eradication rates for group SUSC were 98% and 91% (P < 0.05 vs. group OTC).

CONCLUSIONS

These data show that in H. pylori infection, antibiotic therapy based on the results of culture and susceptibility testing gives, in comparison to standard therapy, a significant improvement in eradication rate.

QacA multidrug efflux pump from Staphylococcus aureus: comparative analysis of resistance to diamidines, biguanidines, and guanylhydrazones

The staphylococcal multidrug efflux pump QacA mediates resistance to a broad spectrum of monovalent and divalent antimicrobial cations. Resistance toward various classes of these compounds identified features of the substrate that may be important for interaction with QacA. Analysis of combinations of two substrates suggested that the same mechanism is used for the extrusion of different classes of compounds.

The toxic effect of the antibiotic metronidazole on aquatic organisms

The acute toxicity of metronidazole was tested on freshwater and marine organisms. The tests showed effect on Chlorella sp. and Selenastrum capricornutum. 72-hr EC10 of 2.03 mg/l and 19.9 mg/l respectively and 72-hr EC50 values of 12.5 mg/l and 40.4 mg/l respectively were among the results obtained. No acute lethal effect was observed on Acartia tonsa or Brachydanio rerio. The study demonstrates the potential ecotoxic effect of metronidazole, suggesting the need for further investigations of the environmental exposure of medicinal substances.

In vitro activity of clarithromycin alone and in combination with ciprofloxacin or levofloxacin against Legionella spp.: enhanced effect by the addition of the metabolite 14-hydroxy clarithromycin

Clarithromycin is metabolized to an active metabolite, 14-hydroxy clarithromycin. These compounds have demonstrated excellent in vitro activity against Legionella species, with both agents having significantly lower MICs than erythromycin. Using a checkerboard assay, the activity of clarithromycin and its hydroxy metabolite, alone and in combination, was examined against 41 Legionella organisms. The activity of clarithromycin and 14-hydroxy clarithromycin, in a 2:1 ratio, plus ciprofloxacin or levofloxacin was also determined. Activity of the antibiotic combinations was determined by calculating the fractional inhibitory concentration index. An agar dilution method using buffered charcoal yeast extract media was used for susceptibility and synergy testing. An inoculum of 10(4) CFU/spot was used, with all plates incubated at 35 degrees C for 48 h. The MIC90 for clarithromycin or 14-hydroxy clarithromycin alone was 0.5, versus 0.25 microgram/mL for the combination. Additive effects were observed with clarithromycin and its hydroxy metabolite for 61% of the Legionella species, with fractional inhibitory concentration indices ranging from 0.63 to 1.25. The 14-hydroxy metabolite significantly increased the activity of both fluoroquinolone/clarithromycin combinations. Based on these data, in vitro susceptibility testing of agents such as clarithromycin should be reevaluated to account for the activity of active metabolites.