Kinetics and Quantification of Antibacterial Effects of Beta-Lactams, Macrolides, and Quinolones against Gram-Positive and Gram-Negative RTI Pathogens

Quantitative Microbial Risk Assessment of Antibiotic-Resistant E. coli, Legionella pneumophila, and Mycobacteria in Nonpotable Wastewater Reuse Applications

Antibiotic-resistant bacteria (ARB) have become a major threat to public health and modern medicine. A simple death kinetics-based dose-response model (SD-DRM) was incorporated into a quantitative microbial risk assessment (QMRA) to assess the risks of exposure to reclaimed wastewater harboring antibiotic-resistant E. coli, Legionella pneumophila, and Mycobacterium avium for multiple exposure scenarios. The fractions of ARB and trace antibiotics present in the body were incorporated to demonstrate their impact on infection risks. Both ARB and antibiotic susceptible bacteria, ASB, are assumed to have the same dose-response in the absence of antibiotics but behave differently in the presence of residual antibiotics in the body. Annual risk of L. pneumophila infection exceeded the EPA 10-4 pppy (per person per year) benchmark at concentrations in reclaimed water greater than 103-104 CFU/L, depending on parameter variation. Enteropathogenic E. coli infection risks meet the EPA annual benchmark at concentrations around 105-106 total E. coli. The results illustrated that an increase in residual antibiotics from 0 to 40% of the minimum inhibitory concentration (MIC) reduced the risk by about 1 order of magnitude for E. coli but was more likely to result in an untreatable infection.

Assessment of antibiotic-resistant infection risks associated with reclaimed wastewater irrigation in intensive tomato cultivation

Agricultural irrigation using reclaimed urban wastewater (RWW) represents a sustainable practice to meet the ever-increasing water stress in modern societies. However, the occurrence of residual antibiotics and antibiotic resistant bacteria (ARB) in RWW is an important human health concern. This study applied for the first time a novel Simple-Death dose-response model to the field data of Escherichia coli and Pseudomonas spp. collected from three greenhouses for cultivation of tomatoes irrigated with RWW. The model estimates the risk of infection by enteropathogenic E. coli associated with consumption of tomatoes and the risk of eye-infection caused by Pseudomonas aeruginosa in cultivation soil through hand-to-eye contacts. The fraction of antibiotic resistant (AR)-E. coli measured in irrigation water and AR-Pseudomonas spp. in soil was incorporated in the model to estimate the survival of ARB and antibiotic susceptible bacteria in the presence of trace level of antibiotics in human body. The results showed that the risk of E. coli infection through consumption of tomatoes irrigated with RWW is within the WHO and USEPA recommended risk threshold (<10-4); Pseudomonas aeruginosa eye-infection risk is at or below the acceptable risk level. The presence of residual antibiotic in human body reduced the overall risk probabilities of infections but selectively enhanced the survival of ARB in comparison to their susceptible counterparts, which resulted in antibiotic untreatable infection. Therefore, the outcomes of this study call for a new risk threshold for antibiotic untreatable infections and highlight the key importance of adopting work safety measures for better human health protection.

In vitro antimicrobial efficacy of Cassia alata (Linn.) leaves, stem, and root extracts against cellulitis causative agent Staphylococcus aureus

BACKGROUND

Cellulitis is a common skin disease encountered in medical emergencies in hospitals. It can be treated using a combination of antibiotics therapy; however, the causative agent Staphylococcus aureus has been reported to develop resistance towards the currently used antibiotics. Therefore, the search for more alternative herbal origin antimicrobial agents is critical.

AIM

In this study, maceration and Soxhlet extraction of the whole plant of Cassia alata Linn. (leaves, roots, and stem) were performed using four solvents with different polarities, namely n-hexane, ethyl acetate, ethanol and distilled water. The crude extracts were screened using agar well diffusion, colorimetric broth microdilution, grid culture and bacterial growth curve analysis against Staphylococcus aureus. The phytochemicals in the crude extracts were identified using Gas Chromatography-Mass Spectrometry (GC-MS).

RESULTS

Agar-well diffusion analysis revealed that extraction using ethyl acetate showed the largest inhibition zone with an average diameter of 15.30 mm (root Soxhlet extract) followed by 14.70 mm (leaf Soxhlet extract) and 13.70 mm (root maceration extract). The lowest minimum inhibitory and minimum bactericidal concentration in root Soxhlet extract using ethyl acetate was 0.313 and 0.625 µg µL^-1, respectively. Our study proved that crude extract of the plant suppressed the growth of S. aureus as evidenced from a significant regression extension (p < 0.06, p = 0.00003) of lag phase for 6 h after the treatment with increased concentration. Based on the GC-MS analysis, 88 phytochemicals consist of fatty acids, esters, alkanes, phenols, fatty alcohols, sesquiterpenoids and macrocycle that possibly contributed to the antimicrobial properties were identified, 32 of which were previously characterized for their antimicrobial, antioxidant, and anti-inflammatory activities.

CONCLUSION

Ethyl acetate crude extract was better than the other investigated solvents. The root and stem of C. alata showed significant antimicrobial efficacy against S. aureus in this study. The remaining 56 out of 88 phytochemicals of the plant should be intensively studied for more medicinal uses.

Peri-Operative Prophylaxis in Patients of Neonatal and Pediatric Age Subjected to Cardiac and Thoracic Surgery: A RAND/UCLA Appropriateness Method Consensus Study

Surgical site infections (SSIs) represent a potential complication of surgical procedures, with a significant impact on mortality, morbidity, and healthcare costs. Patients undergoing cardiac surgery and thoracic surgery are often considered patients at high risk of developing SSIs. This consensus document aims to provide information on the management of peri-operative antibiotic prophylaxis for the pediatric and neonatal population undergoing cardiac and non-cardiac thoracic surgery. The following scenarios were considered: (1) cardiac surgery for the correction of congenital heart disease and/or valve surgery; (2) cardiac catheterization without the placement of prosthetic material; (3) cardiac catheterization with the placement of prosthetic material; (4) implantable cardiac defibrillator or epicardial pacemaker placement; (5) patients undergoing ExtraCorporal Membrane Oxygenation; (6) cardiac tumors and heart transplantation; (7) non-cardiac thoracic surgery with thoracotomy; (8) non-cardiac thoracic surgery using video-assisted thoracoscopy; (9) elective chest drain placement in the pediatric patient; (10) elective chest drain placement in the newborn; (11) thoracic drain placement in the trauma setting. This consensus provides clear and shared indications, representing the most complete and up-to-date collection of practice recommendations in pediatric cardiac and thoracic surgery, in order to guide physicians in the management of the patient, standardizing approaches and avoiding the abuse and misuse of antibiotics.

Botanicals and phytochemicals from the bark of Hypericum roeperianum (Hypericaceae) had strong antibacterial activity and showed synergistic effects with antibiotics against multidrug-resistant bacteria expressing active efflux pumps

ETHNOPHARMACOLOGICAL RELEVANCE

Infections due to multidrug-resistant (MDR) bacteria constitute a real problem in the public health worldwide. Hypericum roeperianum Schimp. ex A. Rich (Hypericaceae) is used traditionally for treatment of various ailments such as abdominal pains, constipation, diarrhea, indigestion, nausea, and bacterial diseases.

AIM OF THE STUDY

This study was aimed at investigating the antibacterial and antibiotic-modifying activity of the crude methanol extracts (HRB), ethyl-acetate soluble fraction (HRBa), residual material (HRBb), and 11 compounds from the bark of Hypericum roeperianum against multi-drug resistant (MDR) bacteria expressing active efflux pumps.

MATERIALS AND METHODS

The antibacterial activity, the efflux pump effect using the efflux pump inhibitor (EPI), phenylalanine-arginine-ß-naphthylamide (PAβN), as well as the antibiotic-modifying activity of samples were determined using the broth micro-dilution method. Spectrophotometric methods were used to evaluate the effects of HRB and 8,8-bis(dihydroconiferyl) diferulate (11) on bacterial growth, and bacterial membrane damage, whereas follow-up of the acidification of the bacterial culture was used to study their effects on bacteria proton-ATPase pumps.

RESULTS

The crude extract (HRB), HRBa, and HRBb had selective antibacterial activity with MICs ranging from 16 to 512 μg/mL. Phytochemical 11 displayed the best antibacterial activity (0.5 ≤ MIC ≤ 2 μg/mL). The activity of HRB and 11 in the presence of EPI significantly increased on the tested bacteria strains (up to 32-fold). The activity of cloxacillin (CLO), doxycycline (DOX), and tetracycline (TET), was considerably improved (up to 64-fold) towards the multidrug-resistant Enterobacter aerogenes EA-CM64 strain. The crude extract (HRB) and 11 induced the leakage of bacterial intracellular components and inhibited the proton-ATPase pumps.

CONCLUSIONS

The crude extract (HRB) and 8,8-bis(dihydroconiferyl)diferulate from the bark of Hypericum roeperianum are good antibacterial candidates that deserve further investigations to achieve antibacterial drugs to fight infections involving MDR bacteria.

Antibacterial Efficacy of Eravacycline In Vivo against Gram-Positive and Gram-Negative Organisms

Members of the tetracycline class are frequently classified as bacteriostatic. However, recent findings have demonstrated an improved antibacterial killing profile, often achieving ≥3 log10 bacterial count reduction, when such antibiotics have been given for periods longer than 24 h. We aimed to study this effect with eravacycline, a novel fluorocycline, given in an immunocompetent murine thigh infection model over 72 h against two methicillin-resistant Staphylococcus aureus (MRSA) isolates (eravacycline MICs = 0.03 and 0.25 μg/ml) and three Enterobacteriaceae isolates (eravacycline MICs = 0.125 to 0.25 μg/ml). A humanized eravacycline regimen, 2.5 mg/kg of body weight given intravenously (i.v.) every 12 h (q12h), demonstrated progressively enhanced activity over the 72-h study period. A cumulative dose response in which bacterial density was reduced by more than 3 log10 CFU at 72 h was noted over the study period in the two Gram-positive isolates, and eravacycline performed similarly to comparator antibiotics (tigecycline, linezolid, and vancomycin). A cumulative dose response with eravacycline and comparators (tigecycline and meropenem) over the study period was also observed in the Gram-negative isolates, although more variability in bacterial killing was observed for all antibacterial agents. Overall, a bacterial count reduction of ≥3 log was achieved in one of the three isolates with both eravacycline and tigecycline, while meropenem achieved a similar endpoint against two of the three isolates. Bactericidal activity is typically defined in vitro over 24 h; however, extended regimen studies in vivo may demonstrate an improved correlation with clinical outcomes by better identification of antimicrobial effects.

Impact of Intraoperative Continuous-Infusion Versus Intermittent Dosing of Cefazolin Therapy on the Incidence of Surgical Site Infections After Coronary Artery Bypass Grafting

STUDY OBJECTIVES

To determine whether intraoperative continuous-infusion (CI) cefazolin reduces the incidence of surgical site infections (SSIs) compared with intermittent (INT) cefazolin dosing in patients undergoing coronary artery bypass grafting (CABG) on cardiopulmonary bypass (CPB); safety end points and protocol adherence comparing the two dosing strategies were also explored.

DESIGN

Retrospective quasi-experimental (pre-post intervention) cohort study.

SETTING

Large academic medical center.

PATIENTS

A total of 516 adults who underwent CABG on CPB and received cefazolin intraoperatively between June 1, 2013, and December 31, 2014, were included. The INT cohort included 284 patients who underwent CABG from June 2013 to February 2014. The CI cohort included 232 patients who underwent CABG from April to December 2014, after an intraoperative CI cefazolin protocol for cardiac surgery patients undergoing CPB was adopted in March 2014.

MEASUREMENTS AND MAIN RESULTS

The primary end point was incidence of SSIs, and safety end points of renal dysfunction and seizures were evaluated. Multivariable logistic regression analysis was used to determine the impact on SSIs when controlling for other risk factors. A subgroup analysis for this study included 2 months within each time period to evaluate protocol adherence. The overall incidence of SSIs was decreased in patients receiving CI cefazolin, although this did not reach statistical significance (4.6% in the INT cohort vs 1.7% in the CI cohort, p=0.116). Superficial SSIs were significantly reduced in the CI cohort (2.8% in the INT cohort vs 0.4% in the CI cohort, p=0.039). In the regression analysis, CI cefazolin decreased the odds of SSI by 66%, although it did not reach statistical significance (p=0.077). Safety end points were not significantly different between groups. Overall protocol adherence did not differ significantly between the cohorts: 77% in the INT cohort and 67% in the CI cohort (p=0.212).

CONCLUSION

CI cefazolin significantly decreased the incidence of superficial SSIs compared with INT cefazolin in patients undergoing CABG on CPB, without increasing the risk for adverse effects. As this study was underpowered to detect a significant difference in overall SSIs, larger, randomized studies are required to validate the superiority of CI cefazolin.

Influence of pharmacokinetics/pharmacodynamics of antibacterials in their dosing regimen selection

The choice of antimicrobial dosing in clinical practice in the past was based upon a 'penicillin mentality', that is, on the assumption that the in vivo antimicrobial efficacy is dependent on the duration of drug levels above the minimum inhibitory concentration of target microorganisms. Really, a rational antimicrobial therapy is strongly related to a basic understanding of the influence the patient has on the antibiotic (pharmacokinetics [PKs]) and the patient's response to the specific drug effects (pharmacodynamics [PDs]). PK/PD parameters are essential in facilitating the translation of microbiological activity into clinical situations, ensuring a successful outcome. This review will analyze the typical patterns of antimicrobial activity and the corresponding PK/PD parameters, with a special focus on a PK/PD dosing approach with the most commonly utilized antimicrobial agent classes.

Evaluation of pharmacokinetic/pharmacodynamic relationships of PD-0162819, a biotin carboxylase inhibitor representing a new class of antibacterial compounds, using in vitro infection models

The present study investigated the pharmacokinetic/pharmacodynamic (PK/PD) relationships of a prototype biotin carboxylase (BC) inhibitor, PD-0162819, against Haemophilus influenzae 3113 in static concentration time-kill (SCTK) and one-compartment chemostat in vitro infection models. H. influenzae 3113 was exposed to PD-0162819 concentrations of 0.5 to 16× the MIC (MIC = 0.125 μg/ml) and area-under-the-curve (AUC)/MIC ratios of 1 to 1,100 in SCTK and chemostat experiments, respectively. Serial samples were collected over 24 h. For efficacy driver analysis, a sigmoid maximum-effect (E(max)) model was fitted to the relationship between bacterial density changes over 24 h and corresponding PK/PD indices. A semimechanistic PK/PD model describing the time course of bacterial growth and death was developed. The AUC/MIC ratio best explained efficacy (r(2) = 0.95) compared to the peak drug concentration (C(max))/MIC ratio (r(2) = 0.76) and time above the MIC (T>MIC) (r(2) = 0.88). Static effects and 99.9% killing were achieved at AUC/MIC values of 500 and 600, respectively. For time course analysis, the net bacterial growth rate constant, maximum bacterial density, and maximum kill rate constant were similar in SCTK and chemostat studies, but PD-0162819 was more potent in SCTK than in the chemostat (50% effective concentration [EC(50)] = 0.046 versus 0.34 μg/ml). In conclusion, basic PK/PD relationships for PD-0162819 were established using in vitro dynamic systems. Although the bacterial growth parameters and maximum drug effects were similar in SCTK and the chemostat system, PD-0162819 appeared to be more potent in SCTK, illustrating the importance of understanding the differences in preclinical models. Additional studies are needed to determine the in vivo relevance of these results.

Comparative in vitro activities of the novel antibacterial finafloxacin against selected Gram-positive and Gram-negative bacteria tested in Mueller-Hinton broth and synthetic urine

Kill kinetics and MICs of finafloxacin and ciprofloxacin against 34 strains with defined resistance mechanisms grown in cation-adjusted Mueller-Hinton broth (CAMHB) at pH values of 7.2 and 5.8 and in synthetic urine at pH 5.8 were determined. In general, finafloxacin gained activity at low pH values in CAMHB and remained almost unchanged in artificial urine. Ciprofloxacin MICs increased and bactericidal activity decreased strain dependently in acidic CAMHB and particularly in artificial urine.

Cefazolin bolus and continuous administration for elective cardiac surgery: improved pharmacokinetic and pharmacodynamic parameters

OBJECTIVE

Cefazolin (1-2 g bolus at induction possibly repeated after cardiopulmonary bypass) remains the standard for antibiotic prophylaxis in cardiac surgery. Data indicate, however, that it is underdosed with this dosing schedule. A prospective, randomized study comparing intermittent versus loading dose plus continuous infusion for the same total dose of cefazolin was performed to assess which modality is pharmacokinetically and pharmacodynamically advantageous.

METHODS

Patients received 2 g cefazolin as a starting dose and then were divided into an intermittent group (receiving another 1 g at 3, 9, and 15 hours after the first dose) and a continuous group (continuous infusion started after the first dose, providing 1 g every 6 hours for 18 hours). Cefazolin levels were measured in blood and atria.

RESULTS

Mean total and calculated free trough concentrations in blood varied greatly among patients in the intermittent group and were lower than those in the continuous group (P < .05 at 15, 18 and 24 hours). For 9 of 10 (90%) patients in the continuous infusion group, the targeted pharmacokinetic and pharmacodynamic goal (time above minimal inhibitory concentration >90%) was achieved, whereas the goal was met for only 3 of 10 (30%) in the intermittent group (P < .05). The mean atrial tissue concentration was also higher with continuous infusion (P < .05).

CONCLUSIONS

Administration of cefazolin as bolus plus continuous infusion has pharmacokinetic and pharmacodynamic advantages relative to intermittent administration. It provides more stable serum levels, lower interpatient variability, and higher myocardial tissue penetration.

Isolation and identification of the antibacterial active compound from petroleum ether extract of neem oil

From a petroleum ether extract of neem oil (Azadirachta indica A. Juss) the new tetrahydrofuranyl diester 1 was isolated as an anti-bacterial constituent. 1 showed significant activities against three standard bacterial strains, including Staphylococcus aureus ATCC 25923, Escherichia coli ATCC 25922 and Salmonella enteritidis CMCC (B) 50041.

Bactericidal activity of cefepime and ceftriaxone tested against Streptococcus pneumoniae

The bactericidal activities of cefepime and ceftriaxone were assessed by testing a contemporary collection of 50 Streptococcus pneumoniae strains. Minimum inhibitory and bactericidal concentrations (MIC and MBC, respectively) of cefepime and ceftriaxone were determined, and time-kill studies were performed on 14 selected strains (10 penicillin-resistant, 2-intermediate, and 2-susceptible). Cefepime and ceftriaxone showed essentially identical potency (MIC50, 1 microg/mL and MIC90, 2 microg/mL, for both compounds) and MBC values (MBC50, 1 microg/mL for both). MBC/MIC ratios were < or = 4 for cefepime and < or = 8 for ceftriaxone on 48 (96.0%) strains, and 2 strains (4.0%) displayed MBC/MIC ratios > or = 32 (tolerance) to the 2 cephalosporins. Time-kill curves corroborated the MBC/MIC studies. Cefepime and ceftriaxone bactericidal activity (> or = 3 log10 CFU/mL reduction in inoculum) was demonstrable after 24 h of exposure to 8x MIC for 13 (92.9%) of 14 strains, whereas 1 strain showed approximately 2 log10 CFU/mL reduction. In conclusion, our results indicate that cefepime and ceftriaxone exhibit comparable potency and bactericidal activities when tested against contemporary pneumococcal strains with varying penicillin susceptibility patterns. Both parenteral cephems offer alternative therapeutic choices for the treatment of invasive pneumococcal infections.

Redefining penems

The antimicrobial class of penems has the potential to address most of the relevant resistance issues associated with beta-lactam antibiotics because of their exceptionally broad spectrum of antibacterial activity and their intrinsic stability against hydrolytic attack by many beta-lactamases including ESBL and AmpC enzymes. The subclass of carbapenems covers the spectrum of hospital pathogens whereas the subclass of penems covers community pathogens. The only currently available penem, faropenem, has a low propensity for resistance development, beta-lactamase induction and selection of carbapenem-resistant Pseudomonas aeruginosa. This makes it attractive for the treatment of community-acquired infections and for step-down or sequential therapy following carbapenem treatment without jeopardizing the activity of carbapenems or the entire beta-lactam class in the hospital environment.