Levofloxacin plus metronidazole administered once daily versus moxifloxacin monotherapy against a mixed infection of Escherichia coli and Bacteroides fragilis in an in vitro pharmacodynamic model

Antibiotic Resistance and Mechanisms of Pathogenic Bacteria in Tubo-Ovarian Abscess

A tubo-ovarian abscess (TOA) is a common type of inflammatory lump in clinical practice. TOA is an important, life-threatening disease, and it has become more common in recent years, posing a major health risk to women. Broad-spectrum antimicrobial agents are necessary to cover the most likely pathogens because the pathogens that cause TOA are polymicrobial. However, the response rate of antibiotic treatment is about 70%, whereas one-third of patients have poor clinical consequences and they require drainage or surgery. Rising antimicrobial resistance serves as a significant reason for the unsatisfactory medical outcomes. It is important to study the antibiotic resistance mechanism of TOA pathogens in solving the problems of multi-drug resistant strains. This paper focuses on the most common pathogenic bacteria isolated from TOA specimens and discusses the emerging trends and epidemiology of resistant Escherichia coli, Bacteroides fragilis, and gram-positive anaerobic cocci. Besides that, new methods that aim to solve the antibiotic resistance of related pathogens are discussed, such as CRISPR, nanoparticles, bacteriophages, antimicrobial peptides, and pathogen-specific monoclonal antibodies. Through this review, we hope to reveal the current situation of antibiotic resistance of common TOA pathogens, relevant mechanisms, and possible antibacterial strategies, providing references for the clinical treatment of drug-resistant pathogens.

Mechanisms of Bacteroides fragilis resistance to metronidazole

Metronidazole-resistant Bacteroides fragilis (B. fragilis) have been reported worldwide. Several mechanisms contribute to B. fragilis resistance to metronidazole. In some cases, the mechanisms of metronidazole resistance are unknown. Understanding the mechanisms of resistance is important for therapy, the design of new alternative drugs, and control of resistant strains. In this study, a comprehensive review of the B. fragilis resistance mechanisms to metronidazole was prepared. The rate of metronidazole-resistant B. fragilis has been reported as ranging from 0.5% to 7.8% in many surveys. According to CLSI, isolates with MICs ≥32 μg/mL are considered to be metronidazole-resistant. In the majority of cases, metronidazole resistance in B. fragilis is coupled with the existence of nim genes. Metronidazole resistance could be induced in nim-negative strains by exposure to sub-MIC levels of metronidazole. There are multi-drug efflux pumps in B. fragilis which can pump out a variety of substrates such as metronidazole. The recA overexpression and deficiency of feoAB are other reported metronidazole resistance mechanisms in this bacterium.

In Vitro Anaerobic Pharmacokinetic/Pharmacodynamic Model to Simulate the Bactericidal Activity of Levornidazole Against Bacteroides fragilis

PURPOSE

This study was designed to correlate the pharmacokinetic/pharmacodynamic (PK/PD) parameters with PD indices of levornidazole against Bacteroides fragilis and to calculate the PK/PD target value for levornidazole to attain its expected maximal bactericidal effect using an in vitro anaerobic dynamic PK/PD model.

METHODS

An anaerobic dynamic PK/PD model was developed in vitro. The scheme for PK modeling was designed according to the PK parameters of levornidazole in the human body. The device of 2-compartment PK/PD model was constructed by using digital control of flow rate to simulate 4 regimens of single-dose intravenous infusion of levornidazole to determine the bactericidal activity of levornidazole against the 3 strains of B fragilis within 72 hours. PD parameters such as reduction of colony count within 24 hours (∆Log_24h), area under bactericidal curve (AUBC), and 2-hour initial killing rate (IKR) were calculated and correlated with PK/PD parameters. Sigmoid E_max model of levornidazole was established to calculate PK/PD target values to attain corresponding PD effect.

FINDINGS

PK and PD validation proved the stability of the model in simulating levornidazole against B fragilis and the precision and accuracy in the results of PK modeling. C_max and AUC_0-24h found only -1.46% and -6.72% differences from the values in vivo. Our study found that ∆Log_24h, AUBC, and IKR were more correlated with AUC_0-24h/MIC and C_max/MIC than with %T>MIC. According to ∆Log_24h, the PK/PD target values of AUC_0-24h/MIC, C_max/MIC, and %T>MIC of levornidazole against B fragilis were 157.6%, 14.1%, and 56.4%, respectively.

IMPLICATIONS

Our findings are useful for optimizing the clinical dosing regimen of levornidazole sodium chloride injection to attain maximal bactericidal effect.

Effect of pore size and morphology of activated charcoal prepared from midribs of Elaeis guineensis on adsorption of poisons using metronidazole and Escherichia coli O157:H7 as a case study

Agricultural waste obtained from Elaeis guineensis mid ribs can provide a veritable source of materials which can be used as precursor materials for the production of pharmaceutical grade activated charcoal. The pore size and surface morphology of activated charcoal defines the types of molecules that could be adsorbed unto it, as surface morphology plays a significant role in determining the surface availability and areas of adsorption.

The activated charcoal samples prepared from Elaeis guineensis via either physical or chemical activation was characterized via surface area using the BET method and subsequently pore structure and size analyzed by scanning electron microscopy (SEM).

Physically activated Elaeis guineensis fronds activated with nitrogen gas had wide spread microporosity with micropore volume of 0.232 cc/g compared to the chemically activated with 1M and 3M phosphoric acid respectively. The commercial activated charcoal/metronidazole combination in the in vitro-pharmacodynamic model reflected no re-growth after 4 hours, however for charcoal formulated from Elaeis guineensis via chemical activation with 3M phosphoric acid and metronidazole no regrowth was seen at the second hour and this was maintained throughout the duration of the experiment.

Increased macroporosity enhanced bacterial adsorption and this was further facilitated by the presence of antibacterial metronidazole in the in vitro pharmacodynamic model. Activated charcoal produced from agricultural waste obtained from Elaeis guineensis dried mid ribs consisting of increased macroporosity with mixed meso/micro porosity and antibacterial metronidazole form the best model for bacterial adsorption and will be useful in the treatment of diarrhea caused by E. coli O157:H7.

Metronidazole Single versus Multiple Daily Dosing in Serious Intraabdominal/Pelvic and Diabetic Foot Infections

The purpose of the study was to compare the clinical efficacy of once-daily versus multiple dose regimens of metronidazole in inpatients with serious/systemic Bacteroides fragilis infections, i.e., intraabdominal/pelvic and diabetic foot infections. A retrospective chart review was performed on 145 adult inpatients who received combination therapy with metronidazole for B. fragilis abdominal/pelvic infection or diabetic (deep) foot infections/osteomyelitis. Exclusion criteria included metronidazole given for indications other than those mentioned, patients who received only one dose of metronidazole, and patients who received oral metronidazole only. The 145 patients were in two groups: 66 patients in the metronidazole 1 g (i.v.) q24h (Group A) and 79 patients who received metronidazole 500 mg (i.v./p.o.) q6-8h dosing (Group B). Patient demographics included age, gender, indications of metronidazole, concomitant, antibiotics, and co-morbidities. Data collection also included length of stay (LOS), antibiotic days, and clinical outcomes. The 145 patients in our study had a mean age of 66 years, 61% were female and 39% male. Most patients were being treated for definitive intraabdominal/pelvic infections (82%), or probable intraabdominal/pelvic infections (22%). Only 6% had deep diabetic foot infections of osteomyelitis (percentages exceed 100% since a patient can have more than one indication) and were included since B. fragilis is also and important pathogen in diabetic osteomyelitis. Group A patients had more concomitant antibiotics and co-morbidities (p < 0.0001 and p < 0.05 respectively, chi-square test for trend) than Group B patients. There were no statistically significant differences between groups A and B for LOS and antibiotic days (p = 0.42 and p = 0.92 respectively, by rank-sum test), but after adjusting for concomitant antibiotics and co-morbidities Group A patients had clinically shorter LOS and fewer antibiotic days. Unadjusted mortality and failure rates were non-significantly higher in group A (relative ratios of 12.1%/6.3% = 6.3% = 1.91 and 18.2%/ 10.1% = 1.80 respectively), but after adjusting for concomitant antibiotics and co-morbidities with stratification analysis, groups A and B were virtually the same (risk differences of </= 1%). The authors conclude that for B. fragilis infections, as part of combination therapy, metronidazole 1 g (i.v.) q 24h appears to eb as efficacious and not inferior to multiply-dosed metronidazole regimens. Once daily metronidazole, i.e., 1 g (i.v.) q24h for the treatment of serious systemic infections where B. fragilis is an important co-pathogen (intraabdominal/pelvic and deep diabetic foot infections) has pharmacokinetic and pharmaco-economic advantages.

Moxifloxacin in the treatment of skin and skin structure infections

Moxifloxacin is a recent addition to the fluoroquinolone class, differing from ciprofloxacin and other older agents in having much better in vitro activity against Gram-positive aerobes while retaining potent activity against Gram-negative aerobes. It is also active against the pathogens of human and animal bite wounds and those species of atypical mycobacteria associated with dermatologic infections. Its activity against anaerobes is quite variable. Moxifloxacin penetrates well into inflammatory blister fluid and muscle and subcutaneous adipose tissues. Moxifloxacin should thus be a reasonable option for the treatment of skin and skin structure infections (SSSIs). In 3 randomized controlled trials (RCTs), oral moxifloxacin was as effective as cephalexin in the treatment of uncomplicated SSSIs in adults while in 2 RCTs, intravenous/oral moxifloxacin was as effective as intravenous/oral β-lactam/β-lactamase inhibitor therapy in the treatment of complicated SSSIs in adults. Moxifloxacin does not inhibit cytochrome P450 enzymes and thus interact with warfarin or methylxanthines. However, multivalent cations can reduce its oral bioavailability substantially. Dosage adjustment is not required in the presence of renal or hepatic impairment. The clinical relevance of its electrophysiologic effects (QT_c prolongation) remains unresolved.

In vitro activities of moxifloxacin and tigecycline against bacterial isolates associated with intraabdominal infections at a medical center in Taiwan, 2001-2006

A total of 569 nonduplicate isolates recovered from patients with community-onset or hospital-onset intraabdominal infections (IAIs) from 2001 to 2006 were studied. These included 28 Staphylococcus aureus and 541 Gram-negative isolates (33.6% Escherichia coli, 29.0% Klebsiella pneumoniae, 8.1% Acinetobacter baumannii, and 6.3% Pseudomonas aeruginosa). Minimum inhibitory concentrations (MICs) of the isolates to moxifloxacin, imipenem, and ciprofloxacin were determined using the agar dilution method and to tigecycline using the broth microdilution method. Extended-spectrum beta-lactamase (ESBL) producers were found in 15.5% (29 out of 182) of E. coli, 15.3% (24 out of 157) of K. pneumoniae, and 15.4% (2 out of 13) of K. oxytoca isolates. More than 85% of Enterobacteriaceae were susceptible to moxifloxacin, but this percentage was lower among E. coli (78%). The percentage of E. coli (K. pneumoniae) isolates that were not susceptible to moxifloxacin was 6% (0%) in 2001, 39% (17%) in 2003, and 21% (14%) in 2006. Tigecycline exhibited good in vitro activities against all S. aureus and >95% of all Enterobacteriaceae tested. Among the 24 isolates of ESBL-producing K. pneumoniae, 4 had tigecycline MICs > or = 2 microg/ml. Eighty percent of A. baumannii isolates exhibited tigecycline MICs of < or = 2 microg/ml. This study found that moxifloxacin and tigecycline exhibited good in vitro activity against bacterial isolates causing IAIs.

Pharmacodynamics of moxifloxacin against a high inoculum of Escherichia coli in an in vitro infection model

OBJECTIVES

Escherichia coli is the leading bacterial species implicated in intra-abdominal infections. In these infections a high bacterial burden with pre-existing resistant mutants are likely to be encountered and resistance could be amplified with suboptimal dosing. Our objective was to investigate the pharmacodynamics of moxifloxacin against a high inoculum of E. coli using an in vitro hollow fibre infection model (HFIM).

METHODS

Three wild-type strains of E. coli (ATCC 25922, MG1655 and EC28044) were studied by exposing approximately 2 x 10(8) cfu/mL (20 mL) to escalating dosing regimens of moxifloxacin (ranging from 30 to 400 mg, once daily). Serial samples were obtained from HFIM over 120 h to enumerate the total and resistant subpopulation. Quinolone resistance-determining regions of gyrA and parC of resistant isolates were sequenced to confirm the mechanism of resistance.

RESULTS

The pre-exposure MIC of the three wild-type strains was 0.0625 mg/L. Simulated moxifloxacin concentration profiles in HFIM were satisfactory (r(2) >or= 0.94). Placebo experiments revealed natural mutants, but no resistance amplification. Regrowth and resistance amplification was observed between 30 mg/day (AUC/MIC = 47) and 80 mg/day dose (AUC/MIC = 117). Sustained bacterial suppression was achieved at >or=120 mg/day dose (AUC/MIC = 180). Point mutations in gyrA (D87G or S83L) were detected in resistant isolates.

CONCLUSIONS

Our results suggest that suboptimal dosing may facilitate resistance amplification in a high inoculum of E. coli. The clinical dose of moxifloxacin (400 mg/day) was adequate to suppress resistance development in three wild-type strains. Clinical relevance of these findings warrants further in vivo investigation.

In vitro activity of piperacillin/tazobactam and ertapenem against Bacteroides fragilis and Escherichia coli in pure and mixed cultures

Ertapenem and piperacillin/tazobactam are β-lactam antibiotics with a broad spectrum of activity used for the treatment of mixed infections in which Bacteroides fragilis and Escherichia coli play an important aetiological role. In this study, the activities of piperacillin/tazobactam and ertapenem (MIC and time–kill kinetics) against these bacteria were compared. MICs were determined by the agar dilution method, and the time and slope of time–kill curves were analysed. In the in vitro pharmacodynamic assays, pure and mixed cultures of E. coli and B. fragilis were exposed to peak concentrations of ertapenem (8.0 μg ml−1) and piperacillin/tazobactam (64.0/8.0 μg ml−1) for 48 h. Treatment with ertapenem reduced the viability of E. coli and/or B. fragilis by 3 logs in all experiments, whereas piperacillin/tazobactam only affected the viability of B. fragilis. Both drugs exhibited their fastest rates of killing when bacteria were grown in mixed cultures. According to the results, ertapenem exhibited activity similar to that of piperacillin/tazobactam against B. fragilis alone or in mixed culture. However, ertapenem exhibited a markedly higher activity against E. coli alone or in combination with B. fragilis relative to piperacillin/tazobactam.

Stability of cefepime and metronidazole prepared for simplified administration as a single product

The stabilities of cefepime and metronidazole were determined after preparation of a single admixture product in view of its potential use as a simple and cost-effective therapeutic alternative for infections caused by many aerobic and anaerobic pathogens. The stability of cefepime 1000 or 2000 mg mixed with metronidazole 500 or 1500 mg was evaluated via high-performance liquid chromatography after storage for up to 336 h at 4 or 23 degrees C. Cefepime was stable in all 4 degrees C samples for up to 336 h, retaining > or =95% of initial concentrations. Samples of cefepime 1000 and 2000 mg mixed with metronidazole 500 mg were stable at 23 degrees C for up to 48 h, whereas those mixed with metronidazole 1500 mg and cefepime controls were stable at 23 degrees C for up to 72 h. Metronidazole was stable in all samples for up to 336 h, retaining > or =94% of initial concentrations. These data suggest that therapeutic use of cefepime and metronidazole as a single intravenous admixture product is feasible and practical.

Fluoroquinolones and Anaerobes

The usefulness of fluoroquinolones for the treatment of mixed aerobic and anaerobic infections has been investigated since these agents started being used in clinical practice. Newer compounds have increased in vitro activity against anaerobes, but clinically relevant susceptibility breakpoints for these bacteria have not been established. Pharmacodynamic analyses and corroboration by new data from clinical trials have enhanced our knowledge concerning the use of fluoroquinolones to treat selective anaerobic pathogens. These studies suggest that newer agents could be useful in the treatment of several types of mixed aerobic and anaerobic infections, including skin and soft-tissue, intra-abdominal, and respiratory infections. The major concerns with expanding the use of fluoroquinolones to treat anaerobic infections have been reports of increasing resistance in Bacteroides group isolates and the impact of these antibiotics on the incidence of Clostridium difficile-associated disease.

Influence of Human Ascitic Fluid on theIn VitroAntibacterial Activity of Moxifloxacin

We investigated the in vitro influence of HAF on the antibacterial activity of moxifloxacin against Escherichia coli ATCC 10798, Escherichia coli K-12, Proteus rettgeri (Sanelli), Staphylococcus aureus ATCC 25923, Staphylococcus aureus NCTC 1808 and Staphylococcus epidermidis ATCC 12228. Human ascitic fluid was obtained from 6 cirrhotic patients by paracentesis. The interaction effect was evaluated by the checkerboard technique. Our results indicate the ability of human ascitic fluid to reduce minimum inhibitory concentrations of moxifloxacin against Gram-negative bacteria, but not against Gram-positives.